Adding code and methods to a class dynamically

[Peter Hansen]

Sarir Khamsi wrote:
> I have a class (Command) that derives from cmd.Cmd and I want to add
> methods to it dynamically. I've added a do_alias() method and it would
> be nice if I could turn an alias command into a real method of Command
> (that way the user could get help and name completion). The code would
> be generated dynamically from what gets passed to the do_alias()
> method. I've tried looking in the Python cookbook and have tried:
> 
> def funcToMethod(func, clas, method_name=None):
>    setattr(clas, method_name or func.__name__, func)
> 
> class Command(object, cmd.Cmd):
>    # ...
>    def do_f1(self, rest): print 'In Command.do_f1()'
>    def do_alias(self, rest):
>       rest.strip() # remove leading and trailing whitespace
>       pat = re.compile(r'^(\w+)\s+(\w+)$')
>       mo = pat.search(rest)
>       if mo:
>          newName = mo.group(1)
>          existingName = mo.group(2)
>          code = 'def do_' + newName + '(self, rest):\n'
>          code += '   self.do_' + existingName + '(rest)\n'
>          exec code
>          funcToMethod(getattr(newModule, 'do_' + existingName),
>                       self,
>                       'do_' + 'existingName')
>       else:
>          print 'Invalid alias command'
> 
> but this does not seem to work. 

If it's truly just an alias you want, then something like this should 
work better.  Replace everything in the if mo: section with this:

if mo:
     newName = mo.group(1)
     existingName = mo.group(2)
     existingMethod = getattr(self, 'do_' + existingName)
     setattr(self, 'do_' + newName, existingMethod)


-Peter