Want to reduce steps of an operation with dictionaries

Steve Holden steve at holdenweb.com
Wed Oct 25 03:02:59 CEST 2006


pretoriano_2001 at hotmail.com wrote:
> Hello:
> I have next dictionaries:
> a={'a':0, 'b':1, 'c':2, 'd':3}
> b={'a':0, 'c':1, 'd':2, 'e':3}
> I want to put in a new dictionary named c all the keys that are in b
> and re-sequence the values. The result I want is:
> c={'a':0, 'c':1, 'd':2}
> How can I do this with one line of instruction?
> 
You can't. Dictionaries aren't ordered collections.

> I attempted the next but the output is not the expected:
> c=dict([(k,v) for v,k in enumerate(a) if b.has_key(k)])
> erroneously (for me) gets:
> {'a': 0, 'c': 2, 'd': 3}
> 
> Thanks for your help.
> 
In Python {'a':0, 'c':1, 'd':2} == {'a': 0, 'c': 2, 'd': 3}

Sounds like you want an ordered dictionary. Several people have 
implemented such a beast, but I have never felt the need for one.

Alternatively, perhaps the ordering of the elements isn't really important.

regards
  Steve
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