How to check if a variable is a number in Python?

Question

Jayant Kumar · Accepted Answer

Table of Contents
Introduction
In Python, determining whether a variable is a number is a common requirement, especially when dealing with numeric data input or performing type-specific operations. Python supports various numeric types including integers, floating-point numbers, and complex numbers. This guide explores different methods for checking if a variable is a number and provides practical examples for each method.
Methods to Check if a Variable is a Number
1. Using **isinstance()** Function

**int** Type Check: To check if a variable is an integer, use isinstance() with the int type.
**float** Type Check: To check if a variable is a floating-point number, use isinstance() with the float type.
**complex** Type Check: To check if a variable is a complex number, use isinstance() with the complex type.
Checking for Any Numeric Type: To check if a variable is any of the numeric types (integer, float, or complex), combine multiple isinstance() checks.

Example:
# Sample variables
var1 = 42
var2 = 3.14
var3 = 2 + 3j
var4 = "Hello"

# Check if variables are numbers
print(isinstance(var1, int))    # Output: True
print(isinstance(var2, float))  # Output: True
print(isinstance(var3, complex))# Output: True
print(isinstance(var4, (int, float, complex)))  # Output: False

2. Using **type()** Function

Direct Type Check: You can use the type() function to check the exact type of a variable. This method is less flexible than isinstance() because it does not account for inheritance or multiple types.

Example:
# Sample variables
var1 = 42
var2 = 3.14
var3 = 2 + 3j

# Check the exact type of variables
print(type(var1) == int)    # Output: True
print(type(var2) == float)  # Output: True
print(type(var3) == complex)# Output: True

3. Using **isinstance()** with Tuple for Multiple Types

Checking for Multiple Numeric Types: Use isinstance() with a tuple of types to check if a variable is any of the numeric types. This method is efficient and concise for type checking.

Example:
# Sample variables
var1 = 42
var2 = 3.14
var3 = 2 + 3j
var4 = "Hello"

# Check if variables are any numeric type
print(isinstance(var1, (int, float, complex)))  # Output: True
print(isinstance(var2, (int, float, complex)))  # Output: True
print(isinstance(var3, (int, float, complex)))  # Output: True
print(isinstance(var4, (int, float, complex)))  # Output: False

4. Using **try-except** for Conversion

Handling String Inputs: When dealing with user input or strings, you might need to try converting the input to a number and catch exceptions if the conversion fails. This method is useful for dynamic input validation.

Example:
def is_number(value):
    try:
        float(value)  # Attempt to convert to float
        return True
    except ValueError:
        return False

# Sample inputs
print(is_number("123"))   # Output: True
print(is_number("12.34")) # Output: True
print(is_number("abc"))   # Output: False

Practical Examples
Example : Checking Variable Type in Function
def check_number(value):
    if isinstance(value, (int, float, complex)):
        print(f"{value} is a number.")
    else:
        print(f"{value} is not a number.")

# Sample values
check_number(10)        # Output: 10 is a number.
check_number(3.14)      # Output: 3.14 is a number.
check_number("text")    # Output: text is not a number.

Example : Validating User Input
def get_numeric_input(prompt):
    while True:
        user_input = input(prompt)
        if is_number(user_input):
            return float(user_input)  # Convert to float if valid
        else:
            print("Invalid input. Please enter a valid number.")

# Prompt for user input
number = get_numeric_input("Enter a number: ")
print(f"You entered: {number}")

Conclusion
Checking if a variable is a number in Python can be achieved using various methods, including isinstance(), type(), and try-except for conversions. The isinstance() function is versatile and useful for checking against multiple numeric types, while type() provides exact type checking. For dynamic input, converting strings and handling exceptions ensures robust validation. Understanding these methods helps in accurately identifying numeric data and handling different types of inputs effectively.

How to check if a variable is a number in Python?

Table of Contents

Introduction

Methods to Check if a Variable is a Number

1. Using `isinstance()` Function

Example:

2. Using `type()` Function

Example:

3. Using `isinstance()` with Tuple for Multiple Types

Example:

4. Using `try-except` for Conversion

Example:

Practical Examples

Example : Checking Variable Type in Function

Example : Validating User Input

Conclusion

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