Python split string without splitting escaped character - python-2.7

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\://www.example.url:ftp\://www.example.url
The result should be the following:
['http\://www.example.url' , 'ftp\://www.example.url']

Answer 1

There is a much easier way using a regex with a negative lookbehind assertion:
re.split(r'(?<!\\):', str)

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

The edited version of Henry's answer with Python3 compatibility, tests and fix some issues:
def split_unescape(s, delim, escape='\\', unescape=True):
"""
>>> split_unescape('foo,bar', ',')
['foo', 'bar']
>>> split_unescape('foo$,bar', ',', '$')
['foo,bar']
>>> split_unescape('foo$$,bar', ',', '$', unescape=True)
['foo$', 'bar']
>>> split_unescape('foo$$,bar', ',', '$', unescape=False)
['foo$$', 'bar']
>>> split_unescape('foo$', ',', '$', unescape=True)
['foo$']
"""
ret = []
current = []
itr = iter(s)
for ch in itr:
if ch == escape:
try:
# skip the next character; it has been escaped!
if not unescape:
current.append(escape)
current.append(next(itr))
except StopIteration:
if unescape:
current.append(escape)
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

Answer 4

building on #user629923's suggestion, but being much simpler than other answers:
import re
DBL_ESC = "!double escape!"
s = r"Hello:World\:Goodbye\\:Cruel\\\:World"
map(lambda x: x.replace(DBL_ESC, r'\\'), re.split(r'(?<!\\):', s.replace(r'\\', DBL_ESC)))

Answer 5

Here is an efficient solution that handles double-escapes correctly, i.e. any subsequent delimiter is not escaped. It ignores an incorrect single-escape as the last character of the string.
It is very efficient because it iterates over the input string exactly once, manipulating indices instead of copying strings around. Instead of constructing a list, it returns a generator.
def split_esc(string, delimiter):
if len(delimiter) != 1:
raise ValueError('Invalid delimiter: ' + delimiter)
ln = len(string)
i = 0
j = 0
while j < ln:
if string[j] == '\\':
if j + 1 >= ln:
yield string[i:j]
return
j += 1
elif string[j] == delimiter:
yield string[i:j]
i = j + 1
j += 1
yield string[i:j]
To allow for delimiters longer than a single character, simply advance i and j by the length of the delimiter in the "elif" case. This assumes that a single escape character escapes the entire delimiter, rather than a single character.
Tested with Python 3.5.1.

Answer 6

There is no builtin function for that.
Here's an efficient, general and tested function, which even supports delimiters of any length:
def escape_split(s, delim):
i, res, buf = 0, [], ''
while True:
j, e = s.find(delim, i), 0
if j < 0: # end reached
return res + [buf + s[i:]] # add remainder
while j - e and s[j - e - 1] == '\\':
e += 1 # number of escapes
d = e // 2 # number of double escapes
if e != d * 2: # odd number of escapes
buf += s[i:j - d - 1] + s[j] # add the escaped char
i = j + 1 # and skip it
continue # add more to buf
res.append(buf + s[i:j - d])
i, buf = j + len(delim), '' # start after delim

Answer 7

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

Answer 8

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 9

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 10

Note that : doesn't appear to be a character that needs escaping.
The simplest way that I can think of to accomplish this is to split on the character, and then add it back in when it is escaped.
Sample code (In much need of some neatening.):
def splitNoEscapes(string, char):
sections = string.split(char)
sections = [i + (char if i[-1] == "\\" else "") for i in sections]
result = ["" for i in sections]
j = 0
for s in sections:
result[j] += s
j += (1 if s[-1] != char else 0)
return [i for i in result if i != ""]