> But should not this patch be handled in a way wherein.
> key.capitalize() is just replaced by key.upper()?

Hmm, are you sure?
>>> "hello".upper()
'HELLO'
>>> 

but the issue is with values containing dashes:
>>> 'accept-charset'.capitalize()
'Accept-charset'
whereas the rest of the world would expect:
'Accept-Charset'
        ^

This is especially useful, if you try to emulate the behavior of a
typical browser as close as possible.