gistfile1.txt

Python 3.6.9 (default, Oct 17 2019, 06:49:31)
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pandas as pd
>>> import numpy as np
>>> df1 = pd.DataFrame({'A': pd.Series([1, 3, np.nan], dtype='Int64'), 'B': list('abc')})
>>> df1
     A  B
0    1  a
1    3  b
2  NaN  c
>>> df1.dtypes
A     Int64
B    object
dtype: object
>>> df2 = pd.DataFrame({'C': list('xz')})
>>> df1.join(df2)
     A  B    C
0    1  a    x
1    3  b    z
2  NaN  c  NaN
>>> df2.join(df1)
   C  A  B
0  x  1  a
1  z  3  b
>>> df1.loc[:, 'G'] = np.nan
>>> df1
     A  B   G
0    1  a NaN
1    3  b NaN
2  NaN  c NaN
>>> df1.join(df2)
     A  B   G    C
0    1  a NaN    x
1    3  b NaN    z
2  NaN  c NaN  NaN
>>> df2.join(df1)
   C  A  B   G
0  x  1  a NaN
1  z  3  b NaN
>>> df1.loc[:, 'G'] = df1.loc[:, 'G'].astype('Int64')
>>> df1.dtypes
A     Int64
B    object
G     Int64
dtype: object
>>> df1.join(df2)
     A  B    G    C
0    1  a  NaN    x
1    3  b  NaN    z
2  NaN  c  NaN  NaN
>>> df2.join(df1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.6/site-packages/pandas/core/frame.py", line 6824, in join
    rsuffix=rsuffix, sort=sort)
  File "/usr/local/lib/python3.6/site-packages/pandas/core/frame.py", line 6839, in _join_compat
    suffixes=(lsuffix, rsuffix), sort=sort)
  File "/usr/local/lib/python3.6/site-packages/pandas/core/reshape/merge.py", line 48, in merge
    return op.get_result()
  File "/usr/local/lib/python3.6/site-packages/pandas/core/reshape/merge.py", line 560, in get_result
    concat_axis=0, copy=self.copy)
  File "/usr/local/lib/python3.6/site-packages/pandas/core/internals/managers.py", line 2061, in concatenate_block_managers
    concatenate_join_units(join_units, concat_axis, copy=copy),
  File "/usr/local/lib/python3.6/site-packages/pandas/core/internals/concat.py", line 240, in concatenate_join_units
    for ju in join_units]
  File "/usr/local/lib/python3.6/site-packages/pandas/core/internals/concat.py", line 240, in <listcomp>
    for ju in join_units]
  File "/usr/local/lib/python3.6/site-packages/pandas/core/internals/concat.py", line 194, in get_reindexed_values
    missing_arr = np.empty(self.shape, dtype=empty_dtype)
TypeError: data type not understood
>>> df2
   C
0  x
1  z
>>> df3 = pd.DataFrame({'Z': list('lmn')})
>>> df2.join(df3)
   C  Z
0  x  l
1  z  m
>>> df1.join(df3)
     A  B    G  Z
0    1  a  NaN  l
1    3  b  NaN  m
2  NaN  c  NaN  n
>>> df3.join(df1)
   Z    A  B    G
0  l    1  a  NaN
1  m    3  b  NaN
2  n  NaN  c  NaN