Dynamically import and create class instance

Question

With my python application, I have 40 modules (classes) which contain a parser for some text. In my function I only want to instanciate and use a particular module. These are all sorted in the database.

I am at the point now where I know my parser, and have both the python file name and class I want to import and create

However.... How do you actually do this in python?

eg;

file_name = 'lex_parser'
class_name = 'LexParser'

how can I do....

from {file_name} import {class_name}
Parser = {class_name}()

Follow what I mean?

yak · Accepted Answer · 2011-11-14 13:08:55Z

6

Try this:

file_name = 'lex_parser'
class_name = 'LexParser'

Parser = getattr(__import__(file_name), class_name)

Note that file_name must not contain .py.

This won't work if the module is within a package because __import__ would return the top level package. In that case you can do this:

import sys

file_name = 'parsers.lex_parser'
class_name = 'LexParser'

__import__(file_name)
Parser = getattr(sys.modules[file_name], class_name)

This will work in both cases and is recommeded by the __import__ function documentation.

In both examples Parser is a class which you have to instantiate as normally:

parser = Parser()

edited Nov 14, 2011 at 13:08

answered Nov 14, 2011 at 13:02

yak

9,1012 gold badges34 silver badges25 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Some programmer dude · Accepted Answer · 2011-11-14 10:14:52Z

3

How about something like this:

module = __import__('my_module')
if hasattr(module, 'ClassName'):
    ClassName = module.ClassName
    my_object = ClassName()

answered Nov 14, 2011 at 10:14

Some programmer dude

411k36 gold badges420 silver badges655 bronze badges

2 Comments

Wizzard Over a year ago

Looks promising, however I get, ClassName = module.ClassName AttributeError: 'module' object has no attribute 'ClassName'

Some programmer dude Over a year ago

@Wizzard The identifiers I wrote is just examples, and you might have to use getattr to get the classes.

Collectives™ on Stack Overflow

Dynamically import and create class instance

2 Answers 2

Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related