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[commands] Allow for backtracking parsing with typing.Optional

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Original code by zephyrkul.

This new parsing mode allows for backtracking in case of failure
when a typing.Union[..., NoneType] or a typing.Optional[...] is used.
This means that if a type would fail to parse, the view is undo'd to
a previous state, passing the default parameter to the callback, and
then continuing on the next parameter as if nothing had happened.
This commit is contained in:
Rapptz 2018-09-23 06:12:26 -04:00
parent 8ef509883a
commit 00a445310b
1 changed files with 10 additions and 0 deletions
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10
discord/ext/commands/core.py
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@ -281,7 +281,15 @@ class Command:
else:
if origin is typing.Union:
errors = []
_NoneType = type(None)
for conv in converter.__args__:
# if we got to this part in the code, then the previous conversions have failed
# so we should just undo the view, return the default, and allow parsing to continue
# with the other parameters
if conv is _NoneType and param.kind != param.VAR_POSITIONAL:
ctx.view.undo()
return None if param.default is param.empty else param.default
try:
value = await self._actual_conversion(ctx, conv, argument, param)
except CommandError as e:
@ -317,10 +325,12 @@ class Command:
raise MissingRequiredArgument(param)
return param.default
previous = view.index
if consume_rest_is_special:
argument = view.read_rest().strip()
else:
argument = quoted_word(view)
view.previous = previous
return (await self.do_conversion(ctx, converter, argument, param))