Terry Reedy wrote:
On 6/12/2011 6:30 PM, Greg Ewing wrote:
I'm -1 on any proposal that somehow tries to make the default-argument hack more acceptable.
The main reason people still feel the need to use it is that the for-loop is broken, insofar as it doesn't create a new binding for each iteration.
The right way to address that is to fix the for-loop,
Or use closures, which were partly designed to replace default arg use.
Default args are specifically used in at least one use-case where closures give the wrong result.
funcs = [lambda x: x+i for i in range(10)] funcs[0].__closure__ # may be different in Python 2.x (<cell at 0xb7bd8a1c: int object at 0x81b20c0>,) funcs[0](42) # should return 42+0 51
The usual solution is to *not* use a closure:
funcs = [lambda x, i=i: x+i for i in range(10)] funcs[0].__closure__ is None True funcs[0](42) 42 funcs[9](42) 51
This case is quite different from the multiple capture in for-loop case. The OP is simply trying to localize names for speed instead of using module constants, which would otherwise do quite fine and are routinely used in the stdlib.
That's just one use-case. Jan gave two others. Optimizations might be common in the stdlib, but it's a hack, and an ugly one. Function parameters should be kept for actual arguments, not for optimizing name look-ups. -- Steven