Lexical cast from string to type

I like using locate, which works on built-in types:

>>> from pydoc import locate>>> locate('int')<type 'int'>>>> t = locate('int')>>> t('1')1

...as well as anything it can find in the path:

>>> locate('datetime.date')<type 'datetime.date'>>>> d = locate('datetime.date')>>> d(2015, 4, 23)datetime.date(2015, 4, 23)

...including your custom types:

>>> locate('mypackage.model.base.BaseModel')<class 'mypackage.model.base.BaseModel'>>>> m = locate('mypackage.model.base.BaseModel')>>> m()<mypackage.model.base.BaseModel object at 0x1099f6c10>

You're a bit confused on what you're trying to do. Types, also known as classes, are objects, like everything else in python. When you write int in your programs, you're referencing a global variable called int which happens to be a class. What you're trying to do is not "cast string to type", it's accessing builtin variables by name.

Once you understand that, the solution is easy to see:

def get_builtin(name):    return getattr(__builtins__, name)

If you really wanted to turn a type name into a type object, here's how you'd do it. I use deque to do a breadth-first tree traversal without recursion.

def gettype(name):    from collections import deque    # q is short for "queue", here    q = deque([object])    while q:        t = q.popleft()        if t.__name__ == name:            return t        else:            print 'not', t        try:            # Keep looking!            q.extend(t.__subclasses__())        except TypeError:            # type.__subclasses__ needs an argument, for whatever reason.            if t is type:                continue            else:                raise    else:        raise ValueError('No such type: %r' % name)

Why not just use a look-up table?

known_types = {    'int': int,    'float': float,    'str': str    # etc}var_type = known_types['int']