How to write a Python Regular Expression to validate numbers?

Here, we will learn how to write a regular expression for validating a number in Python. As you may know Python has a module called re module for working with regular expression easily using the built-in functions. The re.match() function matches or validate the regex pattern with the given number.

There are several ways to validate a number using regular expression, such as -

• Validate Integer Number
• Validate Real Number
• Validate Comma Separated Numbers

Example: Validate Integer Number

The following example will use different integer values to validate that they are numbers or not. We are using r"^[+-]?\d+$" pattern to validate whether a given string is an integer value.

The pattern ^[+-]? and \d will help us to match one or more digits with + or - signs. And re.match() will help us to match this pattern.

# Import re module
import re

# define different numbers
txt1 = "123"
txt2 = "-456"
txt3 = "123nick"

# define regex pattern
pat = r"^[+-]?\d+$"

# create a function to match a number
def is_match(txt):
    # make sure txt is a string
    return bool(re.match(pat, str(txt)))  

# Print the result
print(is_match(txt1))  
print(is_match(txt2))  
print(is_match(txt3))  

Output

This will create the below outcome -

True
True
False

Example: Validate Real Number

This is another easy way to check if a given number is a real number or not. Here the pattern we have used is r"^[+-]?\d+(\.\d+)?$", in which pattern ^[+-]? and \d will work same as the above example but the pattern \. will look for a decimal point followed by digits.

# Import re module
import re

# define different numbers
txt1 = "3.14"
txt2 = "-2.71"
txt3 = "123"
txt4 = "abc"

# define regex pattern
pat = r"^[+-]?\d+(\.\d+)?$"

# create a function to match a number
def is_match(txt):
    # make sure txt is a string
    return bool(re.match(pat, str(txt)))  

# print the result
print(is_match(txt1))  
print(is_match(txt2))  
print(is_match(txt3))
print(is_match(txt4))  

Output

This will generate the below result -

True
True
True
False

Example: Validate Comma Separated Numbers

In the below program we are using the r"^[+-]?(\d{1,3}(,\d{3})*+)(\.\d+)?$" pattern to check that the given string shows a comma separated numbers or not.

The pattern (\d{1,3}(,\d{3})*|\d+) is used to make sure numbers are present with commas like "1,234" or "1,234.56".

# Import re module
import re

# define comma separated numbers
txt1 = "5,456.98"
txt2 = "236235632"
txt3 = "-2,568"
txt4 = "34,24"

# define regex pattern
pat = r"^[+-]?(\d{1,3}(,\d{3})*+)(\.\d+)?$"

# create a function to match a number
def is_match(txt):
    # make sure txt is a string
    return bool(re.match(pat, str(txt)))  

# print the result
print(is_match(txt1))  
print(is_match(txt2))  
print(is_match(txt3))
print(is_match(txt4))  

Output

This will produce the following result -

True
True
True
False