Yury Selivanov wrote:
> BTW we already have mechanisms to always propagate context to the
> caller -- just use threading.local() or a global variable.
But then you don't have a way to *not* propagate the
context change when you don't want to.
Here's my suggestion: Make an explicit distinction between
creating a new binding for a context var and updating an
existing one.
So instead of two API calls there would be three:
contextvar.new(value) # Creates a new binding only
# visible to this frame and
# its callees
contextvar.set(value) # Updates existing binding in
# context inherited from caller
contextvar.get() # Retrieves the current binding
If we assume an extension to the decimal module so
that decimal.localcontext is a context var, we can
now do this:
async def foo():
# Establish a new context for this task
decimal.localcontext.new(decimal.Context())
# Delegate changing the context
await bar()
# Do some calculations
yield 17 * math.pi + 42
async def bar():
# Change context for caller
decimal.localcontext.prec = 5
--
Greg
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