to_clipboard issue with float_format

[jorisvandenbossche]

Related to #9448, using the following example:

In [143]: df = pd.DataFrame(np.random.randn(5,2), columns=['A', 'B'])

In [144]: df
Out[144]:
          A         B
0 -1.151315 -2.174735
1 -1.031375 -1.957344
2 -0.619368 -0.835133
3  2.562381 -0.294245
4  2.432353  0.032805

to_clipboard is said to pass the kwargs to to_csv (see docs: http://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.to_clipboard.html). However, that seems not be fully true for the float_format kwarg:

df.to_clipboard(float_format='%.3f')
->
    A   B
0   -1.151  -2.175
1   -1.031  -1.957
2   -0.619  -0.835
3   2.562   -0.294
4   2.432   0.033

Now using a callable:

df.to_clipboard(float_format='{:.3f}'.format)
->
       A      B
0 -1.151 -2.175
1 -1.031 -1.957
2 -0.619 -0.835
3  2.562 -0.294
4  2.432  0.033

but this does not work with to_csv:

In [150]: df.to_csv(float_format='{:.3f}'.format)
---------------------------------------------------------------------------
TypeError: unsupported operand type(s) for %: 'builtin_function_or_method' and 'float'

Furthermore, when using a function as float_format, the result is no longer pastable in excel, even with excel=True (the default).

[jorisvandenbossche]

OK, looking at to_clipboard, this is of course just because when to_csv fails, it is passed on to to_string. However:

• this is not mentioned in the docs (and to_string has different parameters/defaults, so this has a impact)
• this defeats the purpose of excel=True

[jreback]

Yeah, I think we should NOT fallback here. Forgot exactly why were doing that in the first place. So mark this a bug/API then.