to_latex with float_format doesn't work like expected

Code Sample

import pandas as pd
df = pd.DataFrame([[0.19999]])
print(df.to_latex(float_format='%.3f'))
# returns:
# \begin{tabular}{lr}
# \toprule
# {} &   0 \\
# \midrule
# 0 & 0.2 \\
# \bottomrule
# \end{tabular}

Problem description

The float format doesn’t seem to be respected in the example above. In contrast:

'%.3f' % df.values[0][0]
# returns
# '0.200'

I would expect the number to be rendered as 0.200 instead of 0.2.

Issue #6052 is possibly related, but the problem description is different.

Expected Output

\begin{tabular}{lr}
\toprule
{} &   0 \\
\midrule
0 & 0.200 \\
\bottomrule
\end{tabular}

Output of pd.show_versions()

Using Anaconda Python 3.6.5 with recent pandas 0.23.1.

INSTALLED VERSIONS
------------------
commit: None
python: 3.6.5.final.0
python-bits: 64
OS: Linux
OS-release: 4.4.0-128-generic
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: en_US.UTF-8
LOCALE: en_US.UTF-8

pandas: 0.23.1
pytest: None
pip: 10.0.1
setuptools: 39.2.0
Cython: None
numpy: 1.14.5
scipy: None
pyarrow: None
xarray: None
IPython: 6.4.0
sphinx: None
patsy: None
dateutil: 2.7.3
pytz: 2018.4
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: None
openpyxl: None
xlrd: None
xlwt: None
xlsxwriter: None
lxml: None
bs4: None
html5lib: None
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: None
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

[tomneep]

I think the problem is that trailing zeros are being “trimmed” away. Presuming float_format should override this behaviour then a potential fix is 79b5acb5929333f0d0cd602b5ac206b29cc589a6. If that sounds like the right logic then I’ll open a PR (when time permits).

[WillAyd]

float_format accepts a string for the other to_... functions and it should here, so this is still a bug if anyone wants to work it