Further adventures in array slicing.

[Steven W. Orr]

This is more for my education and not so much for practicality.

I have a structure that sort of looks like this:

mdict = {33:{'name': 'Hello0',
             'fields':'fields0',
             'valid': 'valid0'
          55:{'name': 'Hello1',
             'fields':'fields1',
             'valid': 'valid1'},
          14:{'name': 'Hello2',
             'fields':'fields2',
             'valid': 'valid2'}}

i.e, each element of the dictionary is itself a dictionary with three 
common keys.

I need to unpack this into three seperate arrays called name, fields, 
valid. The old code looked like this:

names = []; fields = []; valid = []
for ii in mdict:
     names.append(mdict[ii]['name'])
     fields.append(mdict[ii]['fields'])
     valid.append(mdict[ii]['valid'])

I tried this (to see if it would work) and it seems to work just fine:

def u2(m):
     aa = [ms[ii][jj] for jj in 'name','fields','valid' for ii in m]
     return tuple(zip(aa[0::3], aa[1::3], aa[2::3]))
names,fields,valid = u2(mdict)

I was very pleased with myself, except that the real world example of 
'fields' and 'valid' is that they can be (but not always) a sequence. 
e.g.,

mdefs = {0:{'name': 'Hello0',
             'fields':(('Address', 8),
                         ('Control', 8)),
             'valid': {'Address': (1,255),
                        'Control': (33,44)}},
          1:{'name': 'Hello1',
             'fields':'fields1',
             'valid': 'valid1'},
          2:{'name': 'Hello2',
             'fields':'fields2',
             'valid': 'valid2'}}

Is there a way to do this with possibly a more concise technique than the 
first for loop above?

A second question is: When can you use += vs .append(). Are the two always 
the same?

Thanks. :-)

-- 
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steveo at syslang.net