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multi-value-repeated-key-literal (F601)

Derived from the Pyflakes linter.

Fix is sometimes available.

What it does

Checks for dictionary literals that associate multiple values with the same key.

Why is this bad?

Dictionary keys should be unique. If a key is associated with multiple values, the earlier values will be overwritten. Including multiple values for the same key in a dictionary literal is likely a mistake.

Example

foo = {
    "bar": 1,
    "baz": 2,
    "baz": 3,
}
foo["baz"]  # 3

Use instead:

foo = {
    "bar": 1,
    "baz": 2,
}
foo["baz"]  # 2

Fix safety

This rule's fix is marked as unsafe because removing a repeated dictionary key may delete comments that are attached to the removed key-value pair. This can also change the program's behavior if the value expressions have side effects.

References