I was writing some code and made a typo, but it didn't error. Tracing it back, I found out that these work:

>>> [] = []
>>> () = ()
>>> 

This is iterable unpacking, but with no real target for assignment. Why does Python allow this? Are there situations where this is useful?

Here's where it's defined in the grammar. I would have thought you'd need at least one identifier, attributeref, subscription, or slicing, but apparently not; target_list is optional inside parentheses or brackets.

target ::=  identifier
            | "(" [target_list] ")"
            | "[" [target_list] "]"
            | attributeref
            | subscription
            | slicing
            | "*" target

Looking at the documentation history, this wasn't possible as recently as Python 3.4 and 2.6, but assigning to [] was added in Python 3.5 and 2.7, and () in Python 3.6.

Related:

• Why is it valid to assign to an empty list but not to an empty tuple? (The answer was ultimately a bug)
• Why isn't assigning to an empty list (e.g. [] = "") an error? (Answers talk more about how than why)

Note: Since I'm asking about a design choice, answers should include references to authoritative sources like official documentation or a core dev.