Python classes: having instance method in one class point to instance method in another class

Question

I have a class (I will call it "master class") that uses instance methods from multiple other classes. The other classes are imported on __init__ and are stored as private instance attributes.

I would like to use the other class's instance methods, with the following properties:

Not rewrite docstrings or signature in the master class
Have autodoc parse the docstrings from the other classes as if they were docstrings for the master class

Currently, the way I have it set up:

class OtherClass:
    """Some other class that I import."""

    def __init__(self):
        pass

    def print_num(self, num: float = 15) -> None:
        """Print a num.

        Args:
            num: Number to print

        """
        print(num)

from .other import OtherClass


class MasterClass:

    def __init__(self, other_class: OtherClass):
        """Create master class with a bunch of other classes.

        For simplicity, I only included one class here as an arg.

        Args:
            other_class: Houses some methods

        """
        self._other_class = other_class

    def print_num(self, num: float = 15):
        """Print a num.

        Args:
            num: Number to print

        """
        self._other_class.print_num(num)

To pull in OtherClass.print_num, I had to:

Manually copy the signature
Manually copy the docstring (because I want my Sphinx documentation to be accurate)
Call OtherClass's method within MasterClass's method, passing in all the args and kwargs manually

Is there a better way to do this?

Thank you in advance for your guidance.

jferard · Accepted Answer · 2019-08-27 16:00:22Z

1

The function wraps from the module functools is what you need:

from functools import wraps

class OtherClass:
    def print_num(self, num: float=15) -> None:
        """Print a num.

        Args:
            num: Number to print

        """
        print(num)

class MasterClass:
    def __init__(self, other_class: OtherClass):
        self._other_class = other_class

    @wraps(OtherClass.print_num)
    def print_num(self, num=15):
        self._other_class.print_num(num)

print(MasterClass.print_num.__doc__)
print(MasterClass.print_num.__annotations__)

Output:

Print a num.

        Args:
            num: Number to print


{'num': <class 'float'>, 'return': None}

You still have to make the explicit call.

Note: your design is a special case of the facade pattern.

answered Aug 27, 2019 at 16:00

jferard

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1 Comment

Intrastellar Explorer Over a year ago

thank you so much for an informational answer, I was not previously aware of the facade pattern!

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