Is loc[ ] a function in Pandas

问题

Normal syntax for calling a function is func() but I have noticed that loc[] in pandas is without parentheses and still treated as a function. Is loc [] really a function in pandas?

回答1:

Is loc[ ] a function in Pandas?

No. The simplest way to check is:

import pandas as pd
df = pd.DataFrame()
print(df.loc.__class__)

which prints

<class 'pandas.core.indexing._LocIndexer'>

this tells us that df.loc is an instance of a _LocIndexer class. The syntax loc[] derives from the fact that _LocIndexer defines __getitem__ and __setitem__*, which are the methods python calls whenever you use the square brackets syntax.

^{*Technically, it's its base class _LocationIndexer that defines those methods, I'm simplifying a bit here}

回答2:

Create a simple DataFrame df and look at the type of df.loc:

>>> type(df.loc)
pandas.core.indexing._LocIndexer

This means calling loc on a DataFrame returns an object of the type _LocIndexer, so .loc is not a function or method.

Look at what happens when we inspect the type of an actual function / method of a DataFrame:

>>> type(df.rename)
method

So what really happens here, is that you are accessing an attribute of your DataFrame called loc, which contains an object of type _LocIndexer, which itself implements the dunder methods __getitem__. This is a magic method that can be implemented by an object in order to define what happens when the object is indexed with the square bracket notation, just like a list or a dictionary.

回答3:

LOC[] is a property that allows Pandas to query data within a dataframe in a standard format. Basically you're providing the index of the data you want.

来源：https://stackoverflow.com/questions/66043313/is-loc-a-function-in-pandas

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python

pandas