Non-threadsafe Dynamic Scoping in python

test-deep.py

#encoding=utf-8

def env(name):
    return stacks_of_names[name][-1]

stacks_of_names = {}

# comment the below line?
__builtins__.env = env 

class assign(object):
    def __init__(self, name, value):
        self.name = name
        self.value = value

    def __enter__(self):
        stack = stacks_of_names.setdefault(self.name, []) 
        stack.append(self.value)

    def __exit__(self, *args):
        stacks_of_names[self.name].pop()

if __name__ == '__main__':
    # do a demo
    def outp(msg):
        if env('lang') == 'pt_PT':
            print('olá' if msg == 'hi' else 'adeus lel')
        else:  # default
            print(msg)

    def eng_section():
        with assign('lang', 'en'):
            program()

    def program():
        outp('hi')
        outp('bye')

    with assign('lang', 'pt_PT'):
        program()
        eng_section()