deepcopy of subint HDU

[luojing1211]

Since we modified the new of subint HDU class. It will raise error when deepcopying it. Is there a way to make the deepcopy work again?

import copy
>>> f = open('../../Projects/test_data/CHIME_B1937+21_grid01_beam_7_58464_79458.fits', 'r')
>>> type(f.ih)
    scintillometry.io.psrfits.hdu.PSRSubintHDU
>>> copy.deepcopy(f.ih)
---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
~/.local/lib/python3.6/site-packages/scintillometry-0.0.dev374-py3.6.egg/scintillometry/io/psrfits/hdu.py in __new__(cls, hdu, primary_hdu, verify)
    232         try:
--> 233             mode = primary_hdu.obs_mode
    234             cls = subint_map[mode]

AttributeError: 'NoneType' object has no attribute 'obs_mode'

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-12-4531c13cc470> in <module>
----> 1 copy.deepcopy(f.ih)

~/anaconda3/lib/python3.6/copy.py in deepcopy(x, memo, _nil)
    178                     y = x
    179                 else:
--> 180                     y = _reconstruct(x, memo, *rv)
    181 
    182     # If is its own copy, don't memoize.

~/anaconda3/lib/python3.6/copy.py in _reconstruct(x, memo, func, args, state, listiter, dictiter, deepcopy)
    272     if deep and args:
    273         args = (deepcopy(arg, memo) for arg in args)
--> 274     y = func(*args)
    275     if deep:
    276         memo[id(x)] = y

~/anaconda3/lib/python3.6/copyreg.py in __newobj__(cls, *args)
     86 
     87 def __newobj__(cls, *args):
---> 88     return cls.__new__(cls, *args)
     89 
     90 def __newobj_ex__(cls, args, kwargs):

~/.local/lib/python3.6/site-packages/scintillometry-0.0.dev374-py3.6.egg/scintillometry/io/psrfits/hdu.py in __new__(cls, hdu, primary_hdu, verify)
    234             cls = subint_map[mode]
    235         except AttributeError:
--> 236             raise ValueError("need a primary HDU to determine the mode.")
    237         except KeyError:
    238             raise ValueError("'{}' is not a valid mode.".format(mode))

ValueError: need a primary HDU to determine the mode.

[mhvk]

Ah, yes, I had a similar problem while setting up pickling for baseband - mhvk/baseband@9563dca#diff-a3f78791258cf574889e85e114fb8192 - basically ensure that all arguments have defaults and that a non-default argument is only required if the class is actually the one that selects the different cases.