static? + some stuff

[Eric Brunel]

Daniel Schüle wrote:
> Hi all
> 
> I have 2 questions
> 1)
> is there a way do declare static variables in a class?
> I coded this logic in global variable foo_cnt

You just did:
 > class foo:
 >     a = b = None
 >     c = 0
 >     my_id = 0

a, b, c and my_id *are* class attributes. They are actually inherited by 
instances of foo, but declaring them this way makes them class attributes. You 
should have done:

class foo:
   cnt = 0
   def __init__(self, c=0):
     foo.cnt += 1
     self.a = self.b = None
     self.c = c
     self.my_id = foo.cnt
(...)

Attributes do not need to be *declared* at the top of the class in Python as in 
C++ or Java: initializing them in the __init__ method is enough, and is probably 
the safest way to handle them.

> 2)
> is there a way to see the types of all data/function members of a class?
> dir(cls) returns a list of strings (of members) so it's logical that
> type(tmp.i) fails ...
> is it possible at all?

Use the getattr built-in function:

def print_type_of_all_attr_of_class(cls):
     tmp = cls()
     attr = dir(tmp)
     print attr
     for i in attr:
         print type(getattr(tmp, i))

print_type_of_all_attr_of_class(foo)

You can see here that cnt is actually declared as an attribute of the *class* 
foo, since you see it when you do a dir(cls), but not when you do a dir(tmp).

> thanks for your time
> 
> --
> Daniel

HTH
-- 
- Eric Brunel <eric dot brunel at pragmadev dot com> -
PragmaDev : Real Time Software Development Tools - http://www.pragmadev.com