Currently the mmCIF unknown value is represented as a literal ? Python string. This makes it impossible to distinguish from the actual string "?". On the other hand, the omitted value is represented specially (as the Python value None, not as the literal . string) which will never compare equal to any other valid mmCIF value. We should use something similar for mmCIF-unknown.
Note that this would also make handling BinaryCIF more straightforward, since BinaryCIF does not use the values . and ? but instead uses a bitmask.
Currently the mmCIF unknown value is represented as a literal
?Python string. This makes it impossible to distinguish from the actual string "?". On the other hand, the omitted value is represented specially (as the Python valueNone, not as the literal.string) which will never compare equal to any other valid mmCIF value. We should use something similar for mmCIF-unknown.Note that this would also make handling BinaryCIF more straightforward, since BinaryCIF does not use the values
.and?but instead uses a bitmask.