Code Sample, a copy-pastable example if possible

s = Series(["HCPSS_000_123", "HCPSS_100_1234", "HCPSS_200_1234"], index=["CM_1","CM_2","CM_3"]) module = s.str.extractall("HCPSS_(\d{3})")

Gives the following error

ValueError Traceback (most recent call last) in () ----> 1 module = s.str.extractall("HCPSS_(\d{3})")

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\core\strings.pyc in extractall(self, pat, flags) 1619 @copy(str_extractall) 1620 def extractall(self, pat, flags=0): -> 1621 return str_extractall(self._orig, pat, flags=flags) 1622 1623 _shared_docs['find'] = ("""

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\core\strings.pyc in str_extractall(arr, pat, flags) 711 if 0 < len(index_list): 712 index = MultiIndex.from_tuples( --> 713 index_list, names=arr.index.names + ["match"]) 714 else: 715 index = None

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in from_tuples(cls, tuples, sortorder, names) 893 arrays = lzip(*tuples) 894 --> 895 return MultiIndex.from_arrays(arrays, sortorder=sortorder, names=names) 896 897 @classmethod

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in from_arrays(cls, arrays, sortorder, names) 848 849 return MultiIndex(levels=levels, labels=labels, sortorder=sortorder, --> 850 names=names, verify_integrity=False) 851 852 @classmethod

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in new(cls, levels, labels, sortorder, names, copy, verify_integrity, _set_identity, name, **kwargs) 95 if names is not None: 96 # handles name validation ---> 97 result._set_names(names) 98 99 if sortorder is not None:

C:\Users\lmudge\AppData\Local\Continuum\Anaconda2\lib\site-packages\pandas\indexes\multi.pyc in _set_names(self, names, level, validate) 450 raise ValueError('Length of names must match length of level.') 451 if validate and level is None and len(names) != self.nlevels: --> 452 raise ValueError('Length of names must match number of levels in ' 453 'MultiIndex.') 454

ValueError: Length of names must match number of levels in MultiIndex.

Expected Output

No error

output of pd.show_versions()

INSTALLED VERSIONS

commit: None python: 2.7.12.final.0 python-bits: 64 OS: Windows OS-release: 7 machine: AMD64 processor: Intel64 Family 6 Model 78 Stepping 3, GenuineIntel byteorder: little LC_ALL: None LANG: None

pandas: 0.18.1 nose: 1.3.7 pip: 8.1.2 setuptools: 23.0.0 Cython: 0.24 numpy: 1.11.1 scipy: 0.17.1 statsmodels: 0.6.1 xarray: None IPython: 4.2.0 sphinx: 1.4.1 patsy: 0.4.1 dateutil: 2.5.3 pytz: 2016.4 blosc: None bottleneck: 1.1.0 tables: 3.2.2 numexpr: 2.6.0 matplotlib: 1.5.1 openpyxl: 2.3.2 xlrd: 1.0.0 xlwt: 1.1.2 xlsxwriter: 0.9.2 lxml: 3.6.0 bs4: 4.4.1 html5lib: None httplib2: None apiclient: None sqlalchemy: 1.0.13 pymysql: None psycopg2: None jinja2: 2.8 boto: 2.40.0 pandas_datareader: None

Comment From: jreback

Looks like solved in #13156 

In [9]: module
Out[9]: 
              0
     match     
CM_1 0      000
CM_2 0      100
CM_3 0      200

In [10]: s
Out[10]: 
CM_1     HCPSS_000_123
CM_2    HCPSS_100_1234
CM_3    HCPSS_200_1234
dtype: object

In [11]: pd.__version__
Out[11]: '0.19.0rc1+23.gdb9dc65'

Comment From: jorisvandenbossche

@lmudge BTW, I think in this case you rather want to use extract instead of extractall