Why does str.lstrip strips an extra character?

Question

Python 2.6 (trunk:66714:66715M, Oct  1 2008, 18:36:04) 
[GCC 4.0.1 (Apple Computer, Inc. build 5370)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> path = "/Volumes/Users"
>>> path.lstrip('/Volume')
's/Users'
>>> path.lstrip('/Volumes')
'Users'
>>>

I am expecting output of path.lstrip('/Volumes') should be /Users

Answer 1

lstrip is character-based, it removes all characters from the left end that are in that string.

To verify this, try this:

"/Volumes/Users".lstrip("semuloV/")

Since / is part of the string, it is removed.

I suspect you need to use slicing instead:

if s.startsWith("/Volumes"):
    s = s[8:]

but hopefully someone with more intimate knowledge of the Python library might give you a better option.

Answer 2

The argument passed to lstrip is taken as a set of characters!

>>> '   spacious   '.lstrip()
'spacious   '
>>> 'www.example.com'.lstrip('cmowz.')
'example.com'

See also the documentation

You might want to use str.replace()

str.replace(old, new[, count])
# e.g.
'/Volumes/Home'.replace('/Volumes', '' ,1)

Return a copy of the string with all occurrences of substring old replaced by new. If the optional argument count is given, only the first count occurrences are replaced.

For paths, you may want to use os.path.split(). It returns a list of the paths elements.

>>> os.path.split('/home/user')
('/home', '/user')

To your problem:

>>> path = "/vol/volume"
>>> path.lstrip('/vol')
'ume'

The example above shows, how lstrip() works. It removes '/vol' starting form left. Then, is starts again... So, in your example, it fully removed '/Volumes' and started removing '/'. It only removed the '/' as there was no 'V' following this slash.

HTH

Answer 3

lstrip doc says:

Return a copy of the string S with leading whitespace removed.
If chars is given and not None, remove characters in chars instead.
If chars is unicode, S will be converted to unicode before stripping

So you are removing every character that is contained in the given string, including both 's' and '/' characters.

Answer 4

Strip is character-based. If you are trying to do path manipulation you should have a look at os.path

>>> os.path.split("/Volumes/Users")
('/Volumes', 'Users')

Answer 5

Here is a primitive version of lstrip (that I wrote) that might help clear things up for you:

def lstrip(s, chars):
    for i in range len(s):
        char = s[i]
        if not char in chars:
            return s[i:]
        else:
            return lstrip(s[i:], chars)

Thus, you can see that every occurrence of of a character in chars is is removed until a character that is not in chars is encountered. Once that happens, the deletion stops and the rest of the string is simply returned