series.str.cat(series.str) is concatenating only the largest string

[kayush2O6]

Code Sample, a copy-pastable example if possible

import pandas as pd

arr = ["AbC", "de", "FGHI", "j", "kLLLm"]

ps = pd.Series(arr)
expect = ps.str.cat(others=ps.str)
print(expect)
Out[16]:
0           NaN
1           NaN
2           NaN
3           NaN
4    kLLLmkLLLm
dtype: object

Problem description

series.str.cat(series.str) is concatenating only the largest string in the series but it should concatenate all the strings element wise.

Expected Output

Out[18]:
0        AbCAbC
1          dede
2      FGHIFGHI
3            jj
4    kLLLmkLLLm
dtype: object

Output of pd.show_versions()

In [2]: pandas.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.7.3.final.0
python-bits: 64
OS: Linux
OS-release: 3.10.0-862.14.4.el7.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: None
LOCALE: en_US.UTF-8

pandas: 0.24.2
pytest: 5.1.2
pip: 19.2.3
setuptools: 41.2.0
Cython: 0.29.13
numpy: 1.17.1
scipy: None
pyarrow: 0.14.1
xarray: None
IPython: 7.8.0
sphinx: 2.2.0
patsy: None
dateutil: 2.8.0
pytz: 2019.2
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml.etree: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10.1
s3fs: 0.3.4
fastparquet: None
pandas_gbq: None
pandas_datareader: None
gcsfs: None

[TomAugspurger]

I'm not sure what's going on, but that's not my expected output. series.str is an accessor, not an array-like of strings. I would expect an exception to be raised here.

[boomsquared]

I'm very new to python and there might be some misunderstanding on my part.

I believed the problem happens when passing StringMethods into is_list_like results in true (code).

This happens because StringMethods implements the iterator protocol (StringMethod's iterator, is_list_like implementation)

[WillAyd]

For the OP you probably just want expect = ps.str.cat(others=ps). @boomsquared if you have an idea of why this doesn't raise and would like to submit a PR would certainly welcome one

[boomsquared]

@WillAyd Thanks! Will give it a go

[SaturnFromTitan]

take

[SaturnFromTitan]

Like suggested in the PR discussion, I will implement a DeprecationWarning for Series.str.__iter__

[SaturnFromTitan]

Fyi: A FutureWarning was added and Series.str.__iter__ will be removed in a few versions. Until then, the issue remains open though, so we don't close it.

[jreback]

@SaturnFromTitan this can still be addressed independently right?