Python: removeprefix() and removesuffix()

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

Why

There were a lot of confusion as people thought str.lstrip() and str.rstrip() that 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[:]

• removesuffix()

def removesuffix(self: str, suffix: str, /) -> str:
    if self.endswith(suffix):
        return self[:-len(suffix)]
    else:
        return self[:]

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! 

Conclusion

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