On: The PEPs of Python 3.9

[nomel]

That byte code is then interpreted at runtime, so the meaning of s.upper() could change. What something does, when it’s parsed, is not fixed.

You can definitely catch most cases at runtime. I’ve done something like this, in an library, to catch a case where people were treating the copy of data as a mutable view.

    interface[address][slice] = new_values # fancy noop

Where a read, modify, write was required:

    byte_values = interface[address]
    byte_values[slice] = new_values
    interface[address] = byte_values

It would log/raise a useful error if the there was no assignment/passing of the return value.