pydicom show <file>::TransferSyntaxUID

[crossmanith]

How would I call pydicom to print elements from group 0x0002? pydicom show <file>::SOPInstanceUID works as expected, pydicom show <file>::TransferSyntaxUID leads to this error message:
pydicom show: error: argument filespec: Data element 'TransferSyntaxUID' is not in the dataset

[darcymason]

Actually it is possible:

pydicom show <file>::file_meta.TransferSyntaxUID

[mrbean-bremen]

pydicom show <file>::file_meta.TransferSyntaxUID.name should work.

[crossmanith]

Great! Is this secret knowledge or could I get this information from the documentation (I've tried but obviously failed)

[mrbean-bremen]

There is no explicit information, I think, but you could get it from the pydicom documentation if you know the returned value type. For TransferSyntaxUID, the value type is uid.UID, which has properties like name, uid and keyword.

[darcymason]

Great! Is this secret knowledge or could I get this information from the documentation (I've tried but obviously failed)

Access to file_meta is a bit of a gotcha for many new to pydicom - in DICOM files it actually is a separate Dataset and pydicom treats it that way but many libraries just group everything together. It is in the documentation but not in the early user guide pages, maybe it should be there too.

I guess you've seen the pydicom show documentation, in the filespec description of pydicom help show there is a little bit about what can be passed, and then some examples. However, it could definitely benefit from showing a file_meta example.

As it happens, the .name working is just a bit of an accident, because what is allowed is defined by some regex expressions which include any items separated by ., which was really intended to allow one to traverse items within a sequence, as one filespec element example has.

I'll try to put a PR together to add a little to the documentation to show the file_meta example, I think that would be useful to many people.

[scaramallion]

Might be good to automatically warn if group 0x0002 elements are searched for in the base dataset?