CODEWITHSUNDEEP
python
scribu
scribu

Reputation: 3078

Get type instance from string in Python

So, I need to cast a value to a given type:

if 'int' == type_name:
    value = int(value)
elif 'str' == type_name:
    value = str(value)
...

Is there a way to do that generically? E.g.:

type_instance = get_type_instance(type_name)
value = type_instance(value)

I'm using Python 2.7, but would be interested in a Python 3.X solution as well.

Update:

Here's the solution I'm using:

class Token:

    def __init__(self, type_name, value):
        self.type = type_name
        self.value = __builtins__[type_name](value) # not safe

This is just a toy parser. Don't use in production!

Upvotes: 6

Views: 3633

Answers (3)

Chinmay Kanchi
Chinmay Kanchi

Reputation: 66003

Since you specified float64 in an earlier version of the question, I assumed you were also interested in getting numpy types. If so, the following function should solve this:

def can_typecast(type, value):        
    try:
        tp = getattr(__builtins__, type)
    except AttributeError:
        try:
            np = __import__('numpy')
            tp = getattr(np, type)
            if not isinstance(tp, type):
                raise ValueError('type string is not a type')
        except AttributeError:
            raise ValueError('Invalid type specified')
        except ImportError:
            raise ValueError('Numpy not found')
    try:
        tp(value)
    except ValueError:
        return False
    return True

What this does is it first looks to see if the given type name can be resolved to a built-in type. If that fails, it looks to see if the type name can be found in numpy and if it is a valid type object and if so, tries the cast operation on that.

Upvotes: 0

Oleksii Kachaiev
Oleksii Kachaiev

Reputation: 6232

If you need only __builtins__ types you can do

value = getattr(__builtins__, type_name)(value)

Upvotes: 7

user2665694
user2665694

Reputation:

Build a dict

TYPES = {
  'int' : int,
  'str' : str,
...
}

value = TYPES[type_name](value)

Upvotes: 7

Related Questions