How to Check if a String Contains Only Numbers in Python

Checking whether a string contains only numbers is a common task when dealing with strings that need to represent numerical data. Python offers several methods to achieve this, including isdigit, isnumeric, and even regular expressions. This article will explore each method with practical examples and real-world applications.

Method 1: Using isdigit

The isdigit method is straightforward and checks whether all characters in the string are digits.

Define a sample string:

my_string  "12345"

Here's how you can check if the string contains only digits using isdigit:

def contains_only_digits(s):    return ()test_string1  "12345"test_string2  "12345a"if contains_only_digits(test_string1):    print("The string contains only digits.")else:    print("The string does not contain only digits.")if contains_only_digits(test_string2):    print("The string contains only digits.")else:    print("The string does not contain only digits.")

Output:

The string contains only  string does not contain only digits.

Method 2: Using isnumeric

The isnumeric method is similar to isdigit, but it can handle more numeric characters, such as Unicode characters used in international numerals.

def is_numeric(s):    return ()test_string1  "12345"test_string2  "?????"  # Arabic numeralsprint(is_numeric(test_string1))   # Trueprint(is_numeric(test_string2))   # True

Note that isnumeric can handle non-decimal digits and numeric symbols that are not strictly digits, which makes it more versatile.

Method 3: Using Regular Expressions (Regex)

If you need a more powerful solution, you can use regular expressions to ensure that the string contains only digits. The [0-9] pattern matches any digit character.

import redef contains_only_digits_regex(s):    return bool(re.fullmatch(r'd*', s))test_string1  "12345"test_string2  "12345a"print(contains_only_digits_regex(test_string1))   # Trueprint(contains_only_digits_regex(test_string2))   # False

Output:

TrueFalse

Using all and a Character Check

Another approach is to iterate over the string and check each character to see if it is a digit. If any character is not a digit, the method returns False.

def is_digits_only(s):    return all(() for c in s)some_string  "12345"if is_digits_only(some_string):    print("The string contains only digits.")else:    print("The string does not contain only digits.")

Output:

The string contains only digits.

Catching Errors with int

A simpler but less robust approach is to try converting the string to an integer. If the string contains non-digit characters, the conversion will fail, and an exception will be raised.

str1  "45O2T"try:    int(str1)    print(f"{str1} only contains numbers")except ValueError:    print(f"{str1} comprises of values other than numbers")correct_str  "12345"if all(() or char in '-.' for char in correct_str):    print(f"{correct_str} contains only digits")else:    print(f"{correct_str} contains non-digit characters")

Output:

45O2T comprises of values other than numbers12345.0 contains only digits

Conclusion

Python provides multiple methods to check if a string contains only digits, ranging from simple and direct to more powerful and flexible approaches. The choice of method depends on the specific needs of your application and the type of strings you are working with. Whether you are dealing with basic integer representations or more complex numeric strings, these methods provide a solid foundation to ensure data integrity.