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.