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‎Python_args_and_kwargs.ipynb

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{
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"cells": [
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"<small><small><i>\n",
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"All the IPython Notebooks in this lecture series by Dr. Milan Parmar are available @ **[GitHub](https://github.com/milaan9/07_Python_Advanced_Topics)**\n",
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"</i></small></small>"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"# Python __`*args`__ and __`**kwargs`__\n",
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"\n",
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"In this class, we will learn about Python __`*args`__ and __`**kwargs`__ ,their uses and functions with examples."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"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",
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"\n",
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"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",
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"\n",
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"Suppose, we define a function for addition of 3 numbers."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 1,
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"metadata": {
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"ExecuteTime": {
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"end_time": "2021-07-31T13:08:44.472274Z",
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"start_time": "2021-07-31T13:08:44.459576Z"
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},
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"scrolled": false
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"sum: 46\n"
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]
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}
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],
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"source": [
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"# Example 1: Function to add 3 numbers\n",
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"\n",
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"def adder(x,y,z):\n",
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" print(\"sum:\",x+y+z)\n",
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"\n",
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"adder(12,15,19)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"**Explanation:**\n",
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"\n",
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"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."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"Lets see what happens when we pass more than 3 arguments in the **`adder()`** function."
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]
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},
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{
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"cell_type": "code",
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"execution_count": 2,
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"metadata": {
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"ExecuteTime": {
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"end_time": "2021-07-31T13:08:44.903013Z",
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"start_time": "2021-07-31T13:08:44.475203Z"
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},
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"scrolled": true
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},
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"outputs": [
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{
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"ename": "TypeError",
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"evalue": "adder() takes 3 positional arguments but 5 were given",
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"output_type": "error",
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"traceback": [
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"\u001b[1;31m---------------------------------------------------------------------------\u001b[0m",
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"\u001b[1;31mTypeError\u001b[0m Traceback (most recent call last)",
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"\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",
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"\u001b[1;31mTypeError\u001b[0m: adder() takes 3 positional arguments but 5 were given"
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]
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}
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],
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"source": [
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"def adder(x,y,z):\n",
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" print(\"sum:\",x+y+z)\n",
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"\n",
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"adder(5,10,15,20,25)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"**Explanation:**\n",
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"\n",
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"In the above program, we passed 5 arguments to the **`adder()`** function instead of 3 arguments due to which we got **`TypeError`**."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Introduction to __`*args`__ and __`**kwargs`__ in Python\n",
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"\n",
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"In Python, we can pass a variable number of arguments to a function using special symbols. There are two special symbols:\n",
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"\n",
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"* __`*args`__ (Non Keyword Arguments)\n",
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"* __`**kwargs`__ (Keyword Arguments)\n",
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"\n",
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"We use __`*args`__ and __`**kwargs`__ as an argument when we are unsure about the number of arguments to pass in the functions."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Python __*args__\n",
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"\n",
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"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",
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"\n",
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"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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]
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},
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{
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"cell_type": "code",
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"execution_count": 3,
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"metadata": {
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"ExecuteTime": {
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"end_time": "2021-07-31T13:08:51.348994Z",
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"start_time": "2021-07-31T13:08:51.327507Z"
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}
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"Sum: 9\n",
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"Sum: 21\n",
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"Sum: 21\n"
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]
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}
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],
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"source": [
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"# Example 2: Using *args to pass the variable length arguments to the function\n",
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"\n",
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"def adder(*num):\n",
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" sum = 0\n",
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" \n",
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" for n in num:\n",
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" sum = sum + n\n",
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"\n",
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" print(\"Sum:\",sum)\n",
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"\n",
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"adder(3,6)\n",
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"adder(3,5,6,7)\n",
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"adder(1,2,3,6,9)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"**Explanation:**\n",
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"\n",
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"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."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Python __`**kwargs`__\n",
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"\n",
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"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",
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"\n",
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"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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]
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},
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{
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"cell_type": "code",
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"execution_count": 4,
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"metadata": {
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"ExecuteTime": {
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"end_time": "2021-07-31T13:08:57.897046Z",
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"start_time": "2021-07-31T13:08:57.871652Z"
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},
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"scrolled": true
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},
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"outputs": [
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{
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"name": "stdout",
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"output_type": "stream",
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"text": [
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"\n",
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"Data type of argument: <class 'dict'>\n",
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"Firstname is Amy\n",
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"Lastname is Barn\n",
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"Age is 24\n",
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"Phone is 1234567890\n",
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"\n",
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"Data type of argument: <class 'dict'>\n",
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"Firstname is Arthur\n",
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"Lastname is Hunt\n",
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"Email is [email protected]\n",
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"Country is Atlantis\n",
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"Age is 27\n",
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"Phone is 9976563219\n"
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]
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}
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],
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"source": [
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"# Example 3: Using **kwargs to pass the variable keyword arguments to the function \n",
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"\n",
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"def intro(**data):\n",
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" print(\"\\nData type of argument:\",type(data))\n",
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"\n",
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" for key, value in data.items():\n",
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" print(\"{} is {}\".format(key,value))\n",
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"\n",
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"intro(Firstname=\"Amy\", Lastname=\"Barn\", Age=24, Phone=1234567890)\n",
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"intro(Firstname=\"Arthur\", Lastname=\"Hunt\", Email=\"[email protected]\", Country=\"Atlantis\", Age=27, Phone=9976563219)"
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"**Explanation:**\n",
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"\n",
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"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.."
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]
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},
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{
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"cell_type": "markdown",
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"metadata": {},
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"source": [
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"## Things to Remember:\n",
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"\n",
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"* __`*args`__ and __`**kwargs`__ are special keyword which allows function to take variable length argument.\n",
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"* __`*args`__ passes variable number of non-keyworded arguments list and on which operation of the list can be performed.\n",
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"* __`**kwargs`__ passes variable number of keyword arguments dictionary to function on which operation of a dictionary can be performed.\n",
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"* __`*args`__ and __`**kwargs`__ make the function flexible."
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]
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},
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