How to Check if a Variable is a Number in Python?

When developing in Python, verifying whether a variable is a number is often necessary. Python provides several ways to check if a variable is a number. In this tutorial, I will show you different methods to check if a variable is a number in Python, along with examples and complete code.

To check if a variable is a number in Python using the isinstance() function, you can simply use the following code snippet: isinstance(variable, (int, float)). This checks if the variable is either an integer or a float. For example, isinstance(42, (int, float)) will return True, confirming that 42 is a number.

Check if a Variable is a Number in Python

Now, let me show you how to check if a variable is a number in Python using different methods.

Method 1: Using isinstance()

The isinstance() function is a built-in Python function that checks if a variable is a number in Python. This method can be used to check for multiple types at once.

Example-1:

Let me show you a few examples, starting with a basic example.

variable = 42

if isinstance(variable, (int, float)):
    print("The variable is a number.")
else:
    print("The variable is not a number.")

I executed the above Python code, and you can see the output in the screenshot below:

Now, let me show you another real-time example.

Suppose you are developing a temperature conversion app that converts Fahrenheit to Celsius. Before performing the conversion, you need to ensure that the user input is a number.

user_input = input("Enter the temperature in Fahrenheit: ")

try:
    temperature = float(user_input)
    if isinstance(temperature, (int, float)):
        celsius = (temperature - 32) * 5.0/9.0
        print(f"The temperature in Celsius is {celsius:.2f}")
except ValueError:
    print("Invalid input. Please enter a numeric value.")

Check out How to Check if a Variable is a Float in Python?

Method 2: Using type()

The type() function returns the type of an object. You can use the type() method to check if a variable is a number in Python.

Example-1:

Now, let me show you a simple example.

variable = 3.14

if type(variable) in (int, float):
    print("The variable is a number.")
else:
    print("The variable is not a number.")

You can see the output in the screenshot below after I executed the above Python code.

Example-2:

Here is another real-time example to help you understand it better.

Suppose you are building a system to check if a user is eligible to vote in the USA. You need to ensure the age entered is a number.

age_input = input("Enter your age: ")

try:
    age = int(age_input)
    if type(age) == int:
        if age >= 18:
            print("You are eligible to vote.")
        else:
            print("You are not eligible to vote.")
except ValueError:
    print("Invalid input. Please enter a numeric value.")

Read How to Check Variable Type is Boolean in Python?

Method 3: Using isnumeric(), isdigit(), and isdecimal()

These string methods can be used to check if a string represents a number in Python. Note that they work only for strings and do not recognize floating-point numbers or negative values.

Let me show you how to use methods like isnumeric(), isdigit(), and isdecimal() to check if a variable is a number in Python.

Example-1:

Here is a basic example.

variable = "12345"

if variable.isnumeric():
    print("The variable is a number.")
else:
    print("The variable is not a number.")

You can see the output in the screenshot below:

Example-2:

Now, let me show you another real-time example to help you understand better.

In the USA, ZIP codes are numeric and typically five digits long. These methods can be used to check if the input is a valid ZIP code.

zip_code = input("Enter your ZIP code: ")

if zip_code.isdigit() and len(zip_code) == 5:
    print("Valid ZIP code.")
else:
    print("Invalid ZIP code. Please enter a 5-digit numeric value.")

Read Check Type of Variable Is String in Python

Method 4: Using Regular Expressions

Regular expressions offer a powerful way to validate numbers, including integers and floating-point numbers in Python.

Now, let me show you some examples.

Example-1:

Here is a basic example to help you understand it better.

import re

variable = "123.45"
pattern = r'^\d+(\.\d+)?$'

if re.match(pattern, variable):
    print("The variable is a number.")
else:
    print("The variable is not a number.")

Example-2:

Here is another real-time example to help you understand it better.

Suppose you are developing a financial application that requires users to input dollar amounts. You can use regular expressions to validate the input.

import re

dollar_amount = input("Enter the dollar amount: ")
pattern = r'^\d+(\.\d{2})?$'

if re.match(pattern, dollar_amount):
    print("Valid dollar amount.")
else:
    print("Invalid dollar amount. Please enter a numeric value with up to two decimal places.")

Conclusion

In this tutorial, I have explained how to check if a variable is a number in Python using different methods such as: isinstance(), type(), isnumeric(), isdigit(), and isdecimal(), Regular Expressions, etc. I hope the above examples will be helpful to you.

You may also like the following tutorials:

• How to Check the Type of a Variable in Python?
• How to Check if a Variable is None in Python?
• How to Check Variable Type is datetime in Python?
• How to Change the Value of a Variable in Python?