how to access object's method inside a with statement?

Question

I am trying to create a class to be used with the 'with' statement in python 3 but inside the 'with' statement I don't have access to the object or the methods. For example, Running the following code:

class Openizer:

    def __init__(self, something):
        self._something = something

    def __enter__(self):
        print('entered')

    def __exit__(self, exc_type, exc_value, traceback):
        print('exited')

    def print_something(self):
        print(self._something)


with Openizer('something') as op:
    op.print_something()

raises the following exception:

Traceback (most recent call last):
  File "openizer.py", line 16, in <module>
    op.print_something()
AttributeError: 'NoneType' object has no attribute 'print_something'

If I try to print(op) it prints 'None'. Why is that? am I using the with statement wrong? what is the correct way? Is it possible to instantiate a class with the 'with' statement and inside the 'with' statement call the instantiated object's methods?

Consider the open() function, it instantiated a file object which can than be read from or written to, I'd like to do something similar.

You never return anything in your `__enter__` method, so it implicitly returns `None` — juanpa.arrivillaga, Sep 09 '18 at 18:52

score 0 · Answer 1 · answered Sep 09 '18 at 19:05

0

__enter__() should return self. Whatever gets returned from __enter__ goes to the as clause.

answered Sep 09 '18 at 19:05

Bharel

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how to access object's method inside a with statement?

1 Answers1