Check Whether String Contains Only Numbers or Not - Python

We are given a string s="12345" we need to check whether the string contains only number or not if the string contains only number we will return True or if the string does contains some other value then we will return False. This article will explore various techniques to check if a string contains only numbers including simple string methods regular expressions, and other useful approaches.

Using str.isdigit()

str.isdigit() method in Python is a straightforward way to check if a string contains only numeric characters, this method is especially useful for validating input or extracting numeric data from strings during data processing.

s = "12345"

# Check if the string contains only numbers
b = s.isdigit()

print(b)

True

Explanation:

• str.isdigit() checks whether all characters in the string are numeric returning True if the string contains only digits and False otherwise.
• In this example since the string "12345" consists solely of numeric characters, str.isdigit() returns True, confirming the string is entirely numeric.

Using Regular Expressions (re.fullmatch)

re.fullmatch() method is a powerful way to verify if an entire string follows a specific pattern, it allows precise control over pattern matching such as ensuring a string contains only numeric characters.

import re

s = "12345"

# Check if the string contains only numbers using regex
b = bool(re.fullmatch(r'\d+', s))

print(b)

True

Explanation:

• Code uses re.fullmatch(r'\d+', s) to check if the entire string s matches the regular expression \d+, which ensures the string contains one or more digits (\d represents a digit).
• Result of re.fullmatch is converted to a boolean using bool(), returning True if the string contains only numbers and False otherwise

Using str.replace()

str.replace() method in Python allows us to replace specific characters or substrings within a string with another value.

s = "123.45"

# Check if the string contains only numbers and a single decimal point
b = s.replace('.', '', 1).isdigit()

print(b)

True

Explanation:

• str.replace() is used to remove the first occurrence of a decimal point (.) from the string, allowing strings with only one decimal point to pass validation. After this, it checks if the remaining string is numeric using isdigit().
• If the modified string contains only digits, the isdigit() method returns True indicating the input string represents a valid numeric value (with at most one decimal point).

Using all()

To check if a string contains only digits or numeric values, we can use the all() function combined with str.isdigit()

s = "12345"

# Check if all characters are digits
b = all(char.isdigit() for char in s)

print(b)

True

Explanation:

• all() checks if all elements in an iterable are True. In this case, it verifies if every character in the string is a digit using the isdigit() method.
• If all characters in the string are digits it returns True, otherwise it returns False. In this case, since "12345" consists entirely of digits, the result is True