Python regex: splitting on pattern match that is an empty string

by

It is unfortunate that the split requires a non-zero-width match, but it hasn’t been to fixed yet, since quite a lot incorrect code depends on the current behaviour by using for example [something]*as the regex. Use of such patterns will now generate a FutureWarning and those that never can split anything, throw a ValueError from Python 3.5 onwards:

>>> re.split(r'(?<!foo)(?=bar)', 'foobarbarbazbar')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.6/re.py", line 212, in split
    return _compile(pattern, flags).split(string, maxsplit)
ValueError: split() requires a non-empty pattern match.

The idea is that after a certain period of warnings, the behaviour can be changed so that your regular expression would work again.

If you can’t use the regex module, you can write your own split function using re.finditer():

def megasplit(pattern, string):
    splits = list((m.start(), m.end()) for m in re.finditer(pattern, string))
    starts = [0] + [i[1] for i in splits]
    ends = [i[0] for i in splits] + [len(string)]
    return [string[start:end] for start, end in zip(starts, ends)]

print(megasplit(r'(?<!foo)(?=bar)', 'foobarbarbazbar'))
print(megasplit(r'o', 'foobarbarbazbar'))

If you are sure that the matches are zero-width only, you can use the starts of the splits for easier code:

import re

def zerowidthsplit(pattern, string):
    splits = list(m.start() for m in re.finditer(pattern, string))
    starts = [0] + splits
    ends = splits + [ len(string) ]
    return [string[start:end] for start, end in zip(starts, ends)]

print(zerowidthsplit(r'(?<!foo)(?=bar)', 'foobarbarbazbar'))

More Related Contents:

  1. Split string on whitespace in Python [duplicate]
  2. How would I get everything before a : in a string Python
  3. Splitting a math expression string into tokens in Python
  4. Removing contents within brackets in string [duplicate]
  5. Regex not matching all the paranthesis substrings [duplicate]
  6. How to understand regular expression with python?
  7. How to extract numbers from a string in Python?
  8. Split string every nth character?
  9. Split a string by a delimiter in python
  10. Fast punctuation removal with pandas
  11. Python regex – r prefix
  12. How to input a regex in string.replace?
  13. How can I do multiple substitutions using regex?
  14. Splitting a string into words and punctuation
  15. How to split strings into text and number?
  16. Reading a text file and splitting it into single words in python
  17. Product code looks like abcd2343, how to split by letters and numbers?
  18. Get last “column” after .str.split() operation on column in pandas DataFrame
  19. How to match any string from a list of strings in regular expressions in python?
  20. Extract a string between double quotes
  21. Split string based on regex
  22. Convert list of strings to dictionary
  23. Is there a way to split a string by every nth separator in Python?
  24. Replace a string located between
  25. Remove Sub String by using Python
  26. How to split a Python string on new line characters [duplicate]
  27. Split string at every position where an upper-case word starts
  28. FutureWarning: The default value of regex will change from True to False in a future version
  29. How to use str.contains() with multiple expressions in pandas dataframes
  30. Python split string in moving window

Leave a Comment