False positive unnecessary-dict-index-lookup and consider-using-dict-items if value associated with key is changed in loop

[akosthekiss]

Steps to reproduce

Given a file d.py:

"""d.py"""

d = {'key': 'value'}

print(d)

for k, _ in d.items():
    d[k] += 'VALUE'
    if 'V' in d[k]:  # if d[k] is replaced with _, the semantics change
        print('found V')

print(d)

for k in d:  # if this gets rewritten to d.items(), we are back to the above problem
    d[k] += '123'
    if '1' in d[k]:
        print('found 1')

print(d)

Current behavior

Result of pylint d.py:

************* Module d
d.py:9:14: R1733: Unnecessary dictionary index lookup, use '_' instead (unnecessary-dict-index-lookup)
d.py:14:0: C0206: Consider iterating with .items() (consider-using-dict-items)

Expected behavior

No diagnostics.

Following the recommendation for line 9 (i.e., rewriting d[k] to _) would incorrectly change the semantics of the program, as d[k] has already been changed, so it has a different value than _.

Following the recommendation for line 14 (i.e., rewriting for k in d to for k, v in d.items() would lead back to the above problem.

pylint --version output

Result of pylint --version output:

pylint 3.0.0-a4
astroid 2.6.1
Python 3.6.9 (default, Jan 26 2021, 15:33:00) 
[GCC 8.4.0]

pylint 2.9.0
astroid 2.6.1
Python 3.6.9 (default, Jan 26 2021, 15:33:00) 
[GCC 8.4.0]

[cdce8p]

@yushao2 Would you like to take a look at it? It seems we need to ignore unnecessary-dict-index-lookup and consider-using-dict-items if an Assign or AugAssign is used.

[yushao2]

@yushao2 Would you like to take a look at it? It seems we need to ignore unnecessary-dict-index-lookup and consider-using-dict-items if an Assign or AugAssign is used.

raised a pr for it: #4640