1.6 Input data from Keyboard

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input

We used the print function to display program output. The input function is used to read user input from the keyboard. When the built-in-function input is called, the program stops and waits for the user to type from the keyboard. When the user presses Return or Enter, the program resumes and input returns what the user typed as a string data type by default.

1. Click + Code to add a code-cell
2. Type x = input
3. Type print(x)
4. Click play
5. Type the number 2 using your keyboard and press enter.

See code below

# x = input()
x = "2"   # ← web edition: the value the book's own run typed in
print(x)

2
2

Note: The value of input entered from the keyboard is stored in x

It is a good practice to print a prompt telling the user what to input. For example, input("what is your name?") will make it clear to the user what to enter. See code below.

1. Click + Code
2. Type x = input("What is your name? ")
3. Type print("Your name is", x)
4. Click play
5. Enter Don from your keyboard

# x = input("What is your name? ")
x = "Don"   # ← web edition: the value the book's own run typed in
print("Your name is",x)

What is your name? Don
Your name is Don

Note: The value of input entered by the user is stored in x. That is x = Don

Input Examples

Example: Write a Python program that accepts an integer $x$ and computes and prints the square-root of $x$. See code below.

# x = input("Enter any integer number: ")  #ask the user for a number
x = "5"   # ← web edition: the value the book's own run typed in
x = int(x)              # converts the input from string to integer (casting)
y = x**.5
print("The square-root is", y)

Enter any integer number: 5
The square-root is 2.23606797749979

Example: Write a Python program which asks the user for a radius of a circle and displays the area using the formula $A=\pi r^2$. See code below.

# r=input("Enter the radius of a circle: ")  #ask the user for radius
r = "6"   # ← web edition: the value the book's own run typed in
r=float(r)              # converts the string to float
import numpy      # we need the number pi 
area = numpy.pi*r**2
print("The area of the circle is", area,'square units')

Enter the radius of a circle: 6
The area of the circle is 113.09733552923255 square units

Example: Write a Python program to calculate adult body mass index for a given weight in pounds and height (feet and inches) using the formula, $BMI=703\frac{weight(lb)}{height(in{)}^2}$. See code below.

# w=input("Enter weight in pounds:")  #ask the user for a number
w = "60"   # ← web edition: the value the book's own run typed in
# h1 = input("Enter height feet only:")
h1 = "5"   # ← web edition: the value the book's own run typed in
# h2 = input("Enter inches:")
h2 = "2"   # ← web edition: the value the book's own run typed in
w,h1,h2 = float(w),float(h1),float(h2) # converts the number to float    
bmi = 703*(w/(h1*12+h2)**2)
print("The BMI is", bmi)

Enter weight in pounds:60
Enter height feet only:5
Enter inches:2
The BMI is 10.972944849115505

Adapted from Python for Introductory Statistics, by Simon Aman (Truman College, City Colleges of Chicago), licensed under CC BY 4.0. Changes were made: reformatted as an accessible XYZ web edition with live in-browser code cells. License: CC-BY-4.0.