以下は，前回の投稿で用いた query 関数の使い方を調べてみた結果です．
>>> help(sample_df.query)
Help on method query in module pandas.core.frame:
query(expr, inplace=False, **kwargs) method of pandas.core.frame.DataFrame instance
Query the columns of a DataFrame with a boolean expression.
Parameters
----------
expr : string
The query string to evaluate. You can refer to variables
in the environment by prefixing them with an '@' character like
``@a + b``.
inplace : bool
Whether the query should modify the data in place or return
a modified copy
.. versionadded:: 0.18.0
kwargs : dict
See the documentation for :func:`pandas.eval` for complete details
on the keyword arguments accepted by :meth:`DataFrame.query`.
Returns
-------
q : DataFrame
See Also
--------
pandas.eval
DataFrame.eval
Notes
-----
The result of the evaluation of this expression is first passed to
:attr:`DataFrame.loc` and if that fails because of a
multidimensional key (e.g., a DataFrame) then the result will be passed
to :meth:`DataFrame.__getitem__`.
This method uses the top-level :func:`pandas.eval` function to
evaluate the passed query.
The :meth:`~pandas.DataFrame.query` method uses a slightly
modified Python syntax by default. For example, the ``&`` and ``|``
(bitwise) operators have the precedence of their boolean cousins,
:keyword:`and` and :keyword:`or`. This *is* syntactically valid Python,
however the semantics are different.
You can change the semantics of the expression by passing the keyword
argument ``parser='python'``. This enforces the same semantics as
evaluation in Python space. Likewise, you can pass ``engine='python'``
to evaluate an expression using Python itself as a backend. This is not
recommended as it is inefficient compared to using ``numexpr`` as the
engine.
The :attr:`DataFrame.index` and
:attr:`DataFrame.columns` attributes of the
:class:`~pandas.DataFrame` instance are placed in the query namespace
by default, which allows you to treat both the index and columns of the
frame as a column in the frame.
The identifier ``index`` is used for the frame index; you can also
use the name of the index to identify it in a query. Please note that
Python keywords may not be used as identifiers.
For further details and examples see the ``query`` documentation in
:ref:`indexing <indexing.query>`.
Examples
--------
>>> df = pd.DataFrame(np.random.randn(10, 2), columns=list('ab'))
>>> df.query('a > b')
>>> df[df.a > df.b] # same result as the previous expression
~
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