[Python-Dev] from future syntax changed (original) (raw)

Tim Peters tim.peters at gmail.com
Tue Jan 31 06:53:26 CET 2006

[Guido van Rossum]

It looks like the syntax for "from future import ..." changes in Python 2.5. I was playing around with Cheetah, and it stumbled over a file with the following structure:

# comments """ docstring """ author = "..." version = "..." from future import generators Python 2.2 throug 2.4 accept this fine. Perhaps the AST tree enforces stricter syntax for what can precede a future statement? I think this should be fixed.

Peculiar. It wasn't intended that be allowed; PEP 236 spelled this out:

"""" In addition, all future_statments must appear near the top of the module. The only lines that can appear before a future_statement are:

+ The module docstring (if any).
+ Comments.
+ Blank lines.
+ Other future_statements.

""""

That isn't frivolous, since a future gimmick may affect the legality of binding statements (as in your example) or other import statements, etc -- it was deliberate that only blank lines, comments and (maybe) a docstring could appear before the first future statment. I'd call this a bug in 2.2-2.4.

Note too that Tools/scripts/cleanfuture.py in 2.4 doesn't change that example, because it doesn't believe it contains any future statements (cleanfuture.py follows the PEP's syntax).

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