Bugs item #1167751, was opened at 2005-03-21 09:47
Message generated for change (Comment added) made by nnorwitz
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Category: Parser/Compiler
Group: Python 2.5
>Status: Closed
>Resolution: Fixed
Priority: 8
Submitted By: John Ehresman (jpe)
>Assigned to: Anthony Baxter (anthonybaxter)
Summary: Argument genexp corner case
Initial Comment:
The following raises an unexpected exception; I would
expect it to either work or raise a SyntaxError. It
seems that the grammar parses it, but the compiler does
not do the right thing.
>>> def foo(a): pass
>>> foo(a = i for i in range(10))
Traceback (most recent call last):
File "<stdin>", line 1, in ?
NameError: name 'i' is not defined
foo(a = (i for i in range(10)) works.
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>Comment By: Neal Norwitz (nnorwitz)
Date: 2005-10-20 23:27
Message:
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Checked in as:
* Python/graminit.c 2.41
* Lib/test/test_genexps.py 1.10
* Grammar/Grammar 1.55
* Misc/NEWS 1.1392 and 1.1391
Leaving it up to Anthony whether this should be backported.
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Comment By: Nick Coghlan (ncoghlan)
Date: 2005-10-11 06:43
Message:
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The problem is definitely on the parser end though:
Py> compiler.parse("foo(x=i for i in range(10))")
Module(None, Stmt([Discard(CallFunc(Name('foo'),
[Keyword('x', Name('i'))], None, None))]))
It's getting to what looks like a valid keyword argument in
"x=i" and throwing the rest of it away, when it should be
flagging a syntax error (the parser's limited lookahead
should be enough to spot the erroneous 'for' keyword and
bail out).
The problem's actually worse than the OP noted: consider
what will happen if there is a variable "i" visible from the
location of the function call (e.g. from a list
comprehension or for loop in a nested scope). Good luck
tracking that one down. . .
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Comment By: Neal Norwitz (nnorwitz)
Date: 2005-10-10 21:10
Message:
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I definitely agree this is a big problem.
Here's what the code above generates:
2 0 LOAD_GLOBAL 0 (foo)
3 LOAD_CONST 1 ('a')
6 LOAD_GLOBAL 1 (i)
9 CALL_FUNCTION 256
12 POP_TOP
13 LOAD_CONST 0 (None)
16 RETURN_VALUE
If I put parens around the genexp, I get:
2 0 LOAD_GLOBAL 0 (foo)
3 LOAD_CONST 1 ('a')
6 LOAD_CONST 2 (<code object
<generator expression> at 0x2a960baae8, file "<stdin>", line 2>)
9 MAKE_FUNCTION 0
12 LOAD_GLOBAL 1 (range)
15 LOAD_CONST 3 (10)
18 CALL_FUNCTION 1
21 GET_ITER
22 CALL_FUNCTION 1
25 CALL_FUNCTION 256
28 POP_TOP
29 LOAD_CONST 0 (None)
32 RETURN_VALUE
----------------------------------------------------------------------
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