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How to Check if a String is a Float in Python

Last Updated : April 28, 2025

In Python, a string can often be converted into an integer or a float. However, checking if a string can be interpreted as a valid float requires specific approaches. In this chapter, we will explore multiple methods to verify if a string is a float in Python.

Checking String is Float Using try-except with float() Function

You can convert a string to a float using the float() function inside a try-except block to check if it is a valid float.

Example

This example demonstrates using exception handling to check for float conversion.

def is_float(s):
    try:
        float(s)
        return True
    except ValueError:
        return False

# Test cases
print(is_float("123.456"))  # True
print(is_float("abc"))      # False

The output of the above code would be:

True
False

Checking String is Float Using str.replace() and str.isdigit()

You can remove a decimal point from the string and use isdigit() to check if the remaining characters are all digits.

Example

This example demonstrates validating float format manually by checking for a single decimal point.

def is_float(s):
    if s.count('.') == 1:
        s = s.replace('.', '')
        return s.isdigit()
    return False

# Test cases
print(is_float("123.456"))  # True
print(is_float("123.45.6")) # False
print(is_float("abc"))      # False

The output of the above code would be:

True
False
False

Checking String is Float Using Regular Expressions (Regex)

You can use the re module with a regular expression pattern to check if a string matches the float format.

Example

This example demonstrates using regular expressions to match valid float patterns in strings.

import re

def is_float(s):
    pattern = r'^-?\d*(\.\d+)?$'
    return bool(re.match(pattern, s))

# Test cases
print(is_float("123.456"))  # True
print(is_float("-123.456")) # True
print(is_float("123."))     # False
print(is_float("abc"))      # False

The output of the above code would be:

True
True
False
False

Checking String is Float Using str.isnumeric() with Additional Checks

You can combine isnumeric() and manual decimal checks to create a simple float validator for basic cases.

Example

This example demonstrates a numeric check after removing one decimal point.

def is_float(s):
    if s.replace('.', '', 1).isnumeric() and s.count('.') < 2:
        return True
    return False

# Test cases
print(is_float("123.456"))  # True
print(is_float("123"))      # True
print(is_float("12.34.56")) # False

The output of the above code would be:

True
True
False

Exercise

Select the correct option to complete each statement about checking if a string is a float in Python.

1. One simple way to check if a string can be converted to a float is to use a ___ block. --Select-- try-except if-else for-while
2. Inside the try block, you attempt to convert the string using the ___ function. --Select-- str float int
3. If a string cannot be converted to a float, a ___ exception is typically raised. --Select-- ValueError TypeError KeyError