top button
Flag Notify
    Connect to us
      Facebook Login
      Site Registration Why to Join

Facebook Login
Site Registration
Print Preview

class factory question using python

0 votes

I am extending a parser and need to create many classes that are all subclassed from the same object (defined in an external library). When my module is loaded I need all the classes to be created with a particular name but the behavior is all the same. Currently I have a bunch of lines like this:

 class Vspace(Base.Command): pass
 class Boldpath(Base.Command): pass

There are a bunch of lines like that. Is there a better way? Something like

 newclasses = ['Vspace', 'Boldpath', ... ]
 for name in newclasses:
 tmp = type(name, (Base.Command,) {})
 tmp.__name__ = name

Is there a more pythonic way?

posted Jun 26, 2013 by anonymous

Share this question
Facebook Share Button Twitter Share Button Google+ Share Button LinkedIn Share Button Multiple Social Share Button

1 Answer

0 votes

What is your objection against that approach?
By the way, I don't think you need

  tmp.__name__ = name
answer Jun 26, 2013 by anonymous
Similar Questions
0 votes

Sorry for the vague title. Probably best to just show you the code that explains it better.

This is a simplified example of what I want to do:

from random import choice

class Expr(object):
 Expr(expr, op, val) -> an expression object.

 def __init__(self, expr, op='', val=''):
 self.expr = expr # can be another instance of Expression.
 self.op = op
 self.val = val

 def __str__(self):
 return ("%s %s %s" % (self.expr, self.op, self.val)).strip()

 def expand(self):
 self = Expr(self, choice('+-*/'), choice('12345'))

Then I tried messing around with Expr.__new__() and Expr.__init__() but that didn't work.

The only way I've got it to work is by doing the expanding part outside of the object, by a method of some other class. But I want the Expr class to be responsible for itself. How can I do this and why doesn't the above work?

+2 votes

It is difficult to install numpy package for my PC Windows 7, 64-bit OS. In the end, I install Enthought Canopy, which is recommended on line because it does install numpy automatically. Now, I can test it with

import numpy

it succeeds. On, it shows some interesting code example snippet, such as Cookbook / ParticleFilter, Markov chain etc.

I don't know how I can access these code examples, because I don't know where Enthought Canopy installs these package.

Could you help me on using numpy examples?

0 votes

I'm trying to figure out (or find an example) of polymorphism whereby I pass a commandline argument (a string) which comports to a class (in java, you would say that it comports to a given interface but I don't know if there is such a thing in Python) then that class of that name, somehow gets instantiated from that string. This way, I can have similar classes, but have my program use various ones by simply changing the commandline argument.

Can anyone show me how this might be done in Python?

Useful Links with Similar Problem
Contact Us
+91 9880187415
#470/147, 3rd Floor, 5th Main,
HSR Layout Sector 7,
Bangalore - 560102,
Karnataka INDIA.