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      "[Python for Developers](http://ricardoduarte.github.io/python-for-developers/#content)\n",
      "===================================\n",
      "First edition\n",
      "-----------------------------------\n",
      "\n",
      "Chapter 3: Control Flow\n",
      "=============================\n",
      "_____________________________\n",
      "It is very common for a program that certain sets of instructions are executed conditionally, in cases such as validating data entries, for example.\n",
      "\n",
      "Syntax:\n",
      "\n",
      "    if <condition>:\n",
      "        <code block>\n",
      "    elif <condition>:\n",
      "        <code block>\n",
      "    elif <condition>:\n",
      "        <code block>\n",
      "    else:\n",
      "        <code block>\n",
      "\n",
      "Where:\n",
      "\n",
      "+ `<condition>`: sentence that can be evaluated as true or false.\n",
      "+ `<code block>`: sequence of command lines.\n",
      "+ The clauses `elif` and `else` are optional and\u00a0 several `elifs` for the `if` may be used but only\u00a0 one `else` at the end.\n",
      "+ Parentheses are only required to avoid ambiguity.\n",
      "Example:"
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      "temp = 23 # temperature value used to test\n",
      "\n",
      "if temp < 0:\n",
      "    print 'Freezing...'\n",
      "elif 0 <= temp <= 20:\n",
      "    print 'Cold'\n",
      "elif 21 <= temp <= 25:\n",
      "    print 'Normal'\n",
      "elif 26 <= temp <= 35:\n",
      "    print 'Hot'\n",
      "else:\n",
      "    print 'Very Hot!'"
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        "Normal\n"
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      "Imagine that in the above program, `23` is the temperature which was read by\u00a0 some sensor or manually entered by the user and `Normal` is the response of the program.\n",
      "\n",
      "If the code block is composed of only one line, it can be written after the colon:\n",
      "\n",
      "    if temp < 0: print 'Freezing...'\n",
      "\n",
      "Since version 2.5, Python supports the expression:\n",
      "\n",
      "    <variable> = <value 1> if <condition> else <value 2>\n",
      "\n",
      "Where `<variable>` receives `<value 1>` if `<condition>` is true and `<value 2>`  otherwise."
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