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Python: removeprefix() and removesuffix()

Swastik Baranwal
A noob
Updated on ・1 min read

In Python 3.9 which is scheduled in to be released in October 2020
has introduced two new string methods str.removeprefix() and str.removesuffix() respectively.

Why

There were a lot of confusions as people thought str.lstrip() and str.rstrip() that it can be used to trim prefix and suffix but the parameter accepts a set of characters not the substring.

These methods are useful for trimming prefix/suffix and also make code short and readable.

Purpose

  • str.removeprefix(substring: string) is a method which returns a new string with the trimmed prefix if the str starts with it else it will return the original string.

  • str.removesuffix(substring: string) is a method which returns a new string with the trimmed suffix if the str ends with it else it will return the original string.

Implementation

These functions were implemented in python/cpython#18939.

  • removepreifx()
def removeprefix(self: str, prefix: str, /) -> str:
    if self.startswith(prefix):
        return self[len(prefix):]
    else:
        return self[:]
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  • removesuffix()
def removesuffix(self: str, suffix: str, /) -> str:
    if self.endswith(suffix):
        return self[:-len(suffix)]
    else:
        return self[:]
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Usage

This shows the usage of the functions and the output of all the cases.

s = 'Hello World from Python 3.9!'
print(s.removeprefix('Hello World')) // from Python 3.9!
print(s.removeprefix('')) // Hello World from Python 3.9!

print(s.removesuffix('3.9!')) // Hello World from Python
print(s.removesuffix('Python')) // Hello World from Python 3.9! 
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Conclusion

Python is always evolving with the community needs and it will be most used language in the future.

Discussion (2)

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jdoe profile image
John Doe • Edited

You said "In Python 3.9 which is scheduled in to be released in October 2021". Did you mean October 2020?

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delta456 profile image
Swastik Baranwal Author

I think I did a typo. My bad, I will update it, thanks!