[Python-Dev] PEP 318 - generality of list; restrictions on elements (original) (raw)

Jewett, Jim J jim.jewett at eds.com
Mon Mar 8 14:21:34 EST 2004

Given that some syntax will be chosen, what are the restrictions on the wrappers?

Right now, the variable portion of the syntax is:

'[' wrapper (, wrapper)* ']'

What else should be accepted, to avoid surprises?

Variables that evaluate to a list?
Expressions that evaluate to a list?
List comprehensions?
Single wrappers?

What are the restrictions on list items?

Only a function?
Only a code object?  (I assume so)
Must the code return the original function?
Must the code return a code object?

In other words, which of the following examples should work, which should fail, and which should depend on whatever is easiest?

  1. fail, integer not a callable? (Don't try to slice the args!)

    def name(args)[0]:

  2. fail, as w[0] is itself a (non-callable) list?

    w = [wrapper] def name(args) [w]:

  3. fail, not a list?

    def name(args) classmethod:

  4. ??? lambda would be OK, except for the second ":"

    def name(args)[lambda x: x]:

  5. should succeed?

    def name(args)[x for x in decorators if x in active]:

  6. ??? wrapper does not return a callable.

    y = lambda x: None def name(args) [y]:

  7. a list, but no '[]'. either surprises.

    def name(args) list((wrap1, wrap2)):

  8. a list, but no '[]'. either surprises.

    w = [wrapper] def name(args) w:

  9. a list, but no '[]'. either surprises.

    def w(): return [y,y,y] def name(args) w():

Do the wrappers have to be defined when the definition starts? Just defined before the module finishes its definition? Before the definition is executed? In other words, are these OK?

def outer(): # w not defined at module load, but defined before any call def inner(x)[w]: print x return inner

But if that is OK, then which w would be used in the next example? w is redefined "later", but before inner is actually called.

def w(fn): print "outside w" return fn

def outer(): # w not defined yet, but defined in this def inner(x)[w]: print x def w(fn): return fn inner(5)

How about this? There is no guarantee that othermod will finish loading first, though I suppose that already causes problems today.

import othermod def fn()[othermod.wrap]: pass

-jJ

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