User defined method as variable or argument

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User defined method as variable or argument - AeranicusCascadia - Dec-12-2017

I'll try to communicate this as clearly as possible. I am still fairly new. Thanks in advance!

Here is my issue, in a nutshell:

I have created a custom class with methods and instantiated it successfully.
I have created a list containing these instances.

When I call the method explicitly by referencing objects in my list by index, everything works fine.

When I store the method in a variable and try to apply it the same way I get an error ("name 'describe' is not defined").

Ultimately, I am trying to pass this user created method as an argument of a function, but the result is the same error as above.

Below is the pseudocode, which I think is the best way to communicate my problem.
All help is appreciated. I will clarify as best as I can. Thanks for your patience, I am trying to digest quite a few concepts here.

# Create custom class

class MyClass:

def constructor():
statement
statement

def my_method():
statment
statement

# Create some instances of custom class

item1 = MyClass()
item2 = MyClass()
item3 = MyClass()

# Create a list containing the instances

my_list = [item1, item2, item2]

[# This works perfectly:

result = my_list[index].my_method()

# This does not work:
# (Error = name 'my_method' is not defined)

m = my_method()
result = my_list[index].m

# This throws the same error:

my_function(my_list, my_method)

# However, the following works exactly as desired (obviously I adjust the parameters in the function definition according to which approach I am trying):

my_function(my_list).my_method()

RE: User defined method as variable or argument - AeranicusCascadia - Dec-12-2017

Maybe I can express it more concisely:

I don't want to hard code which method (imported from another user made module) is called in my function. I want to be able to pass the object and method as arguments. The potential methods I am passing are already built into the objects.

Something like this:

Def the_function( object_arg, method_arg() ):
- - Do the thing.

And call it:

the_function( the_cheese, cut() )

'cut()' is already a method for 'the_cheese' object.

I have the sense that this is a very fundamental issue, perhaps related to scope, but I have not been able to figure it out or find answers online.

RE: User defined method as variable or argument - ODIS - Dec-12-2017

This is evaluating of the method. Not saving method into the variable!

m = my_method()

This is few examples how to store method or call it from string variable:

class MyClass:
    def my_method(self):
        print("My method has been called")


my_object = MyClass()

# call 1 - storing method to the variable and then calling it
my_method = my_object.my_method
my_method()

# call 2 - calling method with name in string variable
method_name = "my_method"
getattr(my_object, method_name)()

RE: User defined method as variable or argument - AeranicusCascadia - Dec-13-2017

Thank you. I am working with what you've shown me and trying to find a solution.

Here is a cleaner example with actual code that replicates the error I am having:

# The class
class MyClass:
	# constructor
	def __init__(self):
		self.name = "a class"
		self.text = "I am for testing stuff."
		
	# One method
	def describe(self):
		print(self.name)
		print(self.text)

# An instance of 'MyClass'
my_obj = MyClass()
my_obj.name = "My Object"
my_obj.text = "I am a sample object, of the 'MyClass' class"


# Define simple function that takes an object and method as arguments
def my_function(the_object, the_method):
	the_object.the_method()
	
	
# Call the function with args
my_function(my_obj, describe)

"""
NameError: name 'describe' is not defined
"""

RE: User defined method as variable or argument - ODIS - Dec-13-2017

You must fix the end of the script a little bit to get it work:

# Define simple function that takes an object and method as arguments
def my_function(the_object, the_method):
    getattr(the_object, the_method)()


# Call the function with args
my_function(my_obj, "describe")

You called my_function with the describe variable which hasn't been defined. And inside my_function you called the method also bad. You must get the object method with getattr(object, name_of_the_method) and then call it with () - so getattr(object, name_of_the_method)()

RE: User defined method as variable or argument - AeranicusCascadia - Dec-13-2017

Thank you very much! I understand much better, now.