[Python-Dev] one more restriction for from __future__ import ...

[Jeremy Hylton]

>>>>> "SM" == Skip Montanaro <skip@mojam.com> writes:

  Jeremy> The symbol table pass detects illegal future statements by
  Jeremy> comparing the current line number against the line number of
  Jeremy> the last legal futre statement.

  SM> Why not just add a flag (default false at the start of the
  SM> compilation) to the compiling struct that tells you if you've
  SM> seen a future-killer statement already?  Then if you see a
  SM> future statement the compiler can whine.

Almost everything is a future-killer statement, only doc strings and
other future statements are allowed.  I would have to add a
st->st_future_killed = 1 for almost every node type.

There are also a number of nodes (about ten) that can contain future
statements or doc strings or future killers.  As a result, I'd have to
add special cases for them, too.

Jeremy