rspec/rules/S5650/python/rule.adoc

This rule raises an issue when the object of a ``++with++`` statement is not a valid a context manager.

== Why is this an issue?

The https://docs.python.org/3/reference/compound_stmts.html#the-with-statement[``++with++`` statement] is used to wrap the execution of a block with methods defined by a context manager. The https://docs.python.org/3/reference/datamodel.html#context-managers[context manager] handles the entry into, and the exit from, the desired runtime context for the execution of the block of code. To do so, a context manager should have an ``++__enter__++`` and an ``++__exit__++`` method.

Executing the  following block of code:

[source,python]
----
class MyContextManager:
    def __enter__(self):
        print("Entering")

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Exiting")


with MyContextManager():
    print("Executing body")
----

will output:
[source,text]
----
Entering
Executing body
Exiting
----

If either the ``++__enter__++`` or the ``++__exit__++`` method is missing, an ``AttributeError`` will be raised instead.


=== Note 
When working with https://docs.python.org/3/reference/datamodel.html#async-context-managers[asynchronous context managers], the ``with`` statement should be replaced by ``++async with++``.

== How to fix it

To fix this issue, make sure that the object of the `with` statement is a valid context manager (implementing both ``++__enter__++`` and ``++__exit__++`` methods).

If the object of the `with` statement is an asynchronous context manager, make sure to use an `async with` statement.

== Code examples

=== Noncompliant code example

[source,python,diff-id=1,diff-type=noncompliant]
----
class MyContextManager:
    ...

with MyContextManager():  # Noncompliant: not a valid contex manager
    ...

def simple_contextmanager():
    ...

with simple_contextmanager() as e:  # Noncompliant: not a valid contex manager
    ...

@asynccontextmanager
async def async_context_manager():
    yield 42

def call_async_context_manager():
    with async_context_manager() as context:  # Noncompliant: missing "async"
        ...

----


=== Compliant solution

[source,python,diff-id=1,diff-type=compliant]
----
class MyContextManager:
    def __enter__(self):
        print("Entering")

    def __exit__(self, exc_type, exc_val, exc_tb):
        print("Exiting")


with MyContextManager():
    ...

from contextlib import contextmanager, asynccontextmanager

@contextmanager
def simple_contextmanager():
    print("enter")
    yield
    print("exit")

with simple_contextmanager() as e:
    ...

@asynccontextmanager
async def async_context_manager():
    yield 42

async def call_async_context_manager():
    async with async_context_manager() as context:
        ...
----

== Resources

=== Documentation

* Python Documentation - https://docs.python.org/3/reference/compound_stmts.html#the-with-statement[``++with++`` statement]
* Python Documentation - https://docs.python.org/3/reference/datamodel.html#context-managers[context managers]


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

* Replace this expression with a context manager.
* Add "async" before "with"; Expression is an async context manager.


=== Highlighting

Primary: the expression used as a context manager

Secondary: the "with" keyword


endif::env-github,rspecator-view[]