I mentioned this problem in #2782 but it still occurs in version 1.0.10

@abn approved it's a bug in parsing, see here

Reproducing the problem

When we have space after comma it can't parses the rest of extras.

poetry add databases[postgresql, sqlite]

[ValueError]
Could not find a matching version of package databases[postgresql,

It works perfectly fine without a space.

poetry add databases[postgresql,sqlite]
Using version ^0.3.2 for databases