Yury Selivanov wrote:
It would be great if you or Greg could show a couple of real-world
examples showing the "issue" (with the current PEP 550
APIs/semantics).
Here's one way that refactoring could trip you up.
Start with this:
async def foo():
calculate_something()
#in a coroutine, so we can be lazy and not use a cm
ctx = decimal.getcontext().copy()
ctx.prec = 5
decimal.setcontext(ctx)
calculate_something_else()
And factor part of it out (into an *ordinary* function!)
async def foo():
calculate_something()
calculate_something_else_with_5_digits()
def calculate_something_else_with_5_digits():
ctx = decimal.getcontext().copy()
ctx.prec = 5
decimal.setcontext(ctx)
calculate_something_else()
Now we add some more calculation to the end of foo():
async def foo():
calculate_something()
calculate_something_else_with_5_digits()
calculate_more_stuff()
Here we didn't intend calculate_more_stuff() to be done
with prec=5, but we forgot that calculate_something_else_
with_5_digits() changes the precision and *doesn't restore
it* because we didn't add a context manager to it.
If we hadn't been lazy and had used a context manager in the
first place, that wouldn't have happened.
Summary: I think that skipping context managers in some
circumstances is a bad habit that shouldn't be encouraged.
--
Greg
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