Python Forum

How do I read a class file in order to discover the existence of a certain method ?

This is not Java, there are no class files. If you want the help of class Spam if file eggs.py, you can do this

>>> import eggs
>>> help(eggs.Spam)

You could also type in an ordinary terminal (outside of python)

Output:
pydoc eggs.Spam

Hello! Probably you mixed something up, as no such a thing as "a class file" exists in Python... Perhaps you're looking for something else?

(Nov-10-2019, 04:39 PM)Gribouillis Wrote: [ -> ]This is not Java, there are no class files. If you want the help of class Spam if file eggs.py, you can do this

 >>> import eggs >>> help(eggs.Spam) 

You could also type in an ordinary terminal (outside of python)

Output:
 pydoc eggs.Spam 

What I need to find out if it is possible to know is whether a method of a particular class exists?

JohnnyCoffee Wrote:What I need to find out if it is possible to know is whether a method of a particular class exists?

Try this for example

>>> class A:
...     def foo(self): pass
...     def bar(self): pass
... 
>>> help(A)

Output:
class A(builtins.object)
 |  Methods defined here:
 |  
 |  bar(self)
 |  
 |  foo(self)
 |  
 |  ----------------------------------------------------------------------
 |  Data descriptors defined here:
 |  
 |  __dict__
 |      dictionary for instance variables (if defined)
 |  
 |  __weakref__
 |      list of weak references to the object (if defined)

(Jan-19-2020, 04:45 PM)Gribouillis Wrote: [ -> ]

JohnnyCoffee Wrote:What I need to find out if it is possible to know is whether a method of a particular class exists?

Try this for example

 >>> class A: ... def foo(self): pass ... def bar(self): pass ... >>> help(A) 

Output:
 class A(builtins.object) | Methods defined here: | | bar(self) | | foo(self) | | ---------------------------------------------------------------------- | Data descriptors defined here: | | __dict__ | dictionary for instance variables (if defined) | | __weakref__ | list of weak references to the object (if defined) 

Okay, is there any way to access the class file and see if a certain method exists?

JohnnyCoffee Wrote:Okay, is there any way to access the class file and see if a certain method exists?

You can try

import inspect
f = inspect.getfile(A)
s = inspect.getsource(A)

that kind of things.

(Jan-22-2020, 05:41 PM)Gribouillis Wrote: [ -> ]

JohnnyCoffee Wrote:Okay, is there any way to access the class file and see if a certain method exists?

You can try

 import inspect f = inspect.getfile(A) s = inspect.getsource(A) 

that kind of things.

I set up the example below that returns me (True) if the 'a' method exists :

import inspect

class A:
    def a():
        pass

exist = A()
s = inspect.ismethod(exist.a)
print(s)

But simulating the access to a method there is no 'b' and it returns an error message: AttributeError: 'A' object has no attribute 'b'. Would have to return the boolean (False)

Python doesn't have macros, so the stuff in the parenthesis is evaluated prior to ismethod being invoked. A reasonable workaround would be to catch the AttributeError, and treat that as False.

Because inspect.ismethod() doesn't do what you are expecting. You could use something like

>>> from types import FunctionType
>>> class A:
...     def a(self):
...         pass
... 
>>> 
>>> def hasmethod(cls, attr):
...     return hasattr(A, attr) and isinstance(getattr(A, attr), FunctionType)
... 
>>> hasmethod(A, 'a')
True
>>> hasmethod(A, 'b')
False

Now it depends on what you call a method, you could also try

>>> def hasmethod(cls, attr):
...     return callable(getattr(A, attr, None))
...