Using tuple efficiently with strip()

Question

Consider a basic tuple used with the built-in method str.startswith():

>>> t = 'x','y','z'
>>> s = 'x marks the spot'
>>> s.startswith( t )
True

It seems a loop is required when using a tuple with str.strip():

>>> for i in t: s.strip(i)
... 
' marks the spot'
'x marks the spot'
'x marks the spot'

This seems wasteful perhaps; is there a more efficient way to use tuple items with str.strip()? s.strip(t) seemed logical, however, no bueno.

Answer 1

Stripping a string is a very different usecase from testing if a string starts with a given text, so the methods differ materially in how they treat their input.

str.strip() takes one string, which is treated as a set of characters; the string will be stripped of each of those characters in the set; as long as the string starts of ends with a character that is a member of the set, that starting or ending character is removed, until start and end are free of any characters from the given set.

If you have a tuple join it into one string:

s.strip(''.join(t))

or pass it in as a string literal:

s.strip('xyz')

Note that this means something different from using str.strip() with each individual tuple element!

Compare:

>>> s = 'yxz_middle_zxy'
>>> for t in ('x', 'y', 'z'):
...     print(s.strip(t))
... 
yxz_middle_zxy
xz_middle_zx
yxz_middle_zxy
>>> print(s.strip('xyz'))
_middle_

Even if you chained the str.strip() calls with individual character, it would still not produce the same output because the str.strip() call:

>>> for t in ('x', 'y', 'z'):
...     s = s.strip(t)
... 
>>> print(s)
xz_middle_zx

because the string never started or ended in x or z when those character were stripped; x only ended up at the start and end because the y character was stripped in a next step.