lstrip正在删除一个我不期望的字符

Question

The following code:

s = "www.wired.com"
print s
s = s.lstrip('www.')
print s

outputs:

www.wired.com
ired.com

Note the missing w on the second line. I'm not sure I understand the behavior. I would expect:

www.wired.com
wired.com

EDIT:

Following the first two answers, I now understand the behavior. My question is now: how do I strip the leading www. without touching the rest ?

Answer 1

The argument to string.lstrip is a list of characters:

>>> help(string.lstrip)
Help on function lstrip in module string:

lstrip(s, chars=None)
    lstrip(s [,chars]) -> string

    Return a copy of the string s with leading whitespace removed.
    If chars is given and not None, remove characters in chars instead.

>>>

It removes ALL occurrences of those leading characters.

print s.lstrip('w.')  # does the same!

[EDIT]:

If you wanted to strop the initial www. , but only if it started with that, you could use a regular expression or something like:

s = s[4:] if s.startswith('www.') else s

Answer 2

According to the documentation:

The chars argument is a string specifying the set of characters to be removed...The chars argument is not a prefix ; rather, all combinations of its values are stripped

You would achieve the same result by just saying:

'www.wired.com'.lstrip('w.')

If you wanted something more general, I would do something like this:

i = find(s, 'www.')
if i >= 0:
   s = s[0:i] + s[i+4:]

Answer 3

To remove the leading www.

>>> import re
>>> s = "www.wired.com"
>>> re.sub(r'^www\.', '', s)
'wired.com'