Create my own method for DataFrames (python)

Question

So I wanted to create a module for my own projects and wanted to use methods. For example I wanted to do:

from mymodule import *
df = pd.DataFrame(np.random.randn(4,4))
df.mymethod()

Thing is it seems I can't use .myfunc() since I think I can only use methods for the classes I've created. A work around is making mymethod a function and making it use pandas.Dataframes as a variable:

myfunc(df)

I don't really want to do this, is there anyway to implement the first one?

Answer 1

Nice solution can be found in ffn package. What authors do:

from pandas.core.base import PandasObject
def your_fun(df):
    ...
PandasObject.your_fun = your_fun

After that your manual function "your_fun" becomes a method of pandas.DataFrame object and you can do something like

df.your_fun()

This method will be able to work with both DataFrame and Series objects

Answer 2

This topic is well documented as of Nov 2019: Extending pandas

Note that the most obvious technique - Ivan Mishalkin's monkey patching - was actually removed at some point in the official documentation... probably for good reason.

Monkey patching works fine for small projects, but there is a serious drawback for a large scale project: IDEs like Pycharm can't introspect the patched-in methods. So if one right clicks "Go to declaration", Pycharm simply says "cannot find declaration to go to". It gets old fast if you're an IDE junkie.

I confirmed that Pycharm CAN introspect both the "custom accessors" and "subclassing" methods discussed in the official documentation.