Problems pickling SICDType objects about sarpy HOT 1 CLOSED

Hi, thanks for your message. Just to be clear, how old was the previous version that you were using? I refactored almost everything before about Mar 2020, to make it all more robust. I tried to do it in a way that was transparent to "standard" usage, but there are substantial differences.

To directly answer your question - the various components for the sicd object use the descriptor pattern for all the attributes. Descriptors are sort of indirect properties, and they preclude a few things. You definitely can't use the copy module to make a copy (there is a copy() method of the sicd object). It wouldn't surprise me that pickling doesn't work, and that may be the reason why.

I would suggest that you don't use pickle, which is kind of fragile anyways - you can't use it across different Python versions, for instance. I'd suggest serializing to either json (using the to_dict() method of the sicd object) or xml (using the to_xml_bytes() method of the sicd object).

To reconstruct from json, you use the from_dict class method. Reconstructing from xml is a bit more annoying, because of xml junk - see here https://github.com/ngageoint/sarpy/blob/master/sarpy/io/complex/sicd.py#L158. You parse the xml to etree structure using a method, then pass the etree node info to a from_node class method.

There is documentation on readthedocs - see here for the main sicd object.

Using xml is probably generally preferable - it includes the urn/version information and is generally used, whereas the json is a sarpy only serialization of the SICD structure. The SICD standard uses xml particular structures (like xml attributes), so it's not really xml/json agnostic.

I'll verify that pickling doesn't work, although your code fairly clearly shows that it doesn't. After I verify this, I'll insert a warning in the README - about copy not working either. Please let me know if you need anything else. For questions, feel free to email me at [email protected] or [email protected].

from sarpy.