BUG: pd.DataFrame.transform recursively loops in some cases

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Code Sample, a copy-pastable example

pd.DataFrame({"a":[None]}).transform({"a":int})

Problem description

Executing the above causes recursion depth limit exception. This is confusing and it is harder to pinpoint/debug than the expected exception.

Expected Output

Something akin to the output of int(None)

Output of pd.show_versions()

INSTALLED VERSIONS ------------------ commit : None python : 3.7.5.final.0 python-bits : 64 OS : Darwin OS-release : 18.6.0 machine : x86_64 processor : i386 byteorder : little LC_ALL : None LANG : None LOCALE : None.UTF-8

pandas : 1.0.3 numpy : 1.18.4 pytz : 2020.1 dateutil : 2.8.1 pip : 19.2.3 setuptools : 41.2.0 Cython : None pytest : 3.10.1 hypothesis : None sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : None IPython : None pandas_datareader: None bs4 : None bottleneck : None fastparquet : None gcsfs : None lxml.etree : None matplotlib : None numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pytables : None pytest : 3.10.1 pyxlsb : None s3fs : None scipy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None xlwt : None xlsxwriter : None numba : None

[pedrooa]

I’ve looked into the try / except you mentioned(within aggregate of frame.py), and the recurssion occurs because the except is not doing anything with the error:

try:
    result, how = self._aggregate(func, axis=axis, *args, **kwargs)
except TypeError:
    pass

I’ve managed to fix it raising an error printing what went wrong, as in the following code:

try:
    result, how = self._aggregate(func, axis=axis, *args, **kwargs)
except TypeError as err:
    exc = TypeError(
                    "DataFrame constructor called with "
                    f"incompatible data and dtype: {err}"
                )
    raise exc from err

I am now just making sure this fix doesn’t break anything else.

[dsaxton]

@pedrooa Looks like the problem is the the try / except within aggregate of frame.py, would be interesting to look into why that’s needed and if there’s a better way to handle things