[Tutor] How to use a str object, to find the class in exact name?

[Yaşar Arabacı]

Thanks for excellent explanations. I almost got this working. I just 
have one more problem, that is:

When user enter incorrect number of arguments for a method, I naturally 
get a type error. I could probably fix that with try and catch, but that 
is not very explanatory to the user. Is there a way to get expected 
number of arguments to the method so that I can generate an error report?

You can find my codes as attachment. I have split them into two files. 
In order to run it, you should run cli.py like:

python cli.py

Thanks in advance,

Yaşar Arabacı

15-03-2011 05:39, bob gailer yazmış:
> 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 at 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 at yasar-laptop:~/best_buy> ./main.py
>> >>>c d
>> #debug : hasattr is false
>>
>
>

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