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?

Answer 1

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()