AttributeError: __enter__ Not Defined

Why This Happens

The 'with' statement requires the object to be a context manager with __enter__ and __exit__ methods. If you use 'with' on a regular object, Python raises this error.

The Problem

class Connection:
    def connect(self):
        return self

with Connection() as conn:
    pass

The Fix

class Connection:
    def __enter__(self):
        self.connect()
        return self
    def __exit__(self, *args):
        self.close()
        return False
    def connect(self): pass
    def close(self): pass

with Connection() as conn:
    pass

Step-by-Step Fix

1. 1

   Implement context manager protocol

   Add __enter__ and __exit__ methods.

2. 2

   Use contextlib

   Use @contextlib.contextmanager to create context managers from generators.

3. 3

   Check the object type

   Verify the object supports context management.