How to write a Python regular expression that matches floating point numbers?

This article will discuss how to write a Python regular expression that matches floating point numbers. We will try to create a regular expression pattern that can match any floating point number.

A regular expression for floating point numbers should match integers and floating point numbers where the integer part might be optional. A floating-point number can look like ?

• Whole numbers with decimals like 3.14, 1.5, 12.10

• Negative numbers like -2.55, -1.003

• Numbers with optional zeros like 007.5, .75

Basic Regex Pattern for Floating Point Numbers

Here is the regular expression pattern for identifying floating point numbers ?

import re

# Basic pattern for floating point numbers
pattern = r"[+-]?[0-9]+\.[0-9]+"
print(f"Pattern: {pattern}")

Pattern: [+-]?[0-9]+\.[0-9]+

The above regex pattern components explained ?

• [+-]? − Optional plus (+) or minus (-) sign at the start
• [0-9]+ − At least one digit before the decimal point
• \. − The literal decimal point (escaped)
• [0-9]+ − At least one digit after the decimal point

Enhanced Pattern for More Cases

A more comprehensive pattern that handles edge cases like numbers starting with a decimal ?

import re

# Enhanced pattern that matches more floating point formats
enhanced_pattern = r"[+-]?(?:[0-9]*\.?[0-9]+)"

test_numbers = ["3.14", "-2.5", ".75", "42.", "+1.23", "007.5"]

for num in test_numbers:
    if re.fullmatch(enhanced_pattern, num):
        print(f"'{num}' is a valid floating point number")
    else:
        print(f"'{num}' is not matched")

'3.14' is a valid floating point number
'-2.5' is a valid floating point number
'.75' is a valid floating point number
'42.' is a valid floating point number
'+1.23' is a valid floating point number
'007.5' is a valid floating point number

Validate Floating Numbers in Text

Use re.findall() to extract all floating point numbers from a text string ?

import re

# Define a string with various numbers
text = "Pi is 3.14 and the temperature dropped to -2.5 degrees."

# Define pattern to match floating-point numbers
pattern = r"[+-]?[0-9]+\.[0-9]+"

# Find all matches in the string
matches = re.findall(pattern, text)

print("Floating point numbers found:", matches)

Floating point numbers found: ['3.14', '-2.5']

Validate User Input

Create a function to validate if user input is a valid floating point number ?

import re

def is_float(number_str):
    """Check if string represents a floating point number"""
    return bool(re.fullmatch(r"[+-]?[0-9]+\.[0-9]+", number_str))

# Test different inputs
test_inputs = ["12.5", "abc", "-3.14", "42", "1.0"]

for inp in test_inputs:
    result = is_float(inp)
    print(f"is_float('{inp}') = {result}")

is_float('12.5') = True
is_float('abc') = False
is_float('-3.14') = True
is_float('42') = False
is_float('1.0') = True

Extract Floating Numbers with Units

Extract floating point numbers that are followed by unit letters ?

import re

# String with numbers and units
text = "Measurements: 2.5kg, -1.75m, 50, 10.3cm, 15"

# Pattern to match floats followed by letters (units)
pattern = r"[+-]?[0-9]+\.[0-9]+(?=[a-z%])"

# Find floating numbers with units
numbers_with_units = re.findall(pattern, text)

print("Floating numbers with units:", numbers_with_units)

Floating numbers with units: ['2.5', '-1.75', '10.3']

Comparison of Patterns

Conclusion

Use [+-]?[0-9]+\.[0-9]+ for basic floating point validation. For comprehensive matching including edge cases, use the enhanced pattern. Combine with lookahead assertions when you need to match numbers with specific contexts like units.