passing a function reference in python

Question

Ok, So I am seeing something weird and I think I misunderstood how to pass functions around in python..

class Foo:
  def execute(self, **kwargs):
    print "self is ", self # <foo.Foo object at 0x1012948d0>
    features = {func_name: feature_func(kwargs, arg=arg)for func_name, 
                              feature_func in Foo.ALGORITHMS.items()}

  def func1(self, **kwargs):
     print "self is " , self # prints {}
     self._funchelp()

  def __funchelp(self):
     # pass


  ALGORITHMS = {'func1': func1}

So, what I am not getting is why is self printing to be an empty dictionary??

features = {func_name: feature_func(kwargs, arg=arg)for func_name, 
                              feature_func in Foo.ALGORITHMS.items()}

Something gets messed up above

And then

self._funchelp() Returns AttributeError: 'dict' object has no attribute '_Foo__funchelp'

David Sanders · Accepted Answer · 2014-10-16 00:15:15Z

1

It's probably because you need to include self as the first argument to feature_func in your dict comprehension. Also, you need to put the ** in front of kwargs. You may also need to set the 'arg' key on kwargs as follows to avoid some kind of argument error. Not sure about that though:

kwargs['arg'] = 123
features = {func_name: feature_func(self, **kwargs) for func_name, 
                          feature_func in Foo.ALGORITHMS.items()}

The weird error is probably because you're trying to access _funchelp as an attribute on an empty dict object. Furthermore, your function is defined as __funchelp with two underscores, which could get mangled by python because of the way it handles double underscore attributes internally. I think _funchelp must be a typo because I don't think it would be mangling the name if that was really what was in your code.

edited Oct 16, 2014 at 0:15

answered Oct 15, 2014 at 23:57

David Sanders

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1 Comment

mjallday Over a year ago

this is correct, you're not instantiating an instance of the class. either make classmethods or instantiate an instance.

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