[LNT] Python 3 support: adapt to zip returning an iterator

[thopre]

Summary

zip() returns a list in Python 2 but an iterator in Python 3.
Fortunately, the only use is in the return statement in pairs() and the
only call site of pairs() iterates over the result. This commit thus
adds a docstrings for pairs to make it clear callers can only rely on
the result being iterable. It also rename the parameter to not conflict
with the list builtin function.

[hubert.reinterpretcast]

lnt/server/reporting/analysis.py

375 ↗

(On Diff #220977)

The unpacking works without this change even in Python 3.

lnt/tests/nt.py

793 ↗

(On Diff #220977)

I believe this change is unnecessary. The constructor will fully visit the result of zip.

[thopre]

Cancelling this patch since all users of zip are fine with iterable (pairs is only used in dailyreport.py in a foreach statement).

[thopre]

Add comments to pairs() stating it returns an iterable.

[hubert.reinterpretcast]

LGTM with suggestion to update commit message.

lnt/server/reporting/report.py

11

I agree that a rename would help. Please update the commit message with the rationale.

lnt/server/reporting/report.py

 """
 Common functions and classes that are used by reports.
 """
 
 import colorsys
 
 from collections import namedtuple
 
 OrderAndHistory = namedtuple('OrderAndHistory', ['max_order', 'recent_orders'])
 
-def pairs(list):
-    return zip(list[:-1], list[1:])
+def pairs(l):
+    """Make an iterable of all pairs of consecutive elements in l."""
+    return zip(l[:-1], l[1:])
 
 # The hash color palette avoids green and red as these colours are already used
 # in quite a few places to indicate "good" or "bad".
 _hash_color_palette = (
     colorsys.hsv_to_rgb(h=45. / 360, s=0.3, v=0.9999),  # warm yellow
     colorsys.hsv_to_rgb(h=210. / 360, s=0.3, v=0.9999),  # blue cyan
     colorsys.hsv_to_rgb(h=300. / 360, s=0.3, v=0.9999),  # mid magenta
     colorsys.hsv_to_rgb(h=150. / 360, s=0.3, v=0.9999),  # green cyan