strip remove '_' unexpectedly

Question

>>> x = 'abc_cde_fgh'
>>> x.strip('abc_cde')
'fgh'

_fgh is expected.

How to understard this result?

Answer 1

Strip removes any characters it finds from either end from the substring: it doesn't remove a trailing or leading word.

This example demonstrates it nicely:

x.strip('ab_ch')
'de_fg'

Since the characters "a", "b", "c", "h", and "_" are in the remove case, the leading "abc_c" are all removed. The other characters are not removed.

If you would like to remove a leading or trailing word, I would recommend using re or startswith/endswith.

def rstrip_word(str, word):
    if str.endswith(word):
        return str[:-len(word)]
    return str

def lstrip_word(str, word):
    if str.startswith(word):
        return str[len(word):]
    return str

def strip_word(str, word):
    return rstrip_word(lstrip_word(str, word), word)

Removing Multiple Words

A very simple implementation (a greedy one) to remove multiple words from a string can be done as follows:

def rstrip_word(str, *words):
    for word in words:
        if str.endswith(word):
            return str[:-len(word)]
    return str

def lstrip_word(str, *words):
    for word in words:
        if str.startswith(word):
            return str[len(word):]
    return str

def strip_word(str, *words):
    return rstrip_word(lstrip_word(str, *words), *words)

Please note this algorithm is greedy, it will find the first possible example and then return: it may not behave as you expect. Finding the maximum length match (although not too tricky) is a bit more involved.

>>> strip_word(x, "abc", "adc_")
'_cde_fgh'