Python – Extract Strings with a digit

Given a Strings List, extract those with atleast one digit.

Input : test_list = [‘gf4g’, ‘is’, ‘best’, ‘gee1ks’] 
Output : [‘gf4g’, ‘gee1ks’] 
Explanation : 4, 1 are respective digits in string.

Input : test_list = [‘gf4g’, ‘is’, ‘best’, ‘neveropen’] 
Output : [‘gf4g’] 
Explanation : 4 is digit in string. 

Method #1 : Using list comprehension + any() + isdigit()

In this iteration for each string is done using list comprehension, any() and isdigit() is used for task of checking at least one digit.

step by step approach:

1. Initialize the input list test_list with some string values.
2. Print the original list.
3. Create a list comprehension using sub as the loop variable to iterate over each element sub in test_list.
4. For each element sub in test_list, use the any() function to check if any character in the string is a digit using the isdigit() method.
5. If the above condition is true, append the element sub to the result list res.
6. Print the list of strings with digits.

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n²)
Space Complexity: O(n)

Method #2 : Using any() + filter() + lambda

In this, we perform task of filtering using lambda and filter(), rest remains the same.

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n²) 
Space Complexity: O(n)

Method #3 : Without any builtin methods

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n*n) where n is the number of elements in the list “test_list”. 
Auxiliary Space: O(n) additional space of size n is created where n is the number of elements in the list “test_list”. 

Method #4 : Using ord() function

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(N*M)

Auxiliary Space: O(1)

Method 5 : Using regular expressions
In this approach, we use the re.search() function from the re module which searches for a pattern in the given string. The pattern ‘\d’ represents a digit in the string. The function returns a match object if there is a match and None otherwise. Hence, for every string in the list, we check if there is a digit present by calling re.search(‘\d’, i) where i is the current string in the list. If there is a match, we add the string i to the resultant list. Finally, the resultant list is returned which has all the strings containing at least one digit.

The original list is : ['gf4g', 'is', 'best', '4', 'gee1ks']
Strings with any digit : ['gf4g', '4', 'gee1ks']

Time Complexity: O(n)
Auxiliary Space: O(n)