float_format in to_latex can be a function

[toobaz]

The docs for to_latex(float_format=) say

float_format : str, optional
    Format string for floating point numbers.

and indeed the code contains a comment confirming this:

pandas/pandas/io/formats/format.py

Line 1010 in 8b48f5c

# float_format is expected to be a string

... but it does accept a function:

In [2]: s = pd.Series(1/3, index=range(3))                                                                                                                                                                                                    

In [3]: s.to_latex(float_format='{:0.2f}'.format)                                                                                                                                                                                             
Out[3]: '\\begin{tabular}{lr}\n\\toprule\n{} &    0 \\\\\n\\midrule\n0 & 0.33 \\\\\n1 & 0.33 \\\\\n2 & 0.33 \\\\\n\\bottomrule\n\\end{tabular}\n'

... and formatters (mentioned in the comment above) does not apply to Series (?), and is not as convenient for DataFrames (it requires to explicitly mention each column name).

So I guess we just want to document that it can be either a string, or a function.

Output of pd.show_versions()

INSTALLED VERSIONS

commit : f58a1fe
python : 3.7.3.candidate.1
python-bits : 64
OS : Linux
OS-release : 4.9.0-9-amd64
machine : x86_64
processor :
byteorder : little
LC_ALL : None
LANG : it_IT.UTF-8
LOCALE : it_IT.UTF-8

pandas : 0.25.0.dev0+854.gf58a1fee7.dirty
numpy : 1.16.4
pytz : 2016.7
dateutil : 2.8.0
pip : 9.0.1
setuptools : 41.0.1
Cython : 0.29.2
pytest : 4.6.3
hypothesis : 3.71.11
sphinx : 1.4.9
blosc : None
feather : None
xlsxwriter : 0.9.6
lxml.etree : 4.3.2
html5lib : 0.999999999
pymysql : None
psycopg2 : None
jinja2 : 2.10.1
IPython : 7.5.0
pandas_datareader: 0.2.1
bs4 : 4.5.3
bottleneck : 1.2.1
fastparquet : None
gcsfs : None
lxml.etree : 4.3.2
matplotlib : 3.0.2
numexpr : 2.6.9
openpyxl : 2.3.0
pandas_gbq : None
pyarrow : None
pytables : None
s3fs : None
scipy : 1.1.0
sqlalchemy : 1.0.15
tables : 3.4.4
xarray : None
xlrd : 1.0.0
xlwt : 1.3.0
xlsxwriter : 0.9.6

[toobaz]

One further reason to allow functions might be that strings only support the Python 2.x syntax. - although we would probably like to change this sooner or later.