Is it possible to dynamic instantiate a class written in a string without the need to write it to a file?

How can I instantiate the class stored in the raw string my_class without having to save this string into a file first?

my_class = r'''class A:
    def print(self):
        print('Hello World')
    '''

my_class_object = string_to_class()

my_class_object.print()

In the code above, I'm looking for an implementation of the function string_to_class() that returns an object of the class inside my_class.

The expected output of the code above is Hello World.

Solution

You just need to use exec: it supports dynamic execution of Python code.

import re 
def string_to_object(str_class, *args, **kwargs):
    exec(str_class)
    class_name = re.search("class ([a-zA-Z_][a-zA-Z0-9_]*)", str_class).group(1)
    return locals()[class_name](*args, **kwargs)

You can use the string_to_object function to automatically create an object of the specified class:

my_class = '''
class A:
    def print(self):
        print("Hello World")
'''
a = string_to_object(my_class)
a.print() # Hello World

You can also build something more complicated:

my_class = '''
class B:
    def __init__(self, a, b, c=0, d=1):
        self.a = a
        self.b = b
        self.c = c
        self.d = d
'''
b = string_to_object(my_class, 4, 5, c=7)
print(b.a) # 4
print(b.b) # 5
print(b.c) # 7
print(b.d) # 1

And also:

class C:
    pass

my_class = '''
class D(C):
    pass
'''

d = string_to_object(my_class)