[Python-bugs-list] [ python-Bugs-711268 ] A large block of commands after an "if" cannot be compiled

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Bugs item #711268, was opened at 2003-03-28 11:47
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https://sourceforge.net/tracker/?func=detail&atid=105470&aid=711268&group_id=5470

Category: Parser/Compiler
Group: Python 2.2.1
Status: Open
Resolution: None
Priority: 5
Submitted By: Bram Moolenaar (vimboss)
Assigned to: Nobody/Anonymous (nobody)
>Summary: A large block of commands after an "if" cannot be compiled

Initial Comment:
A Generated Python script Contains the code:
    if 1:
          file = bugreport.vim
          ... long list of commands ....

Executing this code with:
      exec cmds in globals(), globals()

Results in the error:
      SystemError: com_backpatch: offset too large

Looking into the code for com_backpatch() it appears
that the code is more than what can be jumped over.

Possible solutions:
1.  When there is too much code, use another jump
statement that allows for a larger offset.
2.  Always use a jump statement with a large offset
3.  When "if 1" is used, don't generate a jump
statement (not a real fix, but works for the situation
where I ran into the bug).

It looks like this bug exists in all versions of Python.

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>Comment By: Bram Moolenaar (vimboss)
Date: 2003-03-28 21:03

Message:
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user_id=57665

I can reproduce the problem with this text:
if 1:
   a = "a"

Repeat the assignment 7282 times.  Feed this text to "exec".
With 7281 assignments you do not get the error.
Looks like 9 bytes are produced per assignment.

Good luck fixing this!

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Comment By: Guido van Rossum (gvanrossum)
Date: 2003-03-28 20:18

Message:
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user_id=6380

Hm, the 32-bit argument doesn't work because of what
backpatch does. It would require a totally different
approach to allow backpatching a larer offset, or we'd
always have to reserve 4 bytes for the offset. :-(

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Comment By: Guido van Rossum (gvanrossum)
Date: 2003-03-28 20:13

Message:
Logged In: YES 
user_id=6380

Just curious. How big was the block of code?

Also, I wonder if the error message is bogus; opcode
arguments can now be 32 bits AFAIK.

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