Improve `DataFrame.query` docstring with local variable example

What happened: Prepare Dask distributed:

from dask.distributed import Client

client = Client(n_workers=16,
                threads_per_worker=1)

This works:

import pandas as pd

data = {'col_1': [3, 2, 1, 0], 'col_2': ['a', 'b', 'c', 'd']}
df = pd.DataFrame.from_dict(data)
pick = 'c'
df.query('col_2 == @pick')

This doesn’t work:

dd_temp = dd.from_pandas(df, npartitions=2)
dd_temp.query('col_2 == @pick')

Throws UndefinedVariableError(“local variable ‘pick’ is not defined”).

What you expected to happen: Dask version of DataFrame.query should work as in pandas.

Minimal Complete Verifiable Example: See above

Anything else we need to know?: No

Environment:

• Dask version: 2021.8.0
• Python version: 3.9.6
• Operating System: Linux (Manjaro)
• Install method (conda, pip, source): conda-forge

[umonaca]

I’ll look into it tomorrow.

[jsignell]

Ohh! That’s true https://docs.dask.org/en/latest/generated/dask.dataframe.DataFrame.query.html is very thin! I only realized that pattern was supported because I was looking around in the tests. Please feel free to open a pull request with an example of that pattern @umonaca!