3 Ways to Check if String contains Number in Python

Summary: In this programming tutorial, we will learn different ways to check if the given string has any character as a number in Python.

Method 1: Using for loop with str.isdigit()

The isdigit() is a built-in string method in Python that returns True if all the characters of the given strings are integer.

To check whether the given string has integers, we will loop through its characters using a for loop and use the isdigit method on each character.

>>> string = 'python123'
>>> for x in string:
...     if x.isdigit():
...         print('String has integers.')
...         break
String has integers

Alternatively, we can rewrite the same code using any() function as follows:

>>> string = 'python123'
>>> result = any(x.isdigit() for x in string)
>>> print(result)
True

Method 2: Using map() with str.isdigit()

The map(function, iterator) functions in Python apply the given function to each item of the given iterator and returns the resultant iterator.

If we apply str.isdigit to each character of the string using the map function, we will get the resultant iterator (i.e. map object) that may contain True as one of its items, if any of the characters in the given string is an integer.

>>> string = 'python123'
>>> result = any(map(str.isdigit, string))
>>> print(result)
True

Method 3: Using Regular Expression

The fastest way to check if a string contains numbers is through regular expressions.

The re.search(r'\d', string) function looks for the pattern r'\d' (i.e. integer) in the given string and returns the match object if a match is found. Otherwise, it returns None.

If the match object returned by the search function is not None, the string has numbers.

>>> import re
>>>
>>> string = 'ak5647'
>>> match = re.search(r'\d', string)
>>> if match:
...     print('Yes')
... else:
...     print('No')
Yes

We can make this process more efficient and faster by using re.compile() on the pattern before the re.search() function (when the expression will be used several times in a single program).

In that case, we call the search method on the object returned by the re.compile function with the string parameter.

>>> import re
>>>
>>> string = 'ak5647'
>>>
>>> re_obj = re.compile(r'\d')
>>> match = re_obj.search(string)
>>>
>>> if match:
...     print('Yes')
... else:
...     print('No')
Yes

In conclusion, we can easily check for the numbers in a string in Python by using the isdigit(), any() or map() function, and regular expression. However, using regular expression is efficient in the case of larger strings.