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      User Input

      Python Tutorial

      This Python tutorial has been written for the beginners to help them understand the basic to advanced concepts of Python Programming Language. After completing this tutorial, you will find yourself at a great level of expertise in Python, from where you can take yourself to the next levels to become a world class Software Engineer.

      User Input

      Provide User Input in Python

      In this chapter, we will learn how Python accepts the user input from the console, and displays the output on the same console.
      Every computer application should have a provision to accept input from the user when it is running. This makes the application interactive. Depending on how it is developed, an application may accept the user input in the form of text entered in the console (sys.stdin), a graphical layout, or a web-based interface.

      Python User Input Functions

      Python provides us with two built-in functions to read the input from the keyboard.
      • The input () Function
      • The raw_input () Function
      Python interpreter works in interactive and scripted mode. While the interactive mode is good for quick evaluations, it is less productive. For repeated execution of same set of instructions, scripted mode should be used.
      Let us write a simple Python script to start with.
      #! /usr/bin/python3.11
      
      name = "Kiran"
      city = "Hyderabad"
      
      print ("Hello My name is", name)
      print ("I am from", city)
      Save the above code as hello.py and run it from the command-line. Here's the output
      C:\python311> python hello.py
      Hello My name is Kiran
      I am from Hyderabad
      The program simply prints the values of the two variables in it. If you run the program repeatedly, the same output will be displayed every time. To use the program for another name and city, you can edit the code, change name to say "Ravi" and city to "Chennai". Every time you need to assign different value, you will have to edit the program, save and run, which is not the ideal way.

      The input() Function

      Obviously, you need some mechanism to assign different value to the variable in the runtime − while the program is running. Python's input() function does the same job.
      Following is the syntax of Python's standard library input() function.
      >>> var = input()
      When the interpreter encounters input() function, it waits for the user to enter data from the standard input stream (keyboard) till the Enter key is pressed. The sequence of characters may be stored in a string variable for further use.
      On reading the Enter key, the program proceeds to the next statement. Let use change our program to store the user input in name and city variables.
      #! /usr/bin/python3.11
      
      name = input()
      city = input()
      
      print ("Hello My name is", name)
      print ("I am from ", city)
      When you run, you will find the cursor waiting for user's input. Enter values for name and city. Using the entered data, the output will be displayed.
      Ravi
      Chennai
      Hello My name is Ravi
      I am from Chennai
      Now, the variables are not assigned any specific value in the program. Every time you run, different values can be input. So, your program has become truly interactive.
      Inside the input() function, you may give a prompt text, which will appear before the cursor when you run the code.
      #! /usr/bin/python3.11
      
      name = input("Enter your name : ")
      city = input("Enter your city : ")
      
      print ("Hello My name is", name)
      print ("I am from ", city)
      When you run the program displays the prompt message, basically helping the user what to enter.
      Enter your name: Praveen Rao
      Enter your city: Bengaluru
      Hello My name is Praveen Rao
      I am from Bengaluru

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.
      

      The raw_input() Function

      The raw_input() function works similar to input() function. Here only point is that this function was available in Python 2.7, and it has been renamed to input() in Python 3.6
      Following is the syntax of the raw_input() function:
      >>> var = raw_input ([prompt text])
      Let's re-write the above program using raw_input() function:
      #! /usr/bin/python3.11
      
      name = raw_input("Eneter your name - ")
      city = raw_input("Enter city name - ")
      
      print ("Hello My name is", name)
      print ("I am from ", city)
      When you run, you will find the cursor waiting for user's input. Enter values for name and city. Using the entered data, the output will be displayed.
      Eneter your name - Ravi
      Enter city name - Chennai
      Hello My name is Ravi
      I am from Chennai

      Taking Numeric Input in Python

      Let us write a Python code that accepts width and height of a rectangle from the user and computes the area.
      #! /usr/bin/python3.11
      
      width = input("Enter width : ")
      height = input("Enter height : ")
      
      area = width*height
      print ("Area of rectangle = ", area)
      Run the program, and enter width and height.
      Enter width: 20
      Enter height: 30
      Traceback (most recent call last):
        File "C:\Python311\var1.py", line 5, in <module>
         area = width*height
      TypeError: can't multiply sequence by non-int of type 'str'
      Why do you get a TypeError here? The reason is, Python always read the user input as a string. Hence, width="20" and height="30" are the strings and obviously you cannot perform multiplication of two strings.
      To overcome this problem, we shall use int(), another built-in function from Python's standard library. It converts a string object to an integer.
      To accept an integer input from the user, read the input in a string, and type cast it to integer with int() function
      w = input("Enter width : ")
      width = int(w)
      
      h = input("Enter height : ")
      height = int(h)
      You can combine the input and type cast statements in one
      #! /usr/bin/python3.11
      
      width = int(input("Enter width : "))
      height = int(input("Enter height : "))
      
      area = width*height
      print ("Area of rectangle = ", area)
      Now you can input any integer value to the two variables in the program
      Enter width: 20
      Enter height: 30
      Area of rectangle = 600
      Python's float() function converts a string into a float object. The following program accepts the user input and parses it to a float variable − rate, and computes the interest on an amount which is also input by the user.
      #! /usr/bin/python3.11
      
      amount = float(input("Enter Amount : "))
      rate = float(input("Enter rate of interest : "))
      
      interest = amount*rate/100
      print ("Amount: ", amount, "Interest: ", interest)
      The program ask user to enter amount and rate; and displays the result as follows
      Enter Amount: 12500
      Enter rate of interest: 6.5
      Amount: 12500.0 Interest: 812.5

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.
      

      The print() Function

      Python's print() function is a built-in function. It is the most frequently used function, that displays value of Python expression given in parenthesis, on Python's console, or standard output (sys.stdout).
      print ("Hello World ")
      Any number of Python expressions can be there inside the parenthesis. They must be separated by comma symbol. Each item in the list may be any Python object, or a valid Python expression.
      #! /usr/bin/python3.11
      
      a = "Hello World"
      b = 100
      c = 25.50
      d = 5+6j
      print ("Message: a)
      print (b, c, b-c)
      print(pow(100, 0.5), pow(c,2))
      The first call to print() displays a string literal and a string variable. The second prints value of two variables and their subtraction. The pow() function computes the square root of a number and square value of a variable.
      Message Hello World
      100 25.5 74.5
      10.0 650.25
      If there are multiple comma separated objects in the print() function's parenthesis, the values are separated by a white space " ". To use any other character as a separator, define a sep parameter for the print() function. This parameter should follow the list of expressions to be printed.
      In the following output of print() function, the variables are separated by comma.
      #! /usr/bin/python3.11
      
      city="Hyderabad"
      state="Telangana"
      country="India"
      print(city, state, country, sep=',')
      The effect of sep=',' can be seen in the result
      Hyderabad,Telangana,India
      The print() function issues a newline character ('\n') at the end, by default. As a result, the output of the next print() statement appears in the next line of the console.
      city="Hyderabad"
      state="Telangana"
      print("City:", city)
      print("State:", state)
      Two lines are displayed as the output
      City: Hyderabad
      State: Telangana
      To make these two lines appear in the same line, define end parameter in the first print() function and set it to a whitespace string " ".
      city="Hyderabad"
      state="Telangana"
      country="India"
      
      print("City:", city, end=" ")
      print("State:", state)
      Output of both the print() functions appear in continuation.
      City: Hyderabad State: Telangana

      Practice with Online Editor

      Note: This Python online Editor is a Python interpreter written in Rust, RustPython may not fully support all Python standard libraries and third-party libraries yet.
      Remember to save code(Ctrl + S Or Command + S) before run it.