Patrick Maupin wrote:
This may or may not be relevant to 2.6 or 3.0 (because I don't have
those handy at the moment), but on 2.5 and earlier:
Python 2.5.2 (r252:60911, May 7 2008, 15:19:09)
[GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
print eval(compile('print "It works"\n', '', 'exec'))
It works
None
In 3.0b2,
print( eval(compile('print( "It works")\n', '', 'exec')))
does the same thing. So does
print( exec(compile('print( "It works")\n', '', 'exec')))
and I presume the exec statement would in 2.x.
Personally, I'm absolutely fine with this (because I have a use case,
naturally),
The only possible use I can think of would be is you are eval-ing
mixed-kind code objects:
def eval_and_go(cobj): # cobj = code object of whatever kind
x = eval(cobj)
if x is not None: # was not side-effect only
return g(x)
else:
return None
but eval() does work differently for compiled vs
non-compiled objects, and this behavior doesn't match what the doc at
http://docs.python.org/lib/built-in-funcs.html says, namely "This
function can also be used to execute arbitrary code objects (such as
those created by compile()). In this case pass a code object instead
of a string. The code object must have been compiled passing 'eval' as
the kind argument."
That doc statement is, itself, contradictory. How can it be an
"arbitrary code object" if it must have been compiled using 'eval'?
Perhaps all that is meant is "In order to return a result other than
None to eval's caller, the code object must have been compiled
passing 'eval' as the kind argument."
So, either the code or the doc should be fixed. I would vote +1 for
fixing the doc to match the code, but then I'm the sort of
dysfunctional programmer who sometimes has a use-case for expressions
with side-effects.
I filed a condensed version of this report, with my suggested added text, as
http://bugs.python.org/issue3569
tjr
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