Python dynamically add decorator to class' methods by decorating class

Question

say I have a class:

class x:

    def first_x_method(self):
        print \'doing first_x_method stuff...\'

    def second_x_method(self):
        print \'d         


        

Answer 1

Here's a version of the trace decorator implemented as a class which allows for the other use case asked for: passing in the function to decorate all member functions of the decorated class with.

import inspect


def log(func):
    def wrapped(*args, **kwargs):
        try:
            print "Entering: [%s] with parameters %s" % (func.__name__, args)
            try:
                return func(*args, **kwargs)
            except Exception, e:
                print 'Exception in %s : %s' % (func.__name__, e)
        finally:
            print "Exiting: [%s]" % func.__name__
    return wrapped


class trace(object):

    def __init__(self, f):
        self.f = f

    def __call__(self, cls):
        for name, m in inspect.getmembers(cls, inspect.ismethod):
            setattr(cls, name, self.f(m))
        return cls


@trace(log)
class X(object):

    def first_x_method(self):
        print 'doing first_x_method stuff...'

    def second_x_method(self):
        print 'doing second_x_method stuff...'

x = X()
x.first_x_method()
x.second_x_method()

Answer 2

Unless there is a definite reason to use a class as a decorator, I think it is usually easier to use functions to define decorators.

Here is one way to create a class decorator trace, which decorates all methods of a class with the log decorator:

import inspect


def log(func):
    def wrapped(*args, **kwargs):
        try:
            print("Entering: [%s] with parameters %s" % (func.__name__, args))
            try:
                return func(*args, **kwargs)
            except Exception as e:
                print('Exception in %s : %s' % (func.__name__, e))
        finally:
            print("Exiting: [%s]" % func.__name__)
    return wrapped


def trace(cls):
    # https://stackoverflow.com/a/17019983/190597 (jamylak)
    for name, m in inspect.getmembers(cls, lambda x: inspect.isfunction(x) or inspect.ismethod(x)):
        setattr(cls, name, log(m))

    return cls


@trace
class X(object):
    def first_x_method(self):
        print('doing first_x_method stuff...')

    def second_x_method(self):
        print('doing second_x_method stuff...')


x = X()
x.first_x_method()
x.second_x_method()

yields:

Entering: [first_x_method] with parameters (<__main__.X object at 0x7f19e6ae2e80>,)
doing first_x_method stuff...
Exiting: [first_x_method]
Entering: [second_x_method] with parameters (<__main__.X object at 0x7f19e6ae2e80>,)
doing second_x_method stuff...
Exiting: [second_x_method]