Further adventures in array slicing.

[Alex Martelli]

Steven W. Orr <steveo at syslang.net> wrote:
   ...
> I need to unpack this into three seperate arrays called name, fields,
> valid. The old code looked like this:

You're using lists, not arrays.  If you DID want arrays, you'd have to
import standard library module array, and you'd be limited to a few
elementary types as items; it's pretty obvious that this is not what you
want -- nevertheless, why use the wrong name?

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

The order of keys in dictionary mdict is totally arbitrary, therefore
the order of items in those lists is going to be equally arbitrary; you
sure you _want_ that?  Normally order IS significant in lists.

> 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.

Why would that make any difference at all?

> 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?

not by much:

names = [v['name'] for v in mdict.itervalues()]
fields = [v['fields'] for v in mdict.itervalues()]
valid = [v['valid'] for v in mdict.itervalues()]

but this just saves a few characters, if that.


Alex