Check user Input is a Number or String in Python

In this lesson, you will learn how to check user input is a number or string in Python. We will also cover how to accept numbers as input from the user. When we say a number, it means it can be integer or float.

Understand user input

Python 3 has a built-in function input() to accept user input. But it doesn’t evaluate the data received from the input() function, i.e., The input() function always converts the user input into a string and then returns it to the calling program.

Let us understand this with an example.

number1 = input("Enter number and hit enter ")
print("Printing type of input value")
print("type of number ", type(number1))

Output
Enter number and hit enter 10
Printing type of input value
type of number class 'str'

As you can see, The output shows the type of a variable as a string (str).

Solution: In such a situation, We need to convert user input explicitly to integer and float to check if it’s a number. If the input string is a number, It will get converted to int or float without exception.

Convert string input to int or float to check if it is a number

Note: If an input is an integer or float number, it can successfully get converted to int or float, and you can conclude that entered input is a number. Otherwise, You get a valueError exception, which means the entered user input is a string.

Program :

def check_user_input(input):
    try:
        # Convert it into integer
        val = int(input)
        print("Input is an integer number. Number = ", val)
    except ValueError:
        try:
            # Convert it into float
            val = float(input)
            print("Input is a float  number. Number = ", val)
        except ValueError:
            print("No.. input is not a number. It's a string")


input1 = input("Enter your Age ")
check_user_input(input1)

input2 = input("Enter any number ")
check_user_input(input2)

input2 = input("Enter the last number ")
check_user_input(input2)

Output

Enter your Age 28
Input is an integer number. Number =  28

Enter any number 3.14
Input is a float  number. Number =  3.14

Enter the last number 28Jessa
No.. input is not a number. It's a string

• As you can see in the above output, the user has entered 28, and it gets converted into the integer type without exception.
• Also, when the user entered 3.14, and it gets converted into the float type without exception.
• But when the user entered a number with some character in it (28Jessa), Python raised a ValueError exception because it is not int.

Use string isdigit() method to check user input is number or string

Note: The isdigit() function will work only for positive integer numbers. i.e., if you pass any float number, it will not work. So, It is better to use the first approach.

Let’s execute the program to validate this.

def check_is_digit(input_str):
    if input_str.strip().isdigit():
        print("User input is Number")
    else:
        print("User input is string")


num1 = input("Enter number and hit enter")
check_is_digit(num1)

num2 = input("Enter number and hit enter")
check_is_digit(num2)

Output

Enter number and hit enter 45
User input is Number

Enter number and hit enter 45Jessa
User input is string

Also, If you can check whether the Python variable is a number or string, use the isinstance() function.

Example

num = 25.75
print(isinstance(num, (int, float)))
# Output True

num = '28Jessa'
print(isinstance(num, (int, float)))
# Output False

Only accept a number as input

Let’s write a simple program in Python to accept only numbers input from the user. The program will stop only when the user enters the number input.

while True:
    num = input("Please enter a number ")
    try:
        val = int(num)
        print("Input is an integer number.")
        print("Input number is: ", val)
        break;
    except ValueError:
        try:
            float(num)
            print("Input is an float number.")
            print("Input number is: ", val)
            break;
        except ValueError:
            print("This is not a number. Please enter a valid number")

Output

Please enter a number 28Jessa
This is not a number. Please enter a valid number

Please enter a number 28
Input is an integer number.
Input number is:  28

Practice Problem: Check user input is a positive number or negative

user_number = input("Enter your number ")

print("\n")
try:
    val = int(user_number)
    if val > 0:
        print("User number is positive ")
    else:
        print("User number is negative ")
except ValueError:
    print("No.. input string is not a number. It's a string")

Next Steps

Let me know your comments and feedback in the section below.

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• Python input and output exercise
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