Strange behaviour of the precision display option

[dexter2206]

Consider the following example:

import pandas as pd
s = pd.Series([840.0, 4200.0])
pd.set_option('precision', 0)
print(s)
pd.set_option('precision',2)
print(s)

The first print produces 84, 420, while the second one produces correctly 840.0 and 4200.0.

Problem description

If I understand docs correctly, the precision option should affect only the number of digits after the decimal point, not the digits before it.

Expected Output

First print shows 840 and 4200 (or 840.0, 4200.0).

Output of pd.show_versions()

INSTALLED VERSIONS

commit: None
python: 3.6.3.final.0
python-bits: 64
OS: Linux
OS-release: 4.14.8-300.fc27.x86_64
machine: x86_64
processor: x86_64
byteorder: little
LC_ALL: None
LANG: pl_PL.UTF-8
LOCALE: pl_PL.UTF-8

pandas: 0.22.0
pytest: 3.3.1
pip: 9.0.1
setuptools: 36.5.0
Cython: None
numpy: 1.14.2
scipy: 0.19.1
pyarrow: None
xarray: None
IPython: 6.2.1
sphinx: None
patsy: 0.4.1
dateutil: 2.7.0
pytz: 2018.3
blosc: None
bottleneck: None
tables: None
numexpr: None
feather: None
matplotlib: 2.1.2
openpyxl: 2.4.9
xlrd: 1.0.0
xlwt: None
xlsxwriter: 1.0.2
lxml: None
bs4: None
html5lib: 1.0.1
sqlalchemy: None
pymysql: None
psycopg2: None
jinja2: 2.10
s3fs: None
fastparquet: None
pandas_gbq: None
pandas_datareader: None

[WillAyd]

I think your bug is a result of the code in _trim_zeros linked below - care to take a look and try a PR?

pandas/pandas/io/formats/format.py

Line 1391 in 2d491c3

def _trim_zeros(str_floats, na_rep='NaN'):

[dexter2206]

@WillAyd sure, I'll look into it.