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(#2) Conditionalized #import behavior
=====================================
:CHEP: 2
:Title: Conditionalized #import behavior
:Version: 1
:Author: R Tyler Ballance <tyler at slide.com>
:Status: Draft
:Type: Standards Track
:Content-Type: text/x-rst
:Created: 07-Jun-2009
----
Abstract
--------
This CHEP proposes an update to the way the #import and #from
directives are handled such that locally scoped imports and
module-level imports are handled appropriately.
Motivation
----------
Currently Cheetah (v2.2.1) provides two different, but mutually exclusive,
means of importing Python modules with the #from/#import directives. The
"traditional" handling for #from/#import is that the generated import
statements shall all be relocated to the top of the generated module's
source code, i.e. ::
#import cjson
Hello $cjson.encode([1, 2, 3])
Will result in generated module code along the lines of::
import cjson
class Foo(Template):
def writeBody(self):
write('Hello ')
write(cjson.encode([1, 2, 3]))
Also currently in Cheetah is the ability to switch off this
behavior and enable location specific #from/#import handling
in the generated code, with this block of Cheetah for example::
#def aFunction(arg)
#try
#from hashlib import md5
#except ImportError
#from md5 import md5
#end try
#return $md5.new(arg).hexdigest()
#end def
Will result in code generated with everything in
place such that the Python looks something like::
class Foo(Template):
def aFunction(self, arg):
try:
from hashlib import md5
except ImportError:
from md5 import md5
return md5.new(arg).hexdigest()
These two approaches to handling the #from/#import directives
are both beneficial for different situations but currently they
are handled in mutually exclusive code paths and in mutually
exclusive fashions.
Specification
-------------
Rationale
---------
Backwards Compatibility
-----------------------
Reference Implementation
------------------------
Copyright
---------
This document has been placed in the public domain.
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