dict-iter-missing-items (PLE1141)

Preview (since v0.3.0) · Related issues · View source

Derived from the Pylint linter.

Fix is always available.

This rule is unstable and in preview. The --preview flag is required for use.

What it does

Checks for dictionary unpacking in a for loop without calling .items().

Why is this bad?

When iterating over a dictionary in a for loop, if a dictionary is unpacked without calling .items(), it could lead to a runtime error if the keys are not a tuple of two elements.

It is likely that you're looking for an iteration over (key, value) pairs which can only be achieved when calling .items().

Example

data = {"Paris": 2_165_423, "New York City": 8_804_190, "Tokyo": 13_988_129}

for city, population in data:
    print(f"{city} has population {population}.")

Use instead:

data = {"Paris": 2_165_423, "New York City": 8_804_190, "Tokyo": 13_988_129}

for city, population in data.items():
    print(f"{city} has population {population}.")

Known problems

If the dictionary key is a tuple, e.g.:

d = {(1, 2): 3, (3, 4): 5}
for x, y in d:
    print(x, y)

The tuple key is unpacked into x and y instead of the key and values. This means that the suggested fix of using d.items() would result in different runtime behavior. Ruff cannot consistently infer the type of a dictionary's keys.

Fix safety

Due to the known problem with tuple keys, this fix is unsafe.