How to get class function object in Python class?

Question

I want to do some preparatory actions (e.g. logging) before function is called.

For example,

class Test(object):
  def float(self, target):
    logging.info('Call float() function')
    return float(target)

  def int(self, target):
    logging.info('Call int() function')
    return int(target)

t = Test()
a = t.float('123')
b = t.int('123')

However, now I have about 20 functions need to do the same thing. Is there any way I can use 1 function to fit all of them? Something like,

class Test(object):
  def __getattr__(self, name):
    def wrapper(args):
      return func(args) # is there any built-in funciton can get function object?
    logging.info('Call %s() function' % name)
    return wrapper

Hampus Larsson · Accepted Answer · 2020-08-21 13:59:10Z

5

You can use a decorator, to print out the name of the method before continuing to call the method:

def namer(var):
    def wrapper(*args, **kwargs):
        print(f'Call {var.__name__}() method')
        return var(*args, **kwargs)
    return wrapper

class Test(object):
    @namer
    def float(self, target):
        return float(target)

    @namer
    def int(self, target):
        return int(target)

t = Test()
a = t.float('123')
b = t.int('123')
print(a, b)

Output:

Call float() method
Call int() method
123.0 123

answered Aug 21, 2020 at 13:59

Hampus Larsson

3,0982 gold badges17 silver badges22 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

LaoDa581 Over a year ago

Thanks for your advise. But is there any chance I can catch the function object and use it directly? Or I have to keep overwriting functions if 20 more functions are added in the future.

Marcel Wilson Over a year ago

@kolin I'm not I understand what you're asking. What do you mean by 'overwriting functions'?

Marcel Wilson · Accepted Answer · 2020-08-21 21:24:42Z

This will include the arguments used in the logging of the method.

from functools import wraps

def logit(function):
    @wraps(function)
    def traced_func(self, *args, **kwargs):
        sargs = list(args)
        sargs += ["{farg}={fval!r}".format(farg=farg, fval=fval) for farg, fval in kwargs.items()]
        print('Call {}({})'.format(function.__name__, ", ".join(map(str,sargs))))
        rt = function(self, *args, **kwargs)
        return rt
    return traced_func

class Something(object):
    @logit
    def float(self, target, arg=None):
        return float(target)
    
    @logit
    def int(self, target):
        return int(target)


t = Something()

x = t.float(4, arg=9)
z = t.float(5)
y = t.int(8)

output

Call float(4, arg=9)
Call float(5)
Call int(8)

Generally I would advise putting the decorator above each method, that's a bit more deliberate and readable. However, you did ask if there was a way to avoid doing that...

Use a decorator's decorator on the class.

# use the same decorator as the above example along with this
def decorate_methods(decorator):
    def traced_func(cls):
        for attr in cls.__dict__:
            if callable(getattr(cls, attr)):
                setattr(cls, attr, decorator(getattr(cls, attr)))
        return cls
    return traced_func

@decorate_methods(logit)
class Test(object):
    def float(self, target):
        return float(target)

    def int(self, target):
        return int(target)

Partha Mandal · Accepted Answer · 2020-08-21 21:55:30Z

0

This is what you would want (and you wouldn't need to add a decorator for every function):

class Test(object):
    def float(self, target):
        return float(target)

    def int(self, target):
        return int(target)

    def __getattribute__(self, name):
      attr = super().__getattribute__(name)
      print(f'Call {attr.__name__}() method')
      return attr

t = Test()
a = t.float('123')
b = t.int('123')
print(a, b)

Output:

Call float() method
Call int() method
123.0 123

edited Aug 21, 2020 at 21:55

answered Aug 21, 2020 at 14:47

Partha Mandal

1,45111 silver badges16 bronze badges

6 Comments

Marcel Wilson Over a year ago

The top code doesn't output for me what you have there. Call Test() method is printed.

Partha Mandal Over a year ago

you ran the exact code snippet I pasted there? Or is the code you running different?

Marcel Wilson Over a year ago

Copied it directly. Ran it in 3.7.

Partha Mandal Over a year ago

Oh! I tested it out in 3.8.2 originally. But, then I tested out on colab with 3.6.9 - there also it worked! Not sure why your 3.7 would mess it up! And it's giving you Test as attr!!

Marcel Wilson Over a year ago

I'm a bonehead. I ran this in the debugger of Pycharm instead of running it straight in the interpreter. The code works fine. Since this code is messing with __getattribute__ there isn't a clean way to differentiate the regular calls from the ones that the debugger is making.

|

Emile · Accepted Answer · 2020-08-21 13:54:57Z

-2

You could do func = eval(name). It's not very elegant, nor very secure, but might do the job for what you want.

answered Aug 21, 2020 at 13:54

Emile

2,9912 gold badges19 silver badges22 bronze badges

Collectives™ on Stack Overflow

How to get class function object in Python class?

4 Answers 4

2 Comments

Comments

6 Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

2 Comments

Comments

6 Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related