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"<small><small><i>\n",
"All the IPython Notebooks in **Python Advanced Topics** lecture series by Dr. Milaan Parmar are available @ **[GitHub](https://github.com/milaan9/07_Python_Advanced_Topics)**\n",
"</i></small></small>"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"# Python __`*args`__ and __`**kwargs`__\n",
"\n",
"In this class, we will learn about Python __`*args`__ and __`**kwargs`__ ,their uses and functions with examples."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"In programming, we define a function to make a reusable code that performs similar operation. To perform that operation, we call a function with the specific value, this value is called a function argument in Python.\n",
"\n",
"We would recommend you to read **[Python Function](https://github.com/milaan9/04_Python_Functions/blob/main/001_Python_Functions.ipynb)** and **[Python Function Arguments](https://github.com/milaan9/04_Python_Functions/blob/main/004_Python_Function_Arguments.ipynb)**.\n",
"\n",
"Suppose, we define a function for addition of 3 numbers."
]
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"sum: 46\n"
]
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"source": [
"# Example 1: Function to add 3 numbers\n",
"\n",
"def adder(x,y,z):\n",
" print(\"sum:\",x+y+z)\n",
"\n",
"adder(12,15,19)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Explanation:**\n",
"\n",
"In above program we have **`adder()`** function with three arguments **`x`**, **`y`** and **`z`**. When we pass three values while calling **`adder()`** function, we get sum of the 3 numbers as the output."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"Lets see what happens when we pass more than 3 arguments in the **`adder()`** function."
]
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{
"ename": "TypeError",
"evalue": "adder() takes 3 positional arguments but 5 were given",
"output_type": "error",
"traceback": [
"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
"\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)",
"\u001b[1;32m<ipython-input-2-986e6d871071>\u001b[0m in \u001b[0;36m<module>\u001b[1;34m\u001b[0m\n\u001b[0;32m 2\u001b[0m \u001b[0mprint\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;34m\"sum:\"\u001b[0m\u001b[1;33m,\u001b[0m\u001b[0mx\u001b[0m\u001b[1;33m+\u001b[0m\u001b[0my\u001b[0m\u001b[1;33m+\u001b[0m\u001b[0mz\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0;32m 3\u001b[0m \u001b[1;33m\u001b[0m\u001b[0m\n\u001b[1;32m----> 4\u001b[1;33m \u001b[0madder\u001b[0m\u001b[1;33m(\u001b[0m\u001b[1;36m5\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;36m10\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;36m15\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;36m20\u001b[0m\u001b[1;33m,\u001b[0m\u001b[1;36m25\u001b[0m\u001b[1;33m)\u001b[0m\u001b[1;33m\u001b[0m\u001b[1;33m\u001b[0m\u001b[0m\n\u001b[0m",
"\u001b[1;31mTypeError\u001b[0m: adder() takes 3 positional arguments but 5 were given"
]
}
],
"source": [
"def adder(x,y,z):\n",
" print(\"sum:\",x+y+z)\n",
"\n",
"adder(5,10,15,20,25)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Explanation:**\n",
"\n",
"In the above program, we passed 5 arguments to the **`adder()`** function instead of 3 arguments due to which we got **`TypeError`**."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Introduction to __`*args`__ and __`**kwargs`__ in Python\n",
"\n",
"In Python, we can pass a variable number of arguments to a function using special symbols. There are two special symbols:\n",
"\n",
"* __`*args`__ (Non Keyword Arguments)\n",
"* __`**kwargs`__ (Keyword Arguments)\n",
"\n",
"We use __`*args`__ and __`**kwargs`__ as an argument when we are unsure about the number of arguments to pass in the functions."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Python __*args__\n",
"\n",
"As in the above example we are not sure about the number of arguments that can be passed to a function. Python has __`*args`__ which allow us to pass the variable number of non keyword arguments to function.\n",
"\n",
"In the function, we should use an asterisk **`*`** before the parameter name to pass variable length arguments.The arguments are passed as a tuple and these passed arguments make tuple inside the function with same name as the parameter excluding asterisk **`*`**."
]
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"name": "stdout",
"output_type": "stream",
"text": [
"Sum: 9\n",
"Sum: 21\n",
"Sum: 21\n"
]
}
],
"source": [
"# Example 2: Using *args to pass the variable length arguments to the function\n",
"\n",
"def adder(*num):\n",
" sum = 0\n",
" \n",
" for n in num:\n",
" sum = sum + n\n",
"\n",
" print(\"Sum:\",sum)\n",
"\n",
"adder(3,6)\n",
"adder(3,5,6,7)\n",
"adder(1,2,3,6,9)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Explanation:**\n",
"\n",
"In the above program, we used __`*num`__ as a parameter which allows us to pass variable length argument list to the **`adder()`** function. Inside the function, we have a loop which adds the passed argument and prints the result. We passed 3 different tuples with variable length as an argument to the function."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Python __`**kwargs`__\n",
"\n",
"Python passes variable length non keyword argument to function using __`*args`__ but we cannot use this to pass keyword argument. For this problem Python has got a solution called __`**kwargs`__, it allows us to pass the variable length of keyword arguments to the function.\n",
"\n",
"In the function, we use the double asterisk __`**`__ before the parameter name to denote this type of argument. The arguments are passed as a dictionary and these arguments make a dictionary inside function with name same as the parameter excluding double asterisk __`**`__."
]
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"text": [
"\n",
"Data type of argument: <class 'dict'>\n",
"Firstname is Amy\n",
"Lastname is Barn\n",
"Age is 24\n",
"Phone is 1234567890\n",
"\n",
"Data type of argument: <class 'dict'>\n",
"Firstname is Arthur\n",
"Lastname is Hunt\n",
"Email is arthurhunt@yesmail.com\n",
"Country is Atlantis\n",
"Age is 27\n",
"Phone is 9976563219\n"
]
}
],
"source": [
"# Example 3: Using **kwargs to pass the variable keyword arguments to the function \n",
"\n",
"def intro(**data):\n",
" print(\"\\nData type of argument:\",type(data))\n",
"\n",
" for key, value in data.items():\n",
" print(\"{} is {}\".format(key,value))\n",
"\n",
"intro(Firstname=\"Amy\", Lastname=\"Barn\", Age=24, Phone=1234567890)\n",
"intro(Firstname=\"Arthur\", Lastname=\"Hunt\", Email=\"arthurhunt@yesmail.com\", Country=\"Atlantis\", Age=27, Phone=9976563219)"
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"**Explanation:**\n",
"\n",
"In the above program, we have a function **`intro()`** with __`**data`__ as a parameter. We passed two dictionaries with variable argument length to the **`intro()`** function. We have for loop inside **`intro()`** function which works on the data of passed dictionary and prints the value of the dictionary.."
]
},
{
"cell_type": "markdown",
"metadata": {},
"source": [
"## Things to Remember:\n",
"\n",
"* __`*args`__ and __`**kwargs`__ are special keyword which allows function to take variable length argument.\n",
"* __`*args`__ passes variable number of non-keyworded arguments list and on which operation of the list can be performed.\n",
"* __`**kwargs`__ passes variable number of keyword arguments dictionary to function on which operation of a dictionary can be performed.\n",
"* __`*args`__ and __`**kwargs`__ make the function flexible."
]
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