I'm missing something here...

[Skip Montanaro]

Here's a dumb little bit of code, adapted from a slightly larger script:

#!/usr/bin/env python

"dummy"

import glob
import os

def compare_prices(*_args):
    "dummy"
    return set()

def find_problems(cx1, cx2, cx3, prob_dates):
    "dummy"
    for fff in sorted(glob.glob("/path/to/*.nrm")):
        sym = os.path.splitext(os.path.basename(fff))[0]
        prob_dates |= compare_prices("E:%s"%sym, cx1, cx2, cx3)

When I run pylint against it, it complains:

junk.py:10: [W0613(unused-argument), find_problems] Unused argument 'prob_dates'

I must be misunderstanding something about the |= operator as applied
to sets. If I read the docs correctly, s1 |= s2 is equivalent to
s1.update(s2). A dumb "test" at the prompt suggests that's true:

>>> s1 = set("abc")
>>> s2 = set("cde")
>>> s1 | s2
set(['a', 'c', 'b', 'e', 'd'])
>>> s1 |= s2
>>> s1
set(['a', 'c', 'b', 'e', 'd'])
>>> s1 = set("abc")
>>> s1.update(s2)
>>> s1
set(['a', 'c', 'b', 'e', 'd'])

If I change the last line of find_problems to call
prob_dates.update(), the message disappears. Why is pylint (1.4.2 BTW)
complaining that the prob_dates argument of find_problems is unused
when I use the |= operator?

Thx,

Skip