{ "cells": [ { "cell_type": "markdown", "metadata": {}, "source": [ "# Introducción a Python para ciencias e ingenierías (notebook 1)\n", "\n", "Docente: Ing. Martín Gaitán \n", "\n", "Twitter: `@tin_nqn_`\n", "\n", "**Links útiles**\n", "\n", "Descarga de la suite \"Anaconda\" (Python 3.4)\n", "\n", "### http://continuum.io/downloads \n", "\n", "Repositorio de \"notebooks\" (material de clase)\n", "\n", "### http://bit.ly/cursopy\n", "\n", "Python \"temporal\" online: \n", "\n", "### http://try.jupyter.org\n" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "## ¡Empecemos! \n", "\n", "Python es un lenguaje de programación:\n", "\n", "* Interpretado e Interactivo\n", "* Fácil de aprender, programar y **leer** (menos *bugs*)\n", "* De *muy alto nivel*\n", "* Multiparadigma\n", "* Orientado a objetos\n", "* Libre y con licencia permisiva\n", "* Eficiente\n", "* Versátil y potente! \n", "* Con gran documentación\n", "* Y una gran comunidad de usuarios" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Instalación\n", "\n", "* En Windows o mac: recomendación [Anaconda](http://continuum.io/downloads). **Instalá la versión basada en Python 3** que corresponda a tu Sistema Operativo\n", "\n", "* En linux directamente podes instalar todo lo necesario desde tus repositorios. Por ejemplo en Ubuntu: \n", "\n", "```\n", "`sudo apt-get install ipython3-notebook python3-matplotlib python3-numpy python3-scipy`\n", "---- \n", "\n", "### ¿Cómo se usa Python?\n", "\n", "#### Consolas interactivas\n", "\n", "Hay muchas maneras de usar el lenguaje Python. Dijimos que es un lenguaje **interpretado** e **interactivo**. Si ejecutamos la consola (En windows `cmd.exe`) y luego `python`, se abrirá la consola interactiva\n", "\n", "![](files/img/console.png)\n", "\n", "En la consola interactiva podemos escribir sentencias o pequeños bloques de código que son ejecutados inmediatamente. Pero *la consola interactiva* estándar es **limitada**. Mucho mejor es usar **IPython**. \n", "\n", "![](files/img/ipython.png)\n", "\n", "La consola IPython supera a la estándar en muchos sentidos. Podemos autocompletar (``), ver ayuda rápida de cualquier objeto (`?`) y muchas cosas más. \n" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ipython Notebook (Jupyter)\n", "\n", "Y otra forma muy útil es usar los *Notebooks*. Jupyter es un entorno web para computación interactiva. \n", "\n", "\n", "
Si bien nació como parte del proyecto IPython, el mismo entorno visual se puede conectar a *\"kernels\"* de distintos lenguajes. Se puede usar Jupyter con Python, Julia, R, Octave y decenas de lenguajes más.
\n", "\n", "\n", "\n", "Podemos crear y editar \"celdas\" de código Python que podés editar y volver a ejecutar, podés intercalar celdas de texto, fórmulas matemáticas, y hacer que gráficos se muestren inscrutados en la misma pantalla. Estos archivos se guardan con extensión *.ipynb*, que pueden exportarse a diversos formatos estátucos como html o como código python puro. (.py)\n", "\n", "Los notebooks son muy útiles para la **\"programación exploratoria\"**, muy frecuente en ciencia e ingeniería\n", "\n", "Todo el material de estos cursos estarán en formato notebook.\n", "\n", "Para ejecutar IPython Notebook, desde la consola tipear:\n", "\n", "```\n", "jupyter notebook\n", "```\n", "\n", "\n" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Programas \n", "\n", "También podemos usar Python para hacer programas o scripts. \n", "Esto es, escribir nuestro código en un archivo con extensión `.py` y ejecutarlo con el intérprete de python. \n", "Por ejemplo, el archivo hello.py (al que se le llama módulo) tiene este contenido:\n", "\n", "```python\n", " print(\"¡Hola curso!\")\n", "```\n", "\n", "Si ejecutamos python scripts/hello.py se ejecutará en el interprete Python y obtendremos el resultado" ] }, { "cell_type": "code", "execution_count": 1, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Hola curso\n" ] } ], "source": [ "print('Hola curso')" ] }, { "cell_type": "code", "execution_count": 2, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "¡Hola curso!\r\n" ] } ], "source": [ "!python3 scripts/hello.py" ] }, { "cell_type": "code", "execution_count": 3, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\r\n", "(gedit:12526): Gtk-WARNING **: GtkScrolledWindow 0x2520880 is mapped but visible child GtkScrollbar 0x252caf0 is not mapped\r\n", "\r\n", "(gedit:12526): Gtk-WARNING **: GtkScrolledWindow 0x2520880 is mapped but visible child GtkScrollbar 0x252ccf0 is not mapped\r\n", "\r\n", "(gedit:12526): Gtk-WARNING **: GtkScrolledWindow 0x2520880 is mapped but visible child GtkScrollbar 0x252caf0 is not mapped\r\n", "\r\n", "(gedit:12526): Gtk-WARNING **: GtkScrolledWindow 0x2520880 is mapped but visible child GtkScrollbar 0x252ccf0 is not mapped\r\n" ] } ], "source": [ "!gedit" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "
IPython agrega muchas funcionalidades complementarias que no son parte del lenguaje Python. Por ejemplo el signo `!` que precede la línea anterior indica que se ejecutará un programa/comando del sistema en vez de código python
" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "\n", "### ¿Qué editor usar?\n", "\n", "Python no exige un editor específico y hay muchos modos y maneras de programar. \n", "\n", "Un buen editor orientado a Python científico es **Spyder**, que es un entorno integrado (editor + ayuda + consola interactiva)\n", "\n", "![](files/img/spyder.png)\n", "\n", "También el entorno Jupyter trae un editor sencillo\n", "\n", "![](files/img/editor.png)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### ¿Python 2 o Python 3? \n", "\n", "Hay dos versiones **actuales** de Python. La rama 2.7 (actualmente la version 2.7.9) y la rama 3 (actualmente 3.4)\n", "Todas las bibliotecas científicas de Python funcionan con ambas versiones. Pero ¡Python 3 es aún más fácil y es el que permanecerá a futuro!\n" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "\n", "# ¡Queremos programar!\n", "\n", "\n", "### En el principio: Números\n", "\n", "Python es un lenguaje de muy alto nivel y por lo tanto trae muchos *tipos* de datos incluidos. \n" ] }, { "cell_type": "code", "execution_count": 4, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "-9.6" ] }, "execution_count": 4, "metadata": {}, "output_type": "execute_result" } ], "source": [ "1 + 1.4 - 12" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Ejecuten su consola y ¡a practicar!" ] }, { "cell_type": "code", "execution_count": 16, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "25279070162814602892416332909167230989159750079826794382624239047131088637588624086108407495497996962875" ] }, "execution_count": 16, "metadata": {}, "output_type": "execute_result" } ], "source": [ "29348575847598437598437598347598435**3" ] }, { "cell_type": "code", "execution_count": 8, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "2" ] }, "execution_count": 8, "metadata": {}, "output_type": "execute_result" } ], "source": [ "5 % 3" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Los tipos numéricos básicos son *int* (enteros sin limite), *float* (reales, ) y *complex* (complejos)" ] }, { "cell_type": "code", "execution_count": 6, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "(6.4+24j)" ] }, "execution_count": 6, "metadata": {}, "output_type": "execute_result" } ], "source": [ "(3.2 + 12j) * 2" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "0.1 + 0.3" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "3 // 2" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "3 % 2" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las operaciones aritméticas básicas son:\n", "\n", "* adición: `+`\n", "* sustracción: `-`\n", "* multiplicación: `*`\n", "* división: `/`\n", "* módulo (resto de división): `%` \n", "* potencia: `**`\n", "* división entera: `//`" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las operaciones se pueden agrupar con paréntesis y tienen precedencia estándar " ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "x = 1.32\n", "resultado = ((21.2 + 4.5)**0.2 / x) + 1j\n", "print(resultado)\n", "resultado + 2" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Outs vs prints\n", "\n", "* La función `print` *imprime* (muestra) el resultado por pantalla y pero **no devuelve un valor** (estrictamente devuelve `None`). Quiere decir que el valor mostrado no queda disponible para seguir operando.\n", "* Si la última sentencia de una celda tiene un resultado distinto a `None`, se guarda y se muestra en `Out[x]`\n", "* Los últimas ejecuciones se guardan en variables automáticas `_`, `__` (última y anteúltima) o en general `_x` o `Out[x]`" ] }, { "cell_type": "code", "execution_count": 15, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "1" ] }, "execution_count": 15, "metadata": {}, "output_type": "execute_result" } ], "source": [ "int(1.4)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "1 + 2J" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "Out[6] # que es Out (sin corchetes)? Pronto lo veremos" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Más funciones matemáticas\n", "\n", "Hay muchas más *funciones* matemáticas y algunas constantes extras definidas en el *módulo* `math`" ] }, { "cell_type": "code", "execution_count": 17, "metadata": { "collapsed": true }, "outputs": [], "source": [ "import math # se importa el modulo para poder usar sus funciones" ] }, { "cell_type": "code", "execution_count": 18, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "-2.4492935982947064e-16" ] }, "execution_count": 18, "metadata": {}, "output_type": "execute_result" } ], "source": [ "math.sin(2*math.pi)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "# round es una función built-in\n", "round(5.6)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "round(math.pi, 4)" ] }, { "cell_type": "code", "execution_count": 19, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "6" ] }, "execution_count": 19, "metadata": {}, "output_type": "execute_result" } ], "source": [ "math.ceil(5.4)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "math.trunc(5.8)" ] }, { "cell_type": "code", "execution_count": 20, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ 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] }, "execution_count": 20, "metadata": {}, "output_type": "execute_result" } ], "source": [ "math.factorial(1e4)" ] }, { "cell_type": "code", "execution_count": 21, "metadata": { "collapsed": false }, "outputs": [ { "ename": "ValueError", "evalue": "math domain error", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mValueError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mmath\u001b[0m\u001b[1;33m.\u001b[0m\u001b[0msqrt\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;33m-\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m)\u001b[0m \u001b[1;31m# Epa!!\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mValueError\u001b[0m: math domain error" ] } ], "source": [ "math.sqrt(-1) # Epa!!" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Pero existe un módulo equivalente para operaciones sobre el dominio complejo" ] }, { "cell_type": "code", "execution_count": 22, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "1j" ] }, "execution_count": 22, "metadata": {}, "output_type": "execute_result" } ], "source": [ "import cmath\n", "cmath.sqrt(-1)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Y también, sabiendo por propiedad de la potencia, podriamos directamente hacer:" ] }, { "cell_type": "code", "execution_count": 23, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "(6.123233995736766e-17+1j)" ] }, "execution_count": 23, "metadata": {}, "output_type": "execute_result" } ], "source": [ "(-1)**0.5" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Todo es un \"objeto\"" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "En Python todo es un *objeto*, es decir, una *instancia* de un clase o tipo de datos. Los objetos no solo *guardan* valores (atributos) sino que que tienen acceso a *métodos*, es decir, traen acciones (funciones) que podemos ejecutar sobre esos valores, a veces requiriendo/permitiendo parámetros adicionales. \n", "\n", "Jupyter/IPython facilita conocer todos los atributos y métodos de un objeto mediante **instrospección**. Prueben escribir `resutado.` y apretar ``. Por ejemplo:" ] }, { "cell_type": "code", "execution_count": 25, "metadata": { "collapsed": false }, "outputs": [], "source": [ "resultado = 1 + 2j" ] }, { "cell_type": "code", "execution_count": 30, "metadata": { "collapsed": false }, "outputs": [], "source": [ "R = 4.2" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [ "R.is_integer" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Además del `TAB`, en una sesión interactiva de Jupyter, se puede obtener ayuda contextual para cualquier objeto (cualquier cosa!) haciendo `Shift + TAB` una o más veces, o agregando un signo de interrogación al final (`blah?`) y ejecutando" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [] }, { "cell_type": "markdown", "metadata": {}, "source": [ "En python \"puro\", estos comportamientos se logran con las funciones `dir()` y `help()`" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Para conocer la clase/tipo de cualquier objecto se usa `type`" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "En muchos casos, se puede convertir explícitamente (o \"castear\") tipos de datos. En particular, entre números:" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "##### Ejercicios\n", "\n", "1. Crear una variable llamada `magnitud` con un valor real. Definir otra variable compleja `intensidad` cuya parte real sea 1.5 veces `magnitud` y la parte imaginaria `0.3` veces `magnitud` + `1j`. Encontrar la raiz cuadrada de `intensidad`. \n", "\n", "2. Para calcular un [interés compuesto](https://es.wikipedia.org/wiki/Inter%C3%A9s_compuesto) se utiliza la fórmula\n", "\n", "$$ \\ C_F = C_I(1+r)^n $$\n", "\n", "Donde:\n", "\n", "* $ \\ C_F $ es el capital al final del enésimo período\n", "* $ \\ C_I $ es el capital inicial\n", "* $ \\ r $ es la tasa de interés expresada en tanto por uno (v.g., 4 % = 0,04) \n", "* $ \\ n $ es el número de períodos\n", "\n", "Codifique la fórmula en una celda y calcule el capital final para un depósito inicial de 10 mil pesos a una tasa del 1.2% mensual en 18 meses.\n", "\n", "\n", "3. Investigue, a través de la ayuda interactiva, el parámetro opcional de `int` y las funciones `bin`, `oct` y `hex`. Basado en esto exprese en base 2 la operación 1 << 2 y en base hexadecimal `FA1` * `O17` " ] }, { "cell_type": "code", "execution_count": 31, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "(0.9671066161343038+0.579046808963441j)" ] }, "execution_count": 31, "metadata": {}, "output_type": "execute_result" } ], "source": [ "magnitud = .4\n", "intensidad = 1.5 * magnitud + 1j*(0.3*magnitud + 1)\n", "cmath.sqrt(intensidad)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "int('10', 8)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Texto\n", "\n", "Una cadena o *string* es una **secuencia** de caracteres (letras, números, simbolos). Python 3 utiliza el estándar [unicode](http://es.wikipedia.org/wiki/Unicode). " ] }, { "cell_type": "code", "execution_count": 32, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Hola mundo!\n" ] } ], "source": [ "print(\"Hola mundo!\")" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "chinito = \"字漢字\"" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "type(chinito)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "De paso, `unicode` se aplica a todo el lenguaje, de manera que el propio código puede usar caracterés \"no ascii\"" ] }, { "cell_type": "code", "execution_count": 43, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "bytes" ] }, "execution_count": 43, "metadata": {}, "output_type": "execute_result" } ], "source": [ "type(b'hola')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las cadenas se pueden definir con apóstrofes, comillas, o triple comillas, de manera que es menos frecuente la necesidad de \"escapar\" caracteres" ] }, { "cell_type": "code", "execution_count": 44, "metadata": { "collapsed": false }, "outputs": [], "source": [ "calle = \"O'Higgings\"\n", "metáfora = 'Los \"patitos\" en fila'" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las triples comillas permiten crear cadenas multilínea" ] }, { "cell_type": "code", "execution_count": 45, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'Me gustas cuando \"callas\"\\nporque estás como ausente...'" ] }, "execution_count": 45, "metadata": {}, "output_type": "execute_result" } ], "source": [ "V = \"\"\"Me gustas cuando \"callas\"\n", "porque estás como ausente...\"\"\"\n", "V" ] }, { "cell_type": "code", "execution_count": 48, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'Me gustas cuando \"callas\"\\nporque estás como ausente...'" ] }, "execution_count": 48, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sdsd = Out[45]" ] }, { "cell_type": "code", "execution_count": 49, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Me gustas cuando \"callas\"\n", "porque estás como ausente...\n" ] } ], "source": [ "print(poema)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [ "poema." ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las cadenas tienen sus propios **métodos**: pasar a mayúsculas, capitalizar, reemplazar una subcadena, etc. " ] }, { "cell_type": "code", "execution_count": 55, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'Hola amigos'" ] }, "execution_count": 55, "metadata": {}, "output_type": "execute_result" } ], "source": [ "v = \"hola amigos\"\n", "v.capitalize()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las cadenas se pueden concatenar" ] }, { "cell_type": "code", "execution_count": 58, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'fue un soldado de San Martín'" ] }, "execution_count": 58, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = \"fue un soldado de San Martín\"\n", "a = a.title()" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "y repetir" ] }, { "cell_type": "code", "execution_count": 62, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'*fue un soldado de San Martín'" ] }, "execution_count": 62, "metadata": {}, "output_type": "execute_result" } ], "source": [ "\"*\" + a" ] }, { "cell_type": "code", "execution_count": 66, "metadata": { "collapsed": false }, "outputs": [ { "ename": "ValueError", "evalue": "invalid literal for int() with base 10: 'a'", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mValueError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"a\"\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mValueError\u001b[0m: invalid literal for int() with base 10: 'a'" ] } ], "source": [ "int(\"a\")" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Para separar una cadena se usa el método `split`" ] }, { "cell_type": "code", "execution_count": 73, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "['hola', 'amigos', 'como']" ] }, "execution_count": 73, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = \"hola,amigos,como\"\n", "\n", "a.split(',')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Y el método inverso es `join`, para unir muchas cadenas intercalandolas con otra" ] }, { "cell_type": "code", "execution_count": 76, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'yjugandoalamornosencontró'" ] }, "execution_count": 76, "metadata": {}, "output_type": "execute_result" } ], "source": [ "\" \".join(['y', 'jugando', 'al', 'amor', 'nos', 'encontró'])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Indizado y rebanado" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las cadenas son **secuencias**. O sea, conjuntos ordenados que se pueden indizar, recortar, reordenar, etc. \n", "\n", "![](/files/img/index_slicing.png)\n" ] }, { "cell_type": "code", "execution_count": 86, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'HL UD'" ] }, "execution_count": 86, "metadata": {}, "output_type": "execute_result" } ], "source": [ "cadena = \"HOLA MUNDO\"\n", "cadena[::2] " ] }, { "cell_type": "code", "execution_count": 87, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'ODNUM ALOH'" ] }, "execution_count": 87, "metadata": {}, "output_type": "execute_result" } ], "source": [ "cadena[::-1] #wow!" ] }, { "cell_type": "code", "execution_count": 81, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'HO'" ] }, "execution_count": 81, "metadata": {}, "output_type": "execute_result" } ], "source": [ "cadena[0:2]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "El tipo `str` en python es **inmutable**, lo que quiere decir que, una vez definido un objeto tipo cadena no podemos modificarlo. " ] }, { "cell_type": "code", "execution_count": 90, "metadata": { "collapsed": false }, "outputs": [ { "ename": "TypeError", "evalue": "'str' object does not support item assignment", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0mcadena\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;36m0\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m'B'\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mTypeError\u001b[0m: 'str' object does not support item assignment" ] } ], "source": [ "cadena[0] = 'B'" ] }, { "cell_type": "code", "execution_count": 92, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'BOLA MUNDO'" ] }, "execution_count": 92, "metadata": {}, "output_type": "execute_result" } ], "source": [ "'B' + cadena[1:]" ] }, { "cell_type": "code", "execution_count": 91, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'BOLA MUNDO'" ] }, "execution_count": 91, "metadata": {}, "output_type": "execute_result" } ], "source": [ "cadena = cadena.replace('H', 'B')\n", "cadena" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Pero si podemos basarnos en un string para crear otro" ] }, { "cell_type": "code", "execution_count": 93, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'BOLA SUBMUNDO'" ] }, "execution_count": 93, "metadata": {}, "output_type": "execute_result" } ], "source": [ "cadena[:4] + \" SUB\" + cadena[5:]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### longitud de una secuencia\n", "\n", "La función `len` (de *lenght*) devuelve la cantidad de elementos de cualquier secuencia" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "len(cadena)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### interpolación\n", "\n", "Se puede crear un string a partir de una \"plantilla\" con un formato predeterminado. La forma más poderosa es a través del método [`format`](https://docs.python.org/3.4/library/string.html#format-examples)" ] }, { "cell_type": "code", "execution_count": 94, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'hola mundo'" ] }, "execution_count": 94, "metadata": {}, "output_type": "execute_result" } ], "source": [ "\"%s mundo\" % \"hola\"" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "\"{saludo} {planeta}\".format(saludo='Hola', planeta='Mundo') # placeholders por nombre de argumentos" ] }, { "cell_type": "code", "execution_count": 102, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'La parte real es 1.00000 y la imaginaria es 2.0 (1+2j)'" ] }, "execution_count": 102, "metadata": {}, "output_type": "execute_result" } ], "source": [ "\"La parte real es {numero.real:.5f} y la imaginaria es {numero.imag} {numero}\".format(numero=resultado)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Casting de tipos\n", "\n", "Python es dinámico pero de **tipado es fuerte**. Quiere decir que no intenta adivinar lo que estamos intentando hacer y nos exige ser explícitos." ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "\"2\" + \"2\"" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "int(\"2\") + int(\"2\")" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "\n", "float('2.34545') ** 2" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ejercicios\n", "\n", "\n", "1. Dado un texto cualquiera, crear uno equivalente con \"subrayado\" con el caracter \"=\" en toda su longitud . Por ejemplo, `\"Beso a Beso\"`, se debe imprimir por pantalla\n", "\n", " ===========\n", " Beso a Beso\n", " ===========\n", "\n", "2. Dada una cadena de palabras separadas por coma, generar otra cadena multilinea de \"items\" que comienzan por `\"* \"`. Por ejemplo \"manzanas, naranjas, bananas\" debe imprimir:\n", "\n", " * manzanas\n", " * naranjas\n", " * bananas\n" ] }, { "cell_type": "code", "execution_count": 105, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Beso a Beso me enamoré\n", "======================\n", "\n" ] } ], "source": [ "cadena = \"Beso a Beso me enamoré\"\n", "longitud = len(cadena)\n", "subrayado = \"=\" * longitud\n", "print(\"\"\"{}\n", "{}\n", "\"\"\".format(cadena, subrayado))" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [ "%timeit?" ] }, { "cell_type": "code", "execution_count": 104, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Beso a Beso me enamoré\n", "======================\n" ] } ], "source": [ "cadena = \"Beso a Beso me enamoré\"\n", "longitud = len(cadena)\n", "subrayado = \"=\" * longitud\n", "\n", "print(cadena + '\\n' + subrayado)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "\"b, a, c\".split(', ')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "----\n", "\n", "### Listas y tuplas: contenedores universales" ] }, { "cell_type": "code", "execution_count": 106, "metadata": { "collapsed": false }, "outputs": [], "source": [ "nombres = [\"Melisa\", \"Nadia\", \"Daniel\"]" ] }, { "cell_type": "code", "execution_count": 107, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "list" ] }, "execution_count": 107, "metadata": {}, "output_type": "execute_result" } ], "source": [ "type(nombres)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las listas tambien son secuencias, por lo que el indizado y rebanado funciona igual" ] }, { "cell_type": "code", "execution_count": 110, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "'Daniel'" ] }, "execution_count": 110, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nombres[-1]" ] }, { "cell_type": "code", "execution_count": 111, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "['Nadia', 'Daniel']" ] }, "execution_count": 111, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nombres[-2:]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Y pueden contener cualquier tipo de objetos" ] }, { "cell_type": "code", "execution_count": 112, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mezcolanza = [1.2, \"Jairo\", 12e6, calle, nombres[1]]" ] }, { "cell_type": "code", "execution_count": 113, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[1.2, 'Jairo', 12000000.0, \"O'Higgings\", 'Nadia']\n" ] } ], "source": [ "print(mezcolanza)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Hasta acá son iguales a las **tuplas**" ] }, { "cell_type": "code", "execution_count": 114, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "\n", "(1.2, (1j, 'Melisa'))\n" ] }, { "data": { "text/plain": [ "('Martín', 1.2, (1j, 'Melisa'))" ] }, "execution_count": 114, "metadata": {}, "output_type": "execute_result" } ], "source": [ "una_tupla = (\"Martín\", 1.2, (1j, nombres[0]))n\n", "print(type(una_tupla))\n", "print(una_tupla[1:3])\n", "una_tupla" ] }, { "cell_type": "code", "execution_count": 124, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "['Martín', 1.2, (1j, 'Melisa')]" ] }, "execution_count": 124, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(una_tupla)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "**LA DIFERENCIA** es que las **listas son mutables**. Es decir, es un objeto que puede cambiar: extenderse con otra secuencia, agregar o quitar elementos, cambiar un elemento o una porción por otra, reordenarse *in place*, etc. " ] }, { "cell_type": "code", "execution_count": 119, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mezcolanza.extend([1,2])\n", "mezcol" ] }, { "cell_type": "code", "execution_count": 120, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[1.2,\n", " 'Jairo',\n", " 12000000.0,\n", " \"O'Higgings\",\n", " 'Nadia',\n", " 'otro elemento',\n", " 'otro elemento',\n", " 'otro elemento',\n", " [1, 2],\n", " 1,\n", " 2]" ] }, "execution_count": 120, "metadata": {}, "output_type": "execute_result" } ], "source": [ "mezcolanza" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "una_tupla.append('a')" ] }, { "cell_type": "code", "execution_count": 121, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mezcolanza[0] = \"otra cosa\"" ] }, { "cell_type": "code", "execution_count": 122, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "['otra cosa',\n", " 'Jairo',\n", " 12000000.0,\n", " \"O'Higgings\",\n", " 'Nadia',\n", " 'otro elemento',\n", " 'otro elemento',\n", " 'otro elemento',\n", " [1, 2],\n", " 1,\n", " 2]" ] }, "execution_count": 122, "metadata": {}, "output_type": "execute_result" } ], "source": [ "mezcolanza" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Incluso se pueden hacer asignaciones de secuencias sobres \"slices\"" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mezcolanza[0:2] = ['A', 'B'] # notar que no hace falta que el valor tenga el mismo tamaño que el slice\n", "mezcolanza" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Como las tuplas son inmutables (como las cadenas), no podemos hacer asignaciones" ] }, { "cell_type": "code", "execution_count": 123, "metadata": { "collapsed": false }, "outputs": [ { "ename": "TypeError", "evalue": "'tuple' object does not support item assignment", "output_type": "error", "traceback": [ "\u001b[1;31m---------------------------------------------------------------------------\u001b[0m", "\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)", "\u001b[1;32m\u001b[0m in \u001b[0;36m\u001b[1;34m()\u001b[0m\n\u001b[1;32m----> 1\u001b[1;33m \u001b[0muna_tupla\u001b[0m\u001b[1;33m[\u001b[0m\u001b[1;33m-\u001b[0m\u001b[1;36m1\u001b[0m\u001b[1;33m]\u001b[0m \u001b[1;33m=\u001b[0m \u001b[1;34m\"osooo\"\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m", "\u001b[1;31mTypeError\u001b[0m: 'tuple' object does not support item assignment" ] } ], "source": [ "una_tupla [-1] = \"osooo\"" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las **tuplas** son mucho más eficientes (y seguras) si sólo vamos a **leer** elementos. Pero muchas operaciones son comunes. " ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "l = [1, 3, 4, 1]\n", "t = (1, 3, 1, 4)\n", "print(l.count(3))\n", "print(t.count(3))\n", "l.append('8')\n", "l" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### packing/unpacking\n", "\n", "Como toda secuencia, las listas y tuplas se pueden *desempacar*" ] }, { "cell_type": "code", "execution_count": 125, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Juan se sacó un 10\n" ] } ], "source": [ "nombre, nota = (\"Juan\", 10)\n", "print(\"{} se sacó un {}\".format(nombre, nota)) # igual a \"{0} se sacó un {1}\"" ] }, { "cell_type": "code", "execution_count": 126, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "2.0\n" ] } ], "source": [ "a, b = 1, 2.0\n", "a, b = b, a\n", "print (a)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Python 3 permite un desempacado extendido" ] }, { "cell_type": "code", "execution_count": 128, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "(1, 2, [3, 4, 5])\n", "(1, [3, 4], 5)\n" ] } ], "source": [ "a, b, *c = (1, 2, 3, 4, 5)\n", "print((a, b, c))\n", "\n", "a, *b, c = [1, 2, 3, 4, 5]\n", "print((a, b, c))" ] }, { "cell_type": "code", "execution_count": 129, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "1 [2, 3, 4] 5\n" ] } ], "source": [ "v = [1, 2, 3, 4, 5]\n", "a, b, c = (v[0], v[1:-1], v[-1])\n", "print(a, b, c)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Como con los números, se pueden convertir las secuencias de un tipo de dato a otro. Por ejemplo:" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "a = (1, 3, 4)\n", "list(('A', 1))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Una función *builtin* muy útil es `range`" ] }, { "cell_type": "code", "execution_count": 135, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[3, 5, 7, 9]" ] }, "execution_count": 135, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(range(3, 10, 2))" ] }, { "cell_type": "code", "execution_count": 138, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "range(0, 6)" ] }, "execution_count": 138, "metadata": {}, "output_type": "execute_result" } ], "source": [ "range(6)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "range(-10, 10)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "range(0, 25, 5)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "También hay una función estándar que da la sumatoria" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "help(sum)" ] }, { "cell_type": "code", "execution_count": 139, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "21.36" ] }, "execution_count": 139, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sum([1, 5.36, 5, 10])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "En toda secuencia tenemos el método index, que devuelve la posición en la que se encuentra un elemento" ] }, { "cell_type": "code", "execution_count": 140, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "1" ] }, "execution_count": 140, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a = [1, 'hola', []]\n", "a.index('hola')" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "y como las listas son *mutables* también se pueden reordenar *in place* (no se devuelve un valor, se cambia sobre la misma variable)" ] }, { "cell_type": "code", "execution_count": 146, "metadata": { "collapsed": false }, "outputs": [], "source": [ "a = [1, 2, 3]\n", "a.reverse()" ] }, { "cell_type": "code", "execution_count": 147, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[3, 2, 1]" ] }, "execution_count": 147, "metadata": {}, "output_type": "execute_result" } ], "source": [ "a" ] }, { "cell_type": "code", "execution_count": 149, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[1, 2, 3]" ] }, "execution_count": 149, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(reversed(a))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "La forma alternativa es usando una función, que **devuelve** un valor" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "b = list(reversed(a))\n", "b" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "
*Nota*: se fuerza la conversión de tipo con `list()` porque reversed no devuelve estrictamente una lista. Ya veremos más sobre esto.
\n", "\n", "Una función útil es `zip()`, que agrupa elementos de distintas secuencias" ] }, { "cell_type": "code", "execution_count": 151, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[('Juan', 'cerveza', 'arg'), ('Martín', 'boca juniors', 'chi')]" ] }, "execution_count": 151, "metadata": {}, "output_type": "execute_result" } ], "source": [ "nombres = ['Juan', 'Martín', 'María']\n", "pasiones = ['cerveza', 'boca juniors', 'lechuga', 1]\n", "nacionalidad = ('arg', 'chi',)\n", "list(zip(nombres, pasiones, nacionalidad))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ejercicios\n", "\n", "1. Resuelva la siguiente operación $$\\frac{(\\sum_{k=0}^{100}k)^3}{2}$$\n", "\n", "2. Dada cualquier secuencia, devolver una tupla con sus elementos concatenados en a la misma secuencia en orden inverso. Por ejemplo para `\"ABCD\"` devuelve `('A', 'B', 'C', 'D', 'D', 'C', 'B', 'A')`\n", "\n", "3. Generar dos listas a partir de la funcion `range` de 10 elementos, la primera con los primeros multiplos de 2 a partir de 0 y la segunda los primeros multiplos de 3 a partir de 30 (inclusive). Devolver como una lista de tuplas\n", "`[(0, 30), (2, 33),... ]`\n" ] }, { "cell_type": "code", "execution_count": 154, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "64393812500.0" ] }, "execution_count": 154, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sum(range(0, 101))**3/2" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "t = list(\"ABCD\")\n", "tuple(t + list(reversed(t)))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Estructuras de control de flujos\n", "\n", "#### if/elif/else\n", "\n", "En todo lenguaje necesitamos controlar el flujo de una ejecución segun una condición Verdadero/Falso (booleana). *Si (condicion) es verdadero hacé (bloque A); Sino hacé (Bloque B)*. En pseudo código:\n", "\n", " Si (condicion):\n", " bloque A\n", " sino:\n", " bloque B\n", "\n", "y en Python es muy parecido! \n" ] }, { "cell_type": "code", "execution_count": 156, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "edad: 1\n", "Usted es menor de edad. Raje de acá, pendejo\n" ] } ], "source": [ "edad = int(input('edad: '))\n", "if edad < 18:\n", " \n", " print(\"Usted es menor de edad. Raje de acá, pendejo\") \n", "else:\n", " print(\"Bienvenido, jovatón\")\n" ] }, { "cell_type": "code", "execution_count": 159, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "True" ] }, "execution_count": 159, "metadata": {}, "output_type": "execute_result" } ], "source": [] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Los operadores lógicos en Python son muy explicitos. \n", " \n", " A == B \n", " A > B \n", " A < B\n", " A >= B\n", " A <= B\n", " A != B\n", " A in B\n", "\n", "* A todos los podemos combinar con `not`, que niega la condición\n", "* Podemos combinar condiciones con `AND` y `OR`, las funciones `all` y `any` y paréntesis" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Podemos tener multiples condiciones en una estructura. Se ejecutará el primer bloque cuya condición sea verdadera, o en su defecto el bloque `else`. Esto es equivalente a la sentencia `switch` o `select case` de otros lenguajes " ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "if edad < 12:\n", " print(\"Feliz dia del niño\")\n", "elif 13 < edad < 18:\n", " print(\"Qué problema los granitos, no?\")\n", "elif edad in range(19, 90):\n", " print(\"No seré feliz pero tengo marido\") \n", "else:\n", " print(\"Y eso es todo amigos!\")" ] }, { "cell_type": "code", "execution_count": 162, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "False" ] }, "execution_count": 162, "metadata": {}, "output_type": "execute_result" } ], "source": [ "all([True, False, True])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "En un `if`, la conversión a tipo *boolean* es implícita. El tipo `None` (vacío), el `0`, una secuencia (lista, tupla, string) (o conjunto o diccionario, que ya veremos) vacía siempre evalua a ``False``. Cualquier otro objeto evalua a ``True``." ] }, { "cell_type": "code", "execution_count": 163, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "Dio cero\n" ] } ], "source": [ "a = 5 - 5\n", "\n", "if a: \n", " a = \"No es cero\"\n", "else: \n", " a = \"Dio cero\"\n", "print(a)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Para hacer asignaciones condicionales se puede usar la *estructura ternaria* del `if`: `A si (condicion) sino B`" ] }, { "cell_type": "code", "execution_count": 165, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "No es cero\n" ] } ], "source": [ "b = 5 - 6\n", "a = \"No es cero\" if b else \"dio cero\"\n", "print(a)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ejercicio\n", "\n", "dados **valores** numéricos para a, b y c, implementar la formula d $x = \\frac{-b \\pm \\sqrt {b^2-4ac}}{2a}$\n", "\n", "donde a, b y c son lo coeficientes de la ecuación $ax^2 + bx + c = 0, \\quad \\mbox{para}\\;a\\neq 0$" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### For\n", "\n", "Otro control es **iterar** sobre una secuencia (o *\"iterador\"*). Obtener cada elemento para hacer algo. En Python se logra con la sentencia `for`\n" ] }, { "cell_type": "code", "execution_count": 166, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "6.6" ] }, "execution_count": 166, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sumatoria = 0\n", "for elemento in [1, 2, 3.6]:\n", " sumatoria = sumatoria + elemento\n", "sumatoria" ] }, { "cell_type": "code", "execution_count": 167, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[(0, 'a'), (1, 'b'), (2, 'c')]" ] }, "execution_count": 167, "metadata": {}, "output_type": "execute_result" } ], "source": [ "list(enumerate(['a', 'b', 'c']))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Notar que no iteramos sobre el índice de cada elemento, sino sobre los elementos mismos. ¡Basta de `i`, `j` y esas variables innecesarias! . Si por alguna razon son necesarias, tenemos la función `enumerate`\n" ] }, { "cell_type": "code", "execution_count": 168, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "El valor de la posicion 0 es 4\n", "El valor de la posicion 1 es 3\n", "El valor de la posicion 2 es 19\n" ] } ], "source": [ "for (posicion, valor) in enumerate([4, 3, 19]):\n", " print(\"El valor de la posicion %s es %d\" % (posicion, valor))" ] }, { "cell_type": "code", "execution_count": 169, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "0\n", "1\n", "2\n", "3\n", "4\n", "5\n", "6\n", "7\n", "8\n", "9\n" ] } ], "source": [ "for i in range(10):\n", " print(i)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "El bloque `for` se corre hasta el final del *iterador* o hasta encontrar un sentencia `break`" ] }, { "cell_type": "code", "execution_count": 170, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "(5050, 101)" ] }, "execution_count": 170, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sumatoria = 0\n", "for elemento in range(1000):\n", " if elemento > 100:\n", " break\n", " sumatoria = sumatoria + elemento\n", "sumatoria, elemento" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "También podemos usar `continue` para omitir la ejecución de \"una iteración\"" ] }, { "cell_type": "code", "execution_count": 171, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "0\n", "2\n", "4\n", "6\n", "8\n", "10\n", "12\n", "14\n", "16\n", "18\n" ] }, { "data": { "text/plain": [ "90" ] }, "execution_count": 171, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sumatoria = 0\n", "for elemento in range(20):\n", " if elemento % 2:\n", " continue\n", " print(elemento)\n", " sumatoria = sumatoria + elemento\n", "sumatoria" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Muchas veces queremos iterar una lista para obtener otra, con sus elementos modificados. Por ejemplo, obtener una lista con los cuadrados de los primeros 10 enteros." ] }, { "cell_type": "code", "execution_count": 172, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "[9, 4, 1, 0, 1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196]\n" ] } ], "source": [ "cuadrados = []\n", "for i in range(-3,15,1):\n", " cuadrados.append(i**2)\n", "print (cuadrados)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Una forma compacta y elegante (¡pythónica!) de escribir esta estructura muy frecuente son las **listas por comprehensión**:" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "guardado = [i**2 for i in range(-3,15,1) if i % 2]" ] }, { "cell_type": "code", "execution_count": 173, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "[0, 2, 4, 6, 8]" ] }, "execution_count": 173, "metadata": {}, "output_type": "execute_result" } ], "source": [ "[n*2 for n in range(5)]" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Se lee: \"Obtener el cuadrado de cada elemento i de la secuencia (rango 0 a 9)\". Pero además podemos filtrar: usar solo los elementos que cumplen una condición. \n", "\n", "#### Ejercicios\n", "\n", "1. Obtener la sumatoria de los cubos de los numeros impares menores a 100. $$\\sum_{a=0}^{100}a^3 \\mid a\\ impar $$\n", "\n", "2. Obtener la productoria de los primeros 12 digitos decimales de PI\n", "3. Encuentre el mínimo de $$f(x) = (x-4)^2-3 \\mid x \\in [-100, 100)$$ \n", "4. Encuentre el promedio de los números reales de la cadena `\"3,4 1,2 -6 0 9,7\"`" ] }, { "cell_type": "code", "execution_count": 177, "metadata": { "collapsed": false }, "outputs": [ { "data": { "text/plain": [ "12497500" ] }, "execution_count": 177, "metadata": {}, "output_type": "execute_result" } ], "source": [ "sum(a**3 for a in range(101) if a % 2 != 0)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "import math\n", "sum([int(digito) for digito in str(math.pi)[2:14]])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Expresiones generadores\n", "\n", "Al crear una lista por comprehensión, se calculan todos los valores y se agregan uno a uno a la lista, que una vez completa se \"devuelve\" como un objeto nuevo. \n", "\n", "Cuando no necesitamos todos los valores *al mismo tiempo*, porque por ejemplo podemos consumirlos de 1 en 1, es mejor crear *generadores*, que son tipos de datos **iterables pero no indizables** (es el mismo tipo de objeto que devuelve `reversed`, que ya vimos)." ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "sum(a**2 for a in range(10))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### While\n", "\n", "Otro tipo de sentencia de control es *while*: iterar mientras se cumpla una condición" ] }, { "cell_type": "code", "execution_count": 180, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "ingrese un numero3\n", "3\n", "4\n", "5\n", "6\n", "7\n", "8\n", "9\n" ] } ], "source": [ "a = int(input('ingrese un numero'))\n", "while a < 10:\n", " print (a)\n", " a += 1" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Como en la iteración con `for` se puede utilizar la sentencia `break` para \"romper\" el bucle. Entonces puede modificarse para que la condición esté en una posicion arbitraria" ] }, { "cell_type": "code", "execution_count": 181, "metadata": { "collapsed": false }, "outputs": [ { "name": "stdout", "output_type": "stream", "text": [ "2 elefantes se balanceaban sobre la tela de una araña\n", "Desea invitar a otro elefante?si\n", "3 elefantes se balanceaban sobre la tela de una araña\n", "Desea invitar a otro elefante?si\n", "4 elefantes se balanceaban sobre la tela de una araña\n", "Desea invitar a otro elefante?s\n", "5 elefantes se balanceaban sobre la tela de una araña\n", "Desea invitar a otro elefante?no\n" ] } ], "source": [ "n = 1\n", "while True:\n", " n = n + 1\n", " print('{} elefantes se balanceaban sobre la tela de una araña'.format(n))\n", " continuar = input('Desea invitar a otro elefante?')\n", " if continuar == 'no':\n", " break" ] }, { "cell_type": "markdown", "metadata": {}, "source": [] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "min" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Diccionarios\n", "\n", "La diccionarios son otro tipo de estructuras de alto nivel que ya vienen incorporados. A diferencia de las secuencias, los valores **no están en una posición** sino bajo **una clave**: son asociaciones `clave:valor`\n" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "camisetas = {'Orión': 1, 'Carlitos': 10, 'Gago': 5, 'Gaitán': 'Jugador nº 12'} " ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Accedemos al valor a traves de un clave" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "camisetas['Perez'] = 8" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "camisetas" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Las claves pueden ser cualquier objeto inmutable (cadenas, numeros, tuplas) y los valores pueden ser cualquier tipo de objeto. Las claves no se pueden repetir pero los valores sí.\n", "\n", "**Importante**: los diccionarios **no tienen un orden definido**. Si por alguna razón necesitamos un orden, debemos obtener las claves, ordenarlas e iterar por esa secuencia de claves ordenadas.\n" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "sorted(camisetas.keys(), reverse=True)" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Los diccionarios **son mutables**. Es decir, podemos cambiar el valor de una clave, agregar o quitar. " ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "list(camisetas.items())" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Hay muchos *métodos* útiles" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "for jugador, camiseta in camisetas.items():\n", " if jugador == 'Gaitán':\n", " continue \n", " print(\"%s lleva la %d\" % (jugador, camiseta))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Se puede crear un diccionario a partir de tuplas `(clave, valor)` a traves de la propia clase `dict()`" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "dict([('Yo', 'gaitan@gmail.com'), ('Melisa', 'mgomez@phasety.com'), ('Cismondi', 'cismondi@phasety.com')])" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Que es muy útil usar con la función `zip()` que ya vimos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "nombres = (\"Martin\", \"Mariano\")\n", "emails = (\"tin@email.com\", \"nano@email.com\")\n", "\n", "dict(zip(nombres, emails))" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ejercicio\n", "\n", "#. Dados la lista de precios por kilo:\n", "\n", " precios = {\n", " \"banana\": 12,\n", " \"manzana\": 8.5,\n", " \"naranja\": 6,\n", " \"pera\": 18\n", " }\n", "\n", " Y la siguiente lista de compras \n", "\n", " compras = {\n", " \"banana\": 1,\n", " \"naranja\": 3,\n", " \"pera\": 0,\n", " \"manzana\": 1\n", " }\n", "\n", " Calcule el costo total de la compra. \n", "\n", "\n", "#. Ejecute `import this` y luego analice el código del módulo con `this??` . ¿comprende el algoritmo? Cree el algoritmo inverso, es decir, codificador de [rot13](https://es.wikipedia.org/wiki/ROT13)\n" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "import this" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [ "this??" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "### Conjuntos\n", "\n", "Los conjuntos (`set()` o `{}`) son grupos de elementos únicos. Al igual que los diccionarios, no están necesariamente ordenados" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos = set(['perro', 'gato', 'leon'])\n", "domesticos = {'perro', 'gato', 'gallina'}\n", "aves = {'gallina', 'halcón', 'colibrí'}" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Los conjuntos tienen métodos para cada una de las operaciones del [álgebra de conjuntos](https://es.wikipedia.org/wiki/%C3%81lgebra_de_conjuntos)" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos.intersection(domesticos) # mamiferos & domesticos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos.union(domesticos) # mamiferos | domesticos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "aves.difference(domesticos) # mamiferos - domesticos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos.symmetric_difference(domesticos) # mamiferos ^ domesticos" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Se puede comparar pertenencia de elementos y subconjuntos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "'gato' in mamiferos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "domesticos.issubset(mamiferos) " ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Además, tienen métodos para agregar o extraer elementos" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "mamiferos.add('elefante')\n", "mamiferos" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "Por supuesto, se puede crear un conjunto a partir de cualquier iterador" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "set([1, 2, 3, 2, 1, 3])" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [ "frozenset" ] }, { "cell_type": "markdown", "metadata": { "collapsed": true }, "source": [ "Existe también una **versión inmutable** de los diccionarios, llamado `frozenset`" ] }, { "cell_type": "markdown", "metadata": {}, "source": [ "#### Ejercicio\n", "\n", "La función `dir()` devuelve una lista con los nombre de todos los métodos y atributos de un objeto. Obtener una lista ordenada de los métodos en común entre `list`, `tuple` y `str` y los que son exclusivos para cada uno" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": false }, "outputs": [], "source": [ "a = [1]\n", "\n", "set(dir(list)) & set(dir(tuple)) & set(dir(str))" ] }, { "cell_type": "code", "execution_count": null, "metadata": { "collapsed": true }, "outputs": [], "source": [] } ], "metadata": { "kernelspec": { "display_name": "Python 3", "language": "python", "name": "python3" }, "language_info": { "codemirror_mode": { "name": "ipython", "version": 3 }, "file_extension": ".py", "mimetype": "text/x-python", "name": "python", "nbconvert_exporter": "python", "pygments_lexer": "ipython3", "version": "3.4.0" } }, "nbformat": 4, "nbformat_minor": 0 }