[issue9974] tokenizer.untokenize not invariant with line continuations

[Brian Bossé]

New submission from Brian Bossé <penrif at gmail.com>:

Executing the following code against a py file which contains line continuations generates an assert:
import tokenize
foofile = open(filename, "r")
tokenize.untokenize(list(tokenize.generate_tokens(foofile.readline)))

(note, the list() is important due to issue #8478)

The assert triggered is:
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Python27\lib\tokenize.py", line 262, in untokenize
    return ut.untokenize(iterable)
  File "C:\Python27\lib\tokenize.py", line 198, in untokenize
    self.add_whitespace(start)
  File "C:\Python27\lib\tokenize.py", line 187, in add_whitespace
    assert row <= self.prev_row
AssertionError

I have tested this in 2.6.5, 2.7 and 3.1.2.  The line numbers may differ but the stack is otherwise identical between these versions.

Example input code:
foo = \
   3

If the assert is removed, the code generated is still incorrect.  For example, the input:
foo = 3
if foo == 5 or \
   foo == 1
    pass

becomes:
foo = 3
if foo == 5 orfoo == 1
    pass

which besides not having the line continuation, is functionally incorrect.

I'm wrapping my head around the functionality of this module and am willing to do the legwork to get a fix in.  Ideas on how to go about it are more than welcome.

Ironic aside:  this bug is present when tokenize.py itself is used as input.

----------
components: Library (Lib)
messages: 117538
nosy: Brian.Bossé
priority: normal
severity: normal
status: open
title: tokenizer.untokenize not invariant with line continuations
type: behavior
versions: Python 2.6, Python 2.7, Python 3.1

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue9974>
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