On 2013-07-24, Peter Otten <__pete...@web.de> wrote:
>> So, my question boils down to: in Python 3 how is dict.keys()
>> different from dict? What are the use cases?
>
> I just grepped through /usr/lib/python3, and could not identify
> a single line where some_object.keys() wasn't either wrapped in
> a list (or set, sorted, max) call, or iterated over.
>
> To me it looks like views are a solution waiting for a problem.
Here's a case of using keys as a set-like view from my own
"production" code (i.e., I used it once for one important job):
seen = set()
students = {}
dates = []
for fname in sorted(glob.glob("currentterm201320?.csv")):
print(fname, end="\n\t")
date = get_date(fname)
dates.append(date)
term = fname[-11:-4]
r = reg.registration(term, path=".")
regs = r.keys()
for alt_id in regs & seen:
students[alt_id].append(r[alt_id])
for alt_id in seen - regs:
students[alt_id].append(None)
for alt_id in regs - seen:
students[alt_id] = [None]*(len(dates)-1) + [r[alt_id]]
seen.add(alt_id)
It was a very nice way to to do three different things depending
on the student sin the set I was working with, compared to a
registration list:
Granted the line was originally "regs = set(regs.keys())" before
it occurred to me that it sucked to take what must be equivalent
to a set, convert to a list, and then back to set again.
Thanks to the set-like view of dict.keys it worked just like one
might hope.
Looking at it again "seen" might be a redundant parallel version
of students.keys().
--
Neil Cerutti
--
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