# Python – Retain Numbers in String

• Last Updated : 05 Sep, 2022

Sometimes, while working with Python Strings, we can have a problem in which we need to perform the removal of all the characters other than integers. This kind of problem can have application in many data domains such as Machine Learning and web development. Let’s discuss certain ways in which this task can be performed.

Input : test_str = ‘G4g is No. 1’ Output : 41 Input : test_str = ‘Gfg is No. 1’ Output : 1

Method #1 : Using list comprehension + join() + isdigit() The combination of above functions can be used to solve this problem. In this, we perform the task of extracting integers using isdigit(), list comprehension is used for iteration and join() is used to perform join of numbers filtered.

## Python3

 `# Python3 code to demonstrate working of``# Retain Numbers in String``# Using list comprehension + join() + isdigit()` `# initializing string``test_str ``=` `'G4g is No. 1 for Geeks 7'` `# printing original string``print``(``"The original string is : "` `+` `str``(test_str))` `# Retain Numbers in String``# Using list comprehension + join() + isdigit()``res ``=` `"".join([ele ``for` `ele ``in` `test_str ``if` `ele.isdigit()])` `# printing result``print``(``"String after integer retention : "` `+` `str``(res))`

Output :

```The original string is : G4g is No. 1 for Geeks 7
String after integer retention : 417```

Method #2 : Using regex() The solution of problem can also be found by using regex. In this, we formulate appropriate regex to filter only numbers from string.

## Python3

 `# Python3 code to demonstrate working of``# Retain Numbers in String``# Using regex()``import` `re` `# initializing string``test_str ``=` `'G4g is No. 1 for Geeks 7'` `# printing original string``print``(``"The original string is : "` `+` `str``(test_str))` `# Retain Numbers in String``# Using regex()``res ``=` `re.sub(r``'[^\d]+'``, '', test_str)` `# printing result``print``(``"String after integer retention : "` `+` `str``(res))`

Output :

```The original string is : G4g is No. 1 for Geeks 7
String after integer retention : 417```

The Time and Space Complexity for all the methods are the same:

Time Complexity: O(n)

Space Complexity: O(n)

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