A basic dictionary question

[MRAB]

On 2015-06-11 11:10, David Aldrich wrote:
> Hi
>
> I am fairly new to Python.  I am writing some code that uses a
> dictionary to store definitions of hardware registers.  Here is a small
> part of it:
>
> import sys
>
> register = {
>
>      'address'  : 0x3001c,
>
>      'fields' : {
>
>          'FieldA' : {
>
>              'range' : (31,20),
>
>          },
>
>          'FieldB' : {
>
>              'range' : (19,16),
>
>          },
>
>      },
>
>      'width' : 32
>
> };
>
> def main():
>
>      fields = register['fields']
>
>      for field, range_dir in fields:         <== This line fails
>
>          range_dir = field['range']
>
>          x,y = range_dir['range']
>
>          print(x, y)
>
> if __name__ == '__main__':
>
>      main()
>
> I want the code to print the range of bits of each field defined in the
> dictionary.
>
> The output is:
>
> Traceback (most recent call last):
>
>    File "testdir.py", line 32, in <module>
>
>      main()
>
>    File "testdir.py", line 26, in main
>
>      for field, range_dir in fields:
>
> ValueError: too many values to unpack (expected 2)
>
> Please will someone explain what I am doing wrong?
>
You're iterating over the keys. What you want is to iterate over
"fields.items()" which gives the key/value pairs.

> Also I would like to ask how I could print the ranges in the order they
> are defined.  Should I use a different dictionary class or could I add a
> field to the dictionary/list to achieve this?
>
Dicts are unordered. Try 'OrderedDict' from the 'collections' module.