dynamic func. call

[Duncan Booth]

ajikoe at gmail.com wrote:

> Try this:
> 
> def myfunc():
>   print "helo"
> 
> s = "myfunc()"
> a = eval(s)
> 

No, please don't try that. Good uses for eval are *very* rare, and this 
isn't one of them.

Use the 'a = locals()[x]()' suggestion (or vars() instead of locals()), or 
even better put all the functions callable by this method into a class and 
use getattr() on an instance of the class.

A Pythonic way to do this sort of thing is to put all the functions that 
are callable indirectly into a class and give them names which contain a 
prefix to make it obvious that they are callable in this way and then add 
the prefix onto the string:

class C:
   def command_myfunc(self):
      return 42

   def default_command(self):
      raise NotImplementedError('Unknown command')

   def execute(self, s):
      return getattr(self, 'command_'+s, self.default_command)()

commands = C()
print commands.execute('myfunc')

That way you can be quickly tell which functions can be called indirectly 
and which can't; you can control what happens when no suitable function 
exists; and you can easily extend the functionality by subclassing your 
base class.