Using a For or While Loop to take user input in Python

# Table of Contents

1. Using a for loop to take user input in Python
2. While loop with user Input in Python

# Using a for loop to take user input in Python

To use a for loop to take user input:

1. Declare a new variable and initialize it to an empty list.
2. Use the range() class to loop N times in a for loop.
3. On each iteration, append the input value to the list.

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my_list = []

for _ in range(3):
    my_list.append(input('Enter a country: '))

print(my_list)

The first example takes multiple string inputs from a user and appends them to a list.

We used the range() class to iterate 3 times in a for loop and prompt the user for input on each iteration.

The range() class is commonly used for looping a specific number of times in for loops and takes the following arguments:

If you only pass a single argument to the range() constructor, it is considered to be the value for the stop parameter.

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for n in range(3):
    print(n)

result = list(range(3))

# 👇️ [0, 1, 2]
print(result)

# Using a for loop to take integer user input

If you need to take integer values from user input in a for loop, use the int() class to convert each value.

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my_list = []

for _ in range(3):
    try:
        my_list.append(int(input('Enter a number: ')))
    except ValueError:
        print('The provided value is not an integer')


print(my_list)

The input() function takes an optional prompt argument and writes it to standard output without a trailing newline.

The function then reads the line from the input, converts it to a string and returns the result.

We used a try/except statement to handle the ValueError that is raised if the int() class is called with a value that is not a valid integer.

# Using a list comprehension instead of a for loop

Alternatively, you can use a list comprehension.

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my_list = [input('Enter a color: ') for _ in range(3)]

print(my_list)
# ----------------------------------------------

my_list = [int(input('Enter a number: ')) for _ in range(3)]

print(my_list)

The examples use a list comprehension to take multiple inputs from a user.

On each iteration, the user gets prompted for input.

Note that we can't use a try/except statement for validation in a list comprehension.

# While loop with user Input in Python

To take user input in a while loop:

1. Use a while loop to iterate until a condition is met.
2. Use the input() function to take user input.
3. If the condition is met, break out of the while loop.

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# 👇️ while loop with user input strings

password = ''

while True:
    password = input('Enter your password: ')

    if len(password) < 4:
        print('Password too short')
        continue
    else:
        print(f'You entered {password}')
        break

print(password)

The first example uses a while loop to iterate until the provided value has a length of at least 4 characters.

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password = ''

while True:
    password = input('Enter your password: ')

    if len(password) < 4:
        print('Password too short')
        continue
    else:
        print(f'You entered {password}')
        break

print(password)

If the value is at least 4 characters long, we use the break statement as the input is valid.

The continue statement continues with the next iteration of the loop.

The break statement breaks out of the innermost enclosing for or while loop.

If the input is valid, we use the break statement to exit out of the while loop.

# Using a while loop to take numeric input

You can use the same approach when validating numeric input.

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num = 0

while True:
    try:
        num = int(input("Enter an integer 1-5: "))
    except ValueError:
        print("Please enter a valid integer 1-5")
        continue
    if num >= 1 and num <= 5:
        print(f'You entered: {num}')
        break
    else:
        print('The integer must be in the range 1-5')

We used a while loop to iterate until the provided input value is in a specified range.

If the try block completes successfully, then the user entered an integer.

If the integer is not in the specified range, the else block runs and prints a message.

If the user didn't enter an integer, the except block runs, where we use the continue statement to prompt the user again.

# Additional Resources

You can learn more about the related topics by checking out the following tutorials:

• For or While loop to print Numbers from 1 to 10 in Python
• Using multiple variables in a For loop in Python
• Remove elements from a List while iterating in Python
• RuntimeError: This event loop is already running [Solved]
• EOFError: EOF when reading a line in Python [Solved]
• How to restart a Loop in Python