Confused about hasattr/getattr/namespaces

[Brian Roberts]

I'm confused about the use of hasattr/getattr, or possibly
namespaces. I know how to do this:

class UnderstandThis(object):
def do_foo(self): pass
def do_bar(self): pass
def doit(self, cmd):
funcname = 'do_' + cmd
if hasattr(self, funcname):
getattr(self, funcname)()
else:
print 'not found'

But if I try to do this with classes in a module (instead of
functions in a class):

class FooGenerator(object): ...
class BarGenerator(object): ...

def generate(cmd):
clsname = cmd + 'Generator'
if hasattr(???, clsname):
etc...

I don't know what to use for ??? instead of self. If I print
globals() inside generate() it shows the two classes, but using
it in the hasattr line doesn't work -- huh? I can make it work
by wrapping the generate function in a (otherwise useless) class
and using self -- again, huh?

Couldn't find an explanation or example in the docs. In fact,
the description of vars/globals/locals (in section 2.1) just
confused me even more. Think I'm heading down the wrong path.
Can somebody please un-confuse me?

Brian.

 

[Jeff Epler]

Here's one way:
def generate(cmd):
clsname = cmd + "Generator"
g = globals()
if g.has_key(clsname): ...
globals() returns the module's dict, not the module. You could also
import modulename as self
but this is a kind of circular import, and the re-use of the name "self"
(which will be used in method definitions) smells bad too.

Jeff

 

[Bob Ippolito]

I'm confused about the use of hasattr/getattr, or possibly
namespaces. I know how to do this:

class UnderstandThis(object):
def do_foo(self): pass
def do_bar(self): pass
def doit(self, cmd):
funcname = 'do_' + cmd
if hasattr(self, funcname):
getattr(self, funcname)()
else:
print 'not found'

But if I try to do this with classes in a module (instead of
functions in a class):

class FooGenerator(object): ...
class BarGenerator(object): ...

def generate(cmd):
clsname = cmd + 'Generator'
if hasattr(???, clsname):
etc...

I don't know what to use for ??? instead of self. If I print
globals() inside generate() it shows the two classes, but using
it in the hasattr line doesn't work -- huh? I can make it work
by wrapping the generate function in a (otherwise useless) class
and using self -- again, huh?

Couldn't find an explanation or example in the docs. In fact,
the description of vars/globals/locals (in section 2.1) just
confused me even more. Think I'm heading down the wrong path.
Can somebody please un-confuse me?

if you have the module object, you can use that.. or you could use
sys.modules[__name__] to get the current module (import sys, of course).

globals(), locals() are dictionaries, so you would have to do "clsobj =
globals().get(clsname)" or something like that. You *probably* want
something more explicit than that though.. it probably wouldn't be too
much work to keep your own command->class dictionary.

-bob