John Snow <js...@redhat.com> writes:
> Mypy cannot understand that this match can never be None, so help it
> along.
>
> Signed-off-by: John Snow <js...@redhat.com>
> ---
> scripts/qapi/main.py | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/scripts/qapi/main.py b/scripts/qapi/main.py
> index 42517210b805..271d9e84da94 100644
> --- a/scripts/qapi/main.py
> +++ b/scripts/qapi/main.py
> @@ -23,7 +23,8 @@
>
> def invalid_prefix_char(prefix: str) -> Optional[str]:
> match = re.match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix)
@match can't be None because the regexp always matches a prefix,
possibly the empty prefix.
> - if match.end() != len(prefix):
> + # match cannot be None, but mypy cannot infer that.
> + if match and match.end() != len(prefix):
> return prefix[match.end()]
> return None
High-level logic:
if there is an invalid prefix character:
return it
return None
The actual code takes the return None when the match fails. If this
could happen, it would be wrong. I can't, so it doesn't matter, but I
dislike it anyway.
Alternative 1: turn "match cannot be None" from comment to code
match = re.match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix)
+ assert match
if match.end() != len(prefix):
return prefix[match.end()]
return None
Alternative 2: turn empty prefix into a special case
- match = re.match(r'([A-Za-z_.-][A-Za-z0-9_.-]*)?', prefix)
+ match = re.match(r'[A-Za-z_.-][A-Za-z0-9_.-]*', prefix)
+ if not match:
+ return prefix[0]
if match.end() != len(prefix):
return prefix[match.end()]
return None
I'd prefer alternative 1.
