Python split string without splitting escaped character

Question

Is there a way to split a string without splitting escaped character? For example, I have a string and want to split by \':\' and not by \'\\:\'

http\\://ww         


        

Answer 1

I really know this is an old question, but i needed recently an function like this and not found any that was compliant with my requirements.

Rules:

• Escape char only works when used with escape char or delimiter. Ex. if delimiter is / and escape are \ then (\a\b\c/abc bacame ['\a\b\c', 'abc']
• Multiple escapes chars will be escaped. (\\ became \)

So, for the record and if someone look anything like, here my function proposal:

def str_escape_split(str_to_escape, delimiter=',', escape='\\'):
    """Splits an string using delimiter and escape chars

    Args:
        str_to_escape ([type]): The text to be splitted
        delimiter (str, optional): Delimiter used. Defaults to ','.
        escape (str, optional): The escape char. Defaults to '\'.

    Yields:
        [type]: a list of string to be escaped
    """
    if len(delimiter) > 1 or len(escape) > 1:
        raise ValueError("Either delimiter or escape must be an one char value")
    token = ''
    escaped = False
    for c in str_to_escape:
        if c == escape:
            if escaped:
                token += escape
                escaped = False
            else:
                escaped = True
            continue
        if c == delimiter:
            if not escaped:
                yield token
                token = ''
            else:
                token += c
                escaped = False
        else:
            if escaped:
                token += escape
                escaped = False
            token += c
    yield token

For the sake of sanity, i'm make some tests:

# The structure is:
# 'string_be_split_escaped', [list_with_result_expected]
tests_slash_escape = [
    ('r/casa\\/teste/g', ['r', 'casa/teste', 'g']),
    ('r/\\/teste/g', ['r', '/teste', 'g']),
    ('r/(([0-9])\\s+-\\s+([0-9]))/\\g<2>\\g<3>/g',
     ['r', '(([0-9])\\s+-\\s+([0-9]))', '\\g<2>\\g<3>', 'g']),
    ('r/\\s+/ /g', ['r', '\\s+', ' ', 'g']),
    ('r/\\.$//g', ['r', '\\.$', '', 'g']),
    ('u///g', ['u', '', '', 'g']),
    ('s/(/[/g', ['s', '(', '[', 'g']),
    ('s/)/]/g', ['s', ')', ']', 'g']),
    ('r/(\\.)\\1+/\\1/g', ['r', '(\\.)\\1+', '\\1', 'g']),
    ('r/(?<=\\d) +(?=\\d)/./', ['r', '(?<=\\d) +(?=\\d)', '.', '']),
    ('r/\\\\/\\\\\\/teste/g', ['r', '\\', '\\/teste', 'g'])
]

tests_bar_escape = [
    ('r/||/|||/teste/g', ['r', '|', '|/teste', 'g'])
]

def test(test_array, escape):
    """From input data, test escape functions

    Args:
        test_array ([type]): [description]
        escape ([type]): [description]
    """
    for t in test_array:
        resg = str_escape_split(t[0], '/', escape)
        res = list(resg)
        if res == t[1]:
            print(f"Test {t[0]}: {res} - Pass!")
        else:
            print(f"Test {t[0]}: {t[1]} != {res} - Failed! ")


def test_all():
    test(tests_slash_escape, '\\')
    test(tests_bar_escape, '|')


if __name__ == "__main__":
    test_all()

Answer 2

As Ignacio says, yes, but not trivially in one go. The issue is that you need lookback to determine if you're at an escaped delimiter or not, and the basic string.split doesn't provide that functionality.

If this isn't inside a tight loop so performance isn't a significant issue, you can do it by first splitting on the escaped delimiters, then performing the split, and then merging. Ugly demo code follows:

# Bear in mind this is not rigorously tested!
def escaped_split(s, delim):
    # split by escaped, then by not-escaped
    escaped_delim = '\\'+delim
    sections = [p.split(delim) for p in s.split(escaped_delim)] 
    ret = []
    prev = None
    for parts in sections: # for each list of "real" splits
        if prev is None:
            if len(parts) > 1:
                # Add first item, unless it's also the last in its section
                ret.append(parts[0])
        else:
            # Add the previous last item joined to the first item
            ret.append(escaped_delim.join([prev, parts[0]]))
        for part in parts[1:-1]:
            # Add all the items in the middle
            ret.append(part)
        prev = parts[-1]
    return ret

s = r'http\://www.example.url:ftp\://www.example.url'
print (escaped_split(s, ':')) 
# >>> ['http\\://www.example.url', 'ftp\\://www.example.url']

Alternately, it might be easier to follow the logic if you just split the string by hand.

def escaped_split(s, delim):
    ret = []
    current = []
    itr = iter(s)
    for ch in itr:
        if ch == '\\':
            try:
                # skip the next character; it has been escaped!
                current.append('\\')
                current.append(next(itr))
            except StopIteration:
                pass
        elif ch == delim:
            # split! (add current to the list and reset it)
            ret.append(''.join(current))
            current = []
        else:
            current.append(ch)
    ret.append(''.join(current))
    return ret

Note that this second version behaves slightly differently when it encounters double-escapes followed by a delimiter: this function allows escaped escape characters, so that escaped_split(r'a\\:b', ':') returns ['a\\\\', 'b'], because the first \ escapes the second one, leaving the : to be interpreted as a real delimiter. So that's something to watch out for.

Answer 3

I have created this method, which is inspired by Henry Keiter's answer, but has the following advantages:

• Variable escape character and delimiter
• Do not remove the escape character if it is actually not escaping something

This is the code:

def _split_string(self, string: str, delimiter: str, escape: str) -> [str]:
    result = []
    current_element = []
    iterator = iter(string)
    for character in iterator:
        if character == self.release_indicator:
            try:
                next_character = next(iterator)
                if next_character != delimiter and next_character != escape:
                    # Do not copy the escape character if it is inteded to escape either the delimiter or the
                    # escape character itself. Copy the escape character if it is not in use to escape one of these
                    # characters.
                    current_element.append(escape)
                current_element.append(next_character)
            except StopIteration:
                current_element.append(escape)
        elif character == delimiter:
            # split! (add current to the list and reset it)
            result.append(''.join(current_element))
            current_element = []
        else:
            current_element.append(character)
    result.append(''.join(current_element))
    return result

This is test code indicating the behavior:

def test_split_string(self):
    # Verify normal behavior
    self.assertListEqual(['A', 'B'], list(self.sut._split_string('A+B', '+', '?')))

    # Verify that escape character escapes the delimiter
    self.assertListEqual(['A+B'], list(self.sut._split_string('A?+B', '+', '?')))

    # Verify that the escape character escapes the escape character
    self.assertListEqual(['A?', 'B'], list(self.sut._split_string('A??+B', '+', '?')))

    # Verify that the escape character is just copied if it doesn't escape the delimiter or escape character
    self.assertListEqual(['A?+B'], list(self.sut._split_string('A?+B', '\'', '?')))

Answer 4

I think a simple C like parsing would be much more simple and robust.

def escaped_split(str, ch):
    if len(ch) > 1:
        raise ValueError('Expected split character. Found string!')
    out = []
    part = ''
    escape = False
    for i in range(len(str)):
        if not escape and str[i] == ch:
            out.append(part)
            part = ''
        else:
            part += str[i]
            escape = not escape and str[i] == '\\'
    if len(part):
        out.append(part)
    return out