map-builtin-not-iterating reported with reduce()

[DylanYoung]

Steps to reproduce

1. Create reduce call with a map iterable
2. Observe pylint complain

Current behavior

1. W1636(map-builtin-not-iterating) is reported

Expected behavior

1. No error is reported (reduce is obviously an iterating context)

pylint --version output

pylint 1.9.5,
astroid 1.6.6
Python 2.7.16 (default, Apr 26 2019, 16:26:18)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.42.1)]

[DylanYoung]

Note: it looks like a similar bug was fixed here: #2731

But by the looks of it, I suspect it didn't touch either the Py2 case or the six case of using reduce (it explicitly check fro an 'itertools' root), but I could be mistaken.

[PCManticore]

Thanks for the report. Yeah, we'll need a separate solution for reduce.

[gyermolenko]

@DylanYoung
Could you please provide an example? I tried this one

print reduce(lambda x, y: x + y, map(str.upper, "abc"))

but didn't get your warning in results

[DylanYoung]

@gyermolenko Did you do a from six.moves import reduce?

It's possible that it works on Py3 too; I've only tested on Py2.

UPDATE: your example works if you add the import (which is to say, it replicates the bug)

UPDATE AGAIN: the six actually isn't necessary. I'm able to replicate with the code you've provided. Are you sure you have the py3k errors enabled? You can pass the --py3k flag to the CLI or update your config to include these errors.

[DylanYoung]

@PCManticore Moreover, I am still getting an error withitertools.chain:

from itertools import chain

d1, d2 = {}, {}

chain(d1.items(), d2.items())

[DylanYoung]

@PCManticore Also, a question, is there a config option to set other iterating contexts? This could be a good temporary work-around and is probably necessary to fully support this type of error code (dependent on the context of user code, which could be a c-extension that pylint knows nothing about). If there isn't, it might be worth thinking about before the EOL of Py2.

[PCManticore]

@DylanYoung Good question, there isn't, but it might be worthwhile to introduce a new option that accepts a list of iterable consuming functions.

[gyermolenko]

To summarize:

Warning in question ((map-builtin-not-iterating))

• appears only with --py3k option
• reproducible both for pylint 1.9.5 / python 2.7.16 with python2 example

print reduce(lambda x, y: x + y, map(str.upper, "abc"))

and for pylint 2.3.1 / python 3.7.4 with python3 example

from functools import reduce
print(reduce(lambda x, y: x + y, map(str.upper, "abc")))

• seems like "(using six or not)" can be removed from the title

====================================================

As for the second issue, with example

from itertools import chain
d1, d2 = {}, {}
chain(d1.items(), d2.items())

warning (dict-items-not-iterating) appears only for python2 and only with --py3k

[Pierre-Sassoulas]

Won't do, we removed the python3 porting mode in 2.11.