find_recursionlimit.py

• Current:

  iftest_func_name.startswith("test_"):print(test_func_name[5:])else:print(test_func_name)

• Improved:

  print(test_func_name.removeprefix("test_"))

deccheck.py

This is an interesting case because the author chose to use thestr.replace method in a situation where only a prefix wasintended to be removed.

• Current:

  iffuncname.startswith("context."):self.funcname=funcname.replace("context.","")self.contextfunc=Trueelse:self.funcname=funcnameself.contextfunc=False

• Improved:

  iffuncname.startswith("context."):self.funcname=funcname.removeprefix("context.")self.contextfunc=Trueelse:self.funcname=funcnameself.contextfunc=False

• Arguably further improved:

  self.contextfunc=funcname.startswith("context.")self.funcname=funcname.removeprefix("context.")

cookiejar.py

• Current:

  defstrip_quotes(text):iftext.startswith('"'):text=text[1:]iftext.endswith('"'):text=text[:-1]returntext

• Improved:

  defstrip_quotes(text):returntext.removeprefix('"').removesuffix('"')

test_i18n.py

• Current:

  creationDate=header['POT-Creation-Date']# peel off the escaped newline at the end of stringifcreationDate.endswith('\\n'):creationDate=creationDate[:-len('\\n')]

• Improved:

  creationDate=header['POT-Creation-Date'].removesuffix('\\n')

There were many other such examples in the stdlib.

Expand the lstrip and rstrip APIs

Becauselstrip takes a string as its argument, it could be viewedas taking an iterable of length-1 strings. The API could, therefore, begeneralized to accept any iterable of strings, which would besuccessively removed as prefixes. While this behavior would beconsistent, it would not be obvious for users to have to call'foobar'.lstrip(('foo',)) for the common use case of asingle prefix.

Remove multiple copies of a prefix

This is the behavior that would be consistent with the aforementionedexpansion of thelstrip/rstrip API – repeatedly applying thefunction until the argument is unchanged. This behavior is attainablefrom the proposed behavior via by the following:

>>>s='Foo'*100+'Bar'>>>prefix='Foo'>>>whiles.startswith(prefix):s=s.removeprefix(prefix)>>>s'Bar'

Raising an exception when not found

There was a suggestion thats.removeprefix(pre) should raise anexception ifnots.startswith(pre). However, this does not matchwith the behavior and feel of other string methods. There could berequired=False keyword added, but this violates the KISSprinciple.

Accepting a tuple of affixes

It could be convenient to write thetest_concurrent_futures.pyexample above asname.removesuffix(('Mixin','Tests','Test')), sothere was a suggestion that the new methods be able to take a tuple ofstrings as an argument, similar to thestartswith() API. Withinthe tuple, only the first matching affix would be removed. This wasrejected on the following grounds:

• This behavior can be surprising or visually confusing, especiallywhen one prefix is empty or is a substring of another prefix, as in'FooBar'.removeprefix(('','Foo'))=='FooBar'or'FooBartext'.removeprefix(('Foo','FooBar'))=='Bartext'.
• The API forstr.replace() only accepts a single pair ofreplacement strings, but has stood the test of time by refusing thetemptation to guess in the face of ambiguous multiple replacements.
• There may be a compelling use case for such a feature in the future,but generalization before the basic feature sees real-world use wouldbe easy to get permanently wrong.

Alternative Method Names

Several alternatives method names have been proposed. Some are listedbelow, along with commentary for why they should be rejected in favorofremoveprefix (the same arguments hold forremovesuffix).

• ltrim,trimprefix, etc.:

  “Trim” does in other languages (e.g. JavaScript, Java, Go, PHP)whatstrip methods do in Python.

• lstrip(string=...)

  This would avoid adding a new method, but for differentbehavior, it’s better to have two different methods than onemethod with a keyword argument that selects the behavior.

• remove_prefix:

  All of the other methods of the string API, e.g.str.startswith(), uselowercase rather thanlower_case_with_underscores.

• removeleft,leftremove, orlremove:

  The explicitness of “prefix” is preferred.

• cutprefix,deleteprefix,withoutprefix,dropprefix, etc.:

  Many of these might have been acceptable, but “remove” isunambiguous and matches how one would describe the “remove the prefix”behavior in English.

• stripprefix:

  Users may benefit from remembering that “strip” means workingwith sets of characters, while other methods work withsubstrings, so re-using “strip” here should be avoided.