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Currently, there's a discrepancy in the exception reporting for the `.index` and `.remove` methods of many objects:
For arrays:
 array.remove(val) -> ValueError: array.remove(x): x not in list 
 array.index(val) -> ValueError: array.index(x): x not in list
not only is always printing `x` not in list not informative, it's wrong since it isn't a list.
For tuples:
 tuple.index(val) -> ValueError: tuple.index(x): x not in tuple
For lists:
 list.remove(val) -> ValueError: list.remove(x): x not in list
list.index(val) produces a more informative message: ValueError: <val> is not in list
For deques:
 deque.remove(val) -> ValueError: deque.remove(x): x not in deque
similarly to lists, `deque.index(val)` prints the actual argument supplied.
I'm not sure if there's valid reasoning behind not providing the repr of the arguments in all `remove` methods but, if there isn't, I'd like to suggest changing all of them to use PyErr_Format and produce more informative messages:
 array.remove(val) -> ValueError: <val> is not in array 
 array.index(val) -> ValueError: <val> is not in array
 tuple.index(val) -> ValueError: <val> is not in tuple
 list.remove(val) -> ValueError: <val> is not in list
 deque.remove(val) -> ValueError: <val> is not in deque

I'd be happy to supply a PR for this if the change seems reasonable.