[New-bugs-announce] [issue35107] untokenize() fails on tokenize output when a newline is missing

[Gregory P. Smith]

New submission from Gregory P. Smith <greg at krypto.org>:

The behavior change introduced in 3.6.7 and 3.7.1 via https://bugs.python.org/issue33899 has further consequences:

```python
>>> tokenize.untokenize(tokenize.generate_tokens(io.StringIO('#').readline))
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File ".../cpython/cpython-upstream/Lib/tokenize.py", line 332, in untokenize
    out = ut.untokenize(iterable)
  File ".../cpython/cpython-upstream/Lib/tokenize.py", line 266, in untokenize
    self.add_whitespace(start)
  File ".../cpython/cpython-upstream/Lib/tokenize.py", line 227, in add_whitespace
    raise ValueError("start ({},{}) precedes previous end ({},{})"
ValueError: start (1,1) precedes previous end (2,0)
```

The same goes for using the documented tokenize API (`generate_tokens` is not documented):

```
tokenize.untokenize(tokenize.tokenize(io.BytesIO(b'#').readline))
...
ValueError: start (1,1) precedes previous end (2,0)

```

`untokenize()` is no longer able to work on output of `generate_tokens()` if the input to generate_tokens() did not end in a newline.

Today's workaround: Always append a newline if one is missing to the line that the readline callable passed to tokenize or generate_tokens returns.  Very annoying to implement.

----------
messages: 328876
nosy: ammar2, gregory.p.smith, meador.inge, taleinat, terry.reedy
priority: normal
severity: normal
status: open
title: untokenize() fails on tokenize output when a newline is missing
versions: Python 3.6, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue35107>
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