get importlib Does python have an equivalent to Java Class.forName()?




3 Answers

Assuming the class is in your scope:

globals()['classname'](args, to, constructor)

Otherwise:

getattr(someModule, 'classname')(args, to, constructor)

Edit: Note, you can't give a name like 'foo.bar' to getattr. You'll need to split it by . and call getattr() on each piece left-to-right. This will handle that:

module, rest = 'foo.bar.baz'.split('.', 1)
fooBar = reduce(lambda a, b: getattr(a, b), rest.split('.'), globals()[module])
someVar = fooBar(args, to, constructor)
get class instance from string python

I have the need to take a string argument and create an object of the class named in that string in Python. In Java, I would use Class.forName().newInstance(). Is there an equivalent in Python?


Thanks for the responses. To answer those who want to know what I'm doing: I want to use a command line argument as the class name, and instantiate it. I'm actually programming in Jython and instantiating Java classes, hence the Java-ness of the question. getattr() works great. Thanks much.




Yet another implementation.

def import_class(class_string):
    """Returns class object specified by a string.

    Args:
        class_string: The string representing a class.

    Raises:
        ValueError if module part of the class is not specified.
    """
    module_name, _, class_name = class_string.rpartition('.')
    if module_name == '':
        raise ValueError('Class name must contain module part.')
    return getattr(
        __import__(module_name, globals(), locals(), [class_name], -1),
        class_name)



This is found in the python standard library, as unittest.TestLoader.loadTestsFromName. Unfortunately the method goes on to do additional test-related activities, but this first ha looks re-usable. I've edited it to remove the test-related functionality:

def get_object(name):
    """Retrieve a python object, given its dotted.name."""
    parts = name.split('.')
    parts_copy = parts[:]
    while parts_copy:
        try:
            module = __import__('.'.join(parts_copy))
            break
        except ImportError:
            del parts_copy[-1]
            if not parts_copy: raise
    parts = parts[1:]

    obj = module
    for part in parts:
        parent, obj = obj, getattr(obj, part)

    return obj



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