python dictionary using defaultdict(list)

Question

I am using collections.defaultdict(list).

My print looks like the following:

{ 'A': [{'UNP': 'P01899'}],
  'C': [{'PDB': '2VE6'}], 
  'B': [{'PDB': '2VE6'}, {'UNP': 'P01887'}], 
  'E': [{'PDB': '2VE6'}, {'UNP': 'P01887'}],
  'D': [{'UNP': 'P01899'}],
  'G': [{'UNP': 'P01899'}],
  'F': [{'PDB': '2VE6'}], 
  'I': [{'PDB': '2VE6'}],
  'H': [{'PDB': '2VE6'}, {'UNP': 'P01887'}],
  'K': [{'PDB': '2VE6'}, {'UNP': 'P01887'}],
  'J': [{'UNP': 'P01899'}], 
  'L': [{'PDB': '2VE6'}] }

What I want to do is use a clause if 'UNP' do something, if only 'PDB' and no 'UNP' then do something different.

I am very new to scripting. so any help is highly appreciated. thanks

It looks to me that you should be using a dict of dicts, not a dict of list of dicts. — Felix Kling
– Felix Kling, Commented Sep 30, 2012 at 20:57
Your question is difficult to understand. Do you mean you want to process the structure you have somehow? If you just want to use it, it doesn't matter where it came from, so it doesn't matter whether you created it with defaultdict or not. In any case you need to give an example of what you want to do, with code or at least pseudocode. — BrenBarn
– BrenBarn, Commented Sep 30, 2012 at 21:04
Why do you need a collections.defaultdict(list)? Do you want an empty list to be the default value for dictionary entries that are not set explicitly? — Pedro Romano
– Pedro Romano, Commented Sep 30, 2012 at 21:04

Joran Beasley · Accepted Answer · 2012-09-30 22:57:18Z

1

one way is

>>> for key,val in my_dict.items():
...     keys = [v.keys()[0] for v in val]
...     if "UNP" in keys: print "UNP in",key
...     elif "PDB" in keys: print "PDB in",key
...
UNP in A
PDB in C
UNP in B
UNP in E
UNP in D
UNP in G
PDB in F
PDB in I
UNP in H
UNP in K
UNP in J
PDB in L
>>>

edited Sep 30, 2012 at 22:57

answered Sep 30, 2012 at 21:24

Joran Beasley

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Antti Haapala · Accepted Answer · 2012-09-30 22:54:23Z

If each item can have only up to 1 "UNP" and only up to 1 "PDB", you should use defaultdict(dict) in the beginning. Then you can do insertions like this:

mydict['A']['UNP'] = 'P01899'

And get automatically and easily a datastructure like

{ 'A': {'UNP': 'P01899'},
  'C': {'PDB': '2VE6'}, 
  'B': {'PDB': '2VE6', 'UNP': 'P01887'}, 
  'E': {'PDB': '2VE6', 'UNP': 'P01887'},
  'D': {'UNP': 'P01899'},
  'G': {'UNP': 'P01899'},
  'F': {'PDB': '2VE6'}, 
  'I': {'PDB': '2VE6'},
  'H': {'PDB': '2VE6', 'UNP': 'P01887'},
  'K': {'PDB': '2VE6', 'UNP': 'P01887'},
  'J': {'UNP': 'P01899'}, 
  'L': {'PDB': '2VE6'} }

Then what you want is quite straightforward:

itemA = mydict['A']
if 'UNP' in itemA:
    # now we have 'UNP'
elif 'PDB' in itemA:
    # now we have PDB but not UNP

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