str.strip() strange behavior

>>> t1 = "abcd.org.开发者_Go百科gz"
>>> t1
'abcd.org.gz'
>>> t1.strip("g")
'abcd.org.gz'
>>> t1.strip("gz")
'abcd.org.'
>>> t1.strip(".gz")
'abcd.or'

Why is the 'g' of '.org' gone?

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strip(".gz") removes any of the characters ., g and z from the beginning and end of the string.

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x.strip(y) will remove all characters that appear in y from the beginning and end of x.

That means

'foo42'.strip('1234567890') == 'foo'

becuase '4' and '2' both appear in '1234567890'.

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Use os.path.splitext if you want to remove the file extension.

>>> import os.path
>>> t1 = "abcd.org.gz"
>>> os.path.splitext(t1)
('abcd.org', '.gz')

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In Python 3.9, there are two new string methods .removeprefix() and .removesuffix() to remove the beginning or end of a string, respectively. Thankfully this time, the method names make it aptly clear what these methods are supposed to perform.

>>> print (sys.version)
3.9.0 
>>> t1 = "abcd.org.gz"
>>> t1.removesuffix('gz')
'abcd.org.'
>>> t1
'abcd.org.gz'
>>> t1.removesuffix('gz').removesuffix('.gz')
'abcd.org.'     # No unexpected effect from last removesuffix call
 

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The argument given to strip is a set of characters to be removed, not a substring. From the docs:

The chars argument is a string specifying the set of characters to be removed.

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as far as I know strip removes from the beginning or end of a string only. If you want to remove from the whole string use replace.