Python: removeprefix() and removesuffix()

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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!