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Explicit return in __init__

__init__ is a special Python method that is automatically called when memory is allocated for a new object. The sole purpose of __init__ is to initialize the values of instance members for the new object. Using __init__ to return a value implies that a program is using __init__ to do something other than initialize the object. This logic should be moved to another instance method and called by the program later, after initialization.

Anti-pattern

The __init__ method of the Rectangle class below attempts to return the area of the rectangle within the __init__ method. This violates the rule of only using __init__ to initialize instance members.

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height
        self.area = width * height
        # causes "Explicit return in __init__" error
        return self.area

Best practices

Remove the return statement from the __init__ method

Remove the return statement in the __init__ method that is returning a value.

class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height
        self.area = width * height
        # return statement removed from here

Move the program logic to another instance method

There is no reason why the Rectangle class MUST return the area immediately upon initialization. This program logic should be moved to a separate method of the Rectangle class. The program can call the method later, after the object has successfully initialized.

class Rectangle(object):
    def __init__(self, width, height):
        self.width = width
        self.height = height
        self._area = width * height

    @property
    # moved the logic for returning area to a separate method
    def area(self):
        return self._area

Note that the class must inherit from object now, since the property decorator only works for new style classes.

References