round method throws error if DataFrame includes Int64Dtype

[shouyu]

Code Sample, a copy-pastable example if possible

>>> import pandas as pd
>>> s = pd.Series([1, 2, None], dtype="Int64")
>>> s.round(1)
AttributeError: 'float' object has no attribute 'rint'

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.8/site-packages/pandas/core/series.py", line 2146, in round
    result = com.values_from_object(self).round(decimals)
TypeError: loop of ufunc does not support argument 0 of type float which has no callable rint method

Problem description

round method throws above error.
Expected behavior is same to int64 dtype and ignore NaN.

>>> s = pd.Series([1, 2], dtype="int64")
>>> s.round(1)
0    1
1    2
dtype: int64

Expected Output

>>> s = pd.Series([1, 2, None], dtype="Int64")
>>> s.round(1)
>>> s
0       1
1       2
2    <NA>
dtype: Int64

Output of pd.show_versions()

INSTALLED VERSIONS

commit : None
python : 3.8.1.final.0
python-bits : 64
OS : Linux
OS-release : 5.4.13-arch1-1
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : C.UTF-8
LOCALE : en_US.UTF-8

pandas : 1.0.0
numpy : 1.18.1
pytz : 2019.3
dateutil : 2.8.1
pip : 20.0.2
setuptools : 45.1.0
Cython : None
pytest : None
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 : None
pyxlsb : None
s3fs : None
scipy : None
sqlalchemy : None
tables : None
tabulate : None
xarray : None
xlrd : None
xlwt : None
xlsxwriter : None
numba : None

[TomAugspurger]

Do you know if np.round is a ufunc? If so, we could use that, since that will call np.round(s.array) and wrap it correctly.

However, we have

In [23]: np.round(s.array)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
AttributeError: 'int' object has no attribute 'rint'

The above exception was the direct cause of the following exception:

TypeError                                 Traceback (most recent call last)
<ipython-input-23-841bf54cafae> in <module>
----> 1 np.round(s.array)

<__array_function__ internals> in round_(*args, **kwargs)

~/Envs/pandas-dev/lib/python3.7/site-packages/numpy/core/fromnumeric.py in round_(a, decimals, out)
   3599     around : equivalent function; see for details.
   3600     """
-> 3601     return around(a, decimals=decimals, out=out)
   3602
   3603

<__array_function__ internals> in around(*args, **kwargs)

~/Envs/pandas-dev/lib/python3.7/site-packages/numpy/core/fromnumeric.py in around(a, decimals, out)
   3224
   3225     """
-> 3226     return _wrapfunc(a, 'round', decimals=decimals, out=out)
   3227
   3228

~/Envs/pandas-dev/lib/python3.7/site-packages/numpy/core/fromnumeric.py in _wrapfunc(obj, method, *args, **kwds)
     53     bound = getattr(obj, method, None)
     54     if bound is None:
---> 55         return _wrapit(obj, method, *args, **kwds)
     56
     57     try:

~/Envs/pandas-dev/lib/python3.7/site-packages/numpy/core/fromnumeric.py in _wrapit(obj, method, *args, **kwds)
     42     except AttributeError:
     43         wrap = None
---> 44     result = getattr(asarray(obj), method)(*args, **kwds)
     45     if wrap:
     46         if not isinstance(result, mu.ndarray):

TypeError: loop of ufunc does not support argument 0 of type int which has no callable rint method

numpy/numpy#13877 looks somewhat relevant...

[jbrockmendel]

Do you know if np.round is a ufunc?

Looks like it isnt.

>>> np.round
<function round_ at 0x11c1eee60>

[TomAugspurger]

@MarcoGorelli this is also failing on 0.25.3, so I don't think it's appropriate to target for 1.0.1

---

I think our choices here are to either

1. Add an ExtensionArray.round method
2. Implement __array_function__ on some of our EAs.

[MarcoGorelli]

Sorry, I have no recollection of having modified the milestone, I must have clicked by accident, will be careful to not do this again

[mzeitlin11]

Fixed with tests in #38844