On 3/14/2011 8:49 PM, Yaşar Arabacı wrote:
As I try to implement things with getattr, I am getting a really
strange error. This is my file:
Various interspersed comments:
#!/usr/bin/env python
# -*- encoding:utf-8 -*-
class global_variables:
It is customary to start class names with an uppercase letter
"Holds class attributes, so that other classes can share them"
products = 0
best_bundle = []
class dispatcher:
def GetMethod(self,class_name,method_name):
It is customary to start method names with a lowercase letter
"""This method first finds a class if desired classexists.
Then, instansites it, and returns a reference to desired
method of
the instance it created.
"""
from sys import modules
It is customary to place import statements close to the top of the
program, not in any class or function.
module = modules[self.__module__]
if hasattr(module,class_name):
What are the module's attributes?
insert print dir(module) to see ALL the attributes.
print "#debug : hasattr is true"
cls = getattr(module,class_name)
else:
print "#debug : hasattr is false"
return None
"if we get a valid class, lets instantie it"
if cls:
a=cls()
else:
return None
return hasattr(a,method_name) and getattr(a,method_name) or None
def dispatch_command(self):
"""Gets command from user, finds appropriate Class/method to run
and then runs it. Beware of the fact that, to be able to
successfully
run the method, method should take exactly two arguments,
arg 1: instance of class which method resides (e.g. self)
arg 2: list of other needed variables
list of other variables can be used to get as many variables
as possible
"""
command = raw_input(">>>")
args = command.split(" ")
if len(args) < 2:
return None
method = self.GetMethod(args[0],args[1])
return method and method(args[2:]) or None
class calculate(global_variables):
def bundle(self,args):
print "your best bundle is -->"
a = dispatcher()
a.dispatch_command()
Alternative 1
- put all the user-callable class definitions inside a Container class
(or whatever name you want)
- then use getattr on the Container class
class Container:
class Calculate(global_variables):
def bundle(self,args):
print "your best bundle is -->"
Alternative 2 - use the following to create a dictionary of classes in
which you look up the desired class by name
import sys, inspect
thisModule = sys.modules[__name__]
classDict = dict((name.lower(), value) for name, value in
inspect.getmembers(thisModule, inspect.isclass))
...
cls = classDict[className]
Alternative 3
cls = getattr(module,class_name)
try:
if issubclass(cls, global_variables)
a=cls()
except TypeError:
pass
I wanted to see what happens when someone gives an nonexistent
function. But when I put a b, it gives me error, when I put c d it
doesn't. I don't have either a or c classes, but a somehow causes
problems :S This is what I did:
yasar@yasar-laptop:~/best_buy> ./main.py
>>>a b
#debug : hasattr is true
Traceback (most recent call last):
File "./main.py", line 57, in <module>
a.dispatch_command()
File "./main.py", line 44, in dispatch_command
method = self.GetMethod(args[0],args[1])
File "./main.py", line 25, in GetMethod
a=cls()
AttributeError: dispatcher instance has no __call__ method
The error tells you what a is. Isn't it obvious now? Remember to read
and understand such messages.
yasar@yasar-laptop:~/best_buy> ./main.py
>>>c d
#debug : hasattr is false
--
Bob Gailer
919-636-4239
Chapel Hill NC
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