Convert string to Python class object?

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Given a string as user input to a Python function, I'd like to get a class object out of it if there's a class with that name in the currently defined namespace. Essentially, I want the implementation for a function which will produce this kind of result:

class Foo:
    pass

str_to_class("Foo")
==> <class __main__.Foo at 0x69ba0>

Is this, at all, possible?

python
10 Answers

This could work:

import sys

def str_to_class(classname):
    return getattr(sys.modules[__name__], classname)
user_1390220

Warning: eval() can be used to execute arbitrary Python code. You should never use eval() with untrusted strings. (See Security of Python's eval() on untrusted strings?)

This seems simplest.

>>> class Foo(object):
...     pass
... 
>>> eval("Foo")
<class '__main__.Foo'>
SLott_106610

You could do something like:

globals()[class_name]
user_908480 
import sys
import types

def str_to_class(field):
    try:
        identifier = getattr(sys.modules[__name__], field)
    except AttributeError:
        raise NameError("%s doesn't exist." % field)
    if isinstance(identifier, (types.ClassType, types.TypeType)):
        return identifier
    raise TypeError("%s is not a class." % field)

This accurately handles both old-style and new-style classes.

Evan_Fosmark_497010

Yes, you can do this. Assuming your classes exist in the global namespace, something like this will do it:

import types

class Foo:
    pass

def str_to_class(s):
    if s in globals() and isinstance(globals()[s], types.ClassType):
            return globals()[s]
    return None

str_to_class('Foo')

==> <class __main__.Foo at 0x340808cc>
user_1224550
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