[ python-Bugs-1333982 ] Bugs of the new AST compiler

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Bugs item #1333982, was opened at 2005-10-21 10:08
Message generated for change (Comment added) made by arigo
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Category: Parser/Compiler
Group: AST
Status: Open
Resolution: None
Priority: 5
Submitted By: Armin Rigo (arigo)
Assigned to: Nobody/Anonymous (nobody)
Summary: Bugs of the new AST compiler

Initial Comment:
The newly merged AST branch is likely to expose
a number of small problems before it stabilizes,
so here is a tentative bug tracker entry to
collect such small problems.


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>Comment By: Armin Rigo (arigo)
Date: 2005-10-21 12:33

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I would suspect the following one to be due to incorrect
handling of EXTENDED_ARG -- it's from a PyPy test about that:

longexpr = 'x = x or ' + '-x' * 2500
code = '''
def f(x):
    %s
    %s
    %s
    %s
    %s
    %s
    %s
    %s
    %s
    %s
    while x:
        x -= 1
        # EXTENDED_ARG/JUMP_ABSOLUTE here
    return x
''' % ((longexpr,)*10)

exec code
f(5)
SystemError: unknown opcode

dis.dis() shows that the target of both the SETUP_LOOP and
the JUMP_IF_FALSE at the start of the loop are wrong.

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Comment By: Armin Rigo (arigo)
Date: 2005-10-21 12:15

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The Python rules about which names get mangled are a bit
insane.  I share mwh's view that mangling should never have
been invented in the first place, but well:

>>> def f():
...   __x = 5
...   class X:
...     def g(self):
...       return __x
...   return X
... 
Fatal Python error: unknown scope for _X__x in X(135832776)
in <stdin>


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Comment By: Armin Rigo (arigo)
Date: 2005-10-21 12:01

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For reference, an optimization that got lost:

    def f():
        'a'
        'b'

'a' is the docstring, but the 'b' previously did not show
up anywhere in the code object.  Now there is the
LOAD_CONST/POP_TOP pair.

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Comment By: Armin Rigo (arigo)
Date: 2005-10-21 11:54

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any reason why lambda functions have a __name__ of
'lambda' now instead of '<lambda>' ?

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Comment By: Armin Rigo (arigo)
Date: 2005-10-21 10:22

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import a as b, c

the 'c' part gets completely forgotten and there is
no 'IMPORT_NAME c' in the bytecode.

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Comment By: Armin Rigo (arigo)
Date: 2005-10-21 10:13

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A scoping problem (comparing with the old compiler):

class X:
    print hello

The variable 'hello' is incorrectly looked up with
LOAD_GLOBAL instead of LOAD_NAME.  It causes a crash
in PyPy in a case where the name 'hello' is stored
into the class implicitely (via locals()).  It can
probably be discussed if the bug is in PyPy, but it
is a difference in behavior.

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