BUG: ExtensionArrays whose elements are non-numeric numpy arrays crash Series.__repr__()

[frreiss]

• I have checked that this issue has not already been reported.

• I have confirmed this bug exists on the latest version of pandas.

• (optional) I have confirmed this bug exists on the master branch of pandas.

---

Code Sample, a copy-pastable example

Prerequisites:

$ pip install pandas numpy memoized-property
$ pip install git+https://github.com/frreiss/text-extensions-for-pandas

Reproduce the problem, using TensorArray, our extension type for storing tensors in a Pandas series:

>>> import pandas as pd
>>> import numpy as np
>>> import text_extensions_for_pandas as tp
>>> # Integers work
    int_tensors = np.array([[1, 2], [3, 4]])
    int_tensor_series = pd.Series(tp.TensorArray(int_tensors))
    int_tensor_series

0   [1 2]
1   [3 4]
dtype: TensorType

>>> # Boolean values don't work
    bool_tensors = np.array([[True, False], [False, True]])
    bool_tensor_series = pd.Series(tp.TensorArray(bool_tensors))
    bool_tensor_series
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
~/pd/covid-notebooks/env/lib/python3.7/site-packages/IPython/core/formatters.py in __call__(self, obj)
    700                 type_pprinters=self.type_printers,
    701                 deferred_pprinters=self.deferred_printers)
--> 702             printer.pretty(obj)
    703             printer.flush()
    704             return stream.getvalue()

[...many lines of stack trace...]

~/pd/covid-notebooks/env/lib/python3.7/site-packages/pandas/io/formats/format.py in _format_strings(self)
   1255         fmt_values = []
   1256         for i, v in enumerate(vals):
-> 1257             if not is_float_type[i] and leading_space:
   1258                 fmt_values.append(" {v}".format(v=_format(v)))
   1259             elif is_float_type[i]:

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

Problem description

Series.__repr__() invokes ExtensionArrayFormatter to render extension types. If the individual elements managed by an ExtensionArray are numpy arrays (or slices of a larger numpy array), then ExtensionArrayFormatter uses Pandas' facilities for rendering numpy arrays. These facilities comprise the base class GenericArrayFormatter and subclasses such as FloatArrayFormatter for handling specific types (see pandas/io/formats/format.py). The formatters for numeric types can render numpy arrays with more than one dimension, but the base class GenericArrayFormatter cannot. The limitation appears to be an oversight. I will submit a small pull request with a fix in a few minutes.

Expected Output

The above code should output something like this:

0   [True False]
1   [False True]
dtype: TensorType

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.7.7.final.0
python-bits : 64
OS : Darwin
OS-release : 19.4.0
machine : x86_64
processor : i386
byteorder : little
LC_ALL : None
LANG : en_US.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.0.3
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 46.1.3.post20200330
Cython : 0.29.15
pytest : None
hypothesis : None
sphinx : None
blosc : None
feather : None
xlsxwriter : None
lxml.etree : None
html5lib : None
pymysql : None
psycopg2 : None
jinja2 : 2.11.1
IPython : 7.13.0
pandas_datareader: None
bs4 : None
bottleneck : None
fastparquet : 0.3.3
gcsfs : None
lxml.etree : None
matplotlib : 3.1.3
numexpr : None
odfpy : None
openpyxl : None
pandas_gbq : None
pyarrow : 0.13.0
pytables : None
pytest : None
pyxlsb : None
s3fs : None
scipy : 1.4.1
sqlalchemy : None
tables : None
tabulate : 0.8.3
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None
numba : 0.49.0