Document Using Regex for str.split

import pandas as pd
df = pd.DataFrame({'col': ['a-b-c+e=d,f#t']*5})
df.col.str.split('+|=', expand=True)

Problem description

While passing two patterns separating with | to str.split() method, if one of them is +, panads returns the following error:

---------------------------------------------------------------------------
error                                     Traceback (most recent call last)
 in 
      2 import pandas as pd
      3 df = pd.DataFrame({'col': ['a-b-c+e=d,f#t']*5})
----> 4 df.col.str.split('+|=', expand=True)

~\Anaconda3\lib\site-packages\pandas\core\strings.py in split(self, pat, n, expand)
   2328     @copy(str_split)
   2329     def split(self, pat=None, n=-1, expand=False):
-> 2330         result = str_split(self._data, pat, n=n)
   2331         return self._wrap_result(result, expand=expand)
   2332 

~\Anaconda3\lib\site-packages\pandas\core\strings.py in str_split(arr, pat, n)
   1458             if n is None or n == -1:
   1459                 n = 0
-> 1460             regex = re.compile(pat)
   1461             f = lambda x: regex.split(x, maxsplit=n)
   1462     res = _na_map(f, arr)

~\Anaconda3\lib\re.py in compile(pattern, flags)
    231 def compile(pattern, flags=0):
    232     "Compile a regular expression pattern, returning a pattern object."
--> 233     return _compile(pattern, flags)
    234 
    235 def purge():

~\Anaconda3\lib\re.py in _compile(pattern, flags)
    299     if not sre_compile.isstring(pattern):
    300         raise TypeError("first argument must be string or compiled pattern")
--> 301     p = sre_compile.compile(pattern, flags)
    302     if not (flags & DEBUG):
    303         if len(_cache) >= _MAXCACHE:

~\Anaconda3\lib\sre_compile.py in compile(p, flags)
    560     if isstring(p):
    561         pattern = p
--> 562         p = sre_parse.parse(p, flags)
    563     else:
    564         pattern = None

~\Anaconda3\lib\sre_parse.py in parse(str, flags, pattern)
    853 
    854     try:
--> 855         p = _parse_sub(source, pattern, flags & SRE_FLAG_VERBOSE, 0)
    856     except Verbose:
    857         # the VERBOSE flag was switched on inside the pattern.  to be

~\Anaconda3\lib\sre_parse.py in _parse_sub(source, state, verbose, nested)
    414     while True:
    415         itemsappend(_parse(source, state, verbose, nested + 1,
--> 416                            not nested and not items))
    417         if not sourcematch("|"):
    418             break

~\Anaconda3\lib\sre_parse.py in _parse(source, state, verbose, nested, first)
    614             if not item or (_len(item) == 1 and item[0][0] is AT):
    615                 raise source.error("nothing to repeat",
--> 616                                    source.tell() - here + len(this))
    617             if item[0][0] in _REPEATCODES:
    618                 raise source.error("multiple repeat",

error: nothing to repeat at position 0

INSTALLED VERSIONS

commit: None python: 3.6.8.final.0 python-bits: 64 OS: Windows OS-release: 10 machine: AMD64 processor: Intel64 Family 6 Model 142 Stepping 10, GenuineIntel byteorder: little LC_ALL: None LANG: None LOCALE: None.None

pandas: 0.23.4 pytest: 3.7.1 pip: 18.1 setuptools: 40.2.0 Cython: 0.29.2 numpy: 1.15.4 scipy: 1.2.0 pyarrow: None xarray: 0.11.0 IPython: 7.1.1 sphinx: 1.7.6 patsy: 0.5.1 dateutil: 2.7.3 pytz: 2018.5 blosc: None bottleneck: 1.2.1 tables: 3.4.3 numexpr: 2.6.9 feather: None matplotlib: 3.0.2 openpyxl: 2.5.5 xlrd: 1.1.0 xlwt: 1.3.0 xlsxwriter: 1.0.5 lxml: 4.2.4 bs4: 4.7.1 html5lib: 1.0.1 sqlalchemy: 1.2.10 pymysql: None psycopg2: 2.7.6.1 (dt dec pq3 ext lo64) jinja2: 2.10 s3fs: None fastparquet: None pandas_gbq: None pandas_datareader: None

[WillAyd]

It’s consistent with regex behavior where + is a special character. You will get the same error with * amongst others as well

[WillAyd]

@zangell44 I think it is documented in most methods but sure if you see others where it isn’t by all means include in a PR