Dictionaries or Associative Arrays in Python

I have a couple previous articles around a similar topic but since I have not added any python code here is a short how to for future reference. It may be called associative arrays in other languages but Python calls it dicts or dictionaries.

Related links:

Creating a javascript array with one to many type relationship

Multi-Array in Bash

Multidimensional array in python

Manually constructing the dictionary:

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mailLists = {}
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mailLists['dba'] = ['joe', 'jim', 'jeff', 'john']
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mailLists['sa'] = ['mike', 'matt' ]
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#print mailLists
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#for key in mailLists:
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#  print key
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print mailLists['dba']
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print mailLists['sa']
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for k,v in mailLists.iteritems():
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  print k + ": " + str(v)

For me the real value in this is for example when you build the lists. Think looping through an input file with lines like this:
jon : dba

Now you add jon to the array with key “dba”. If the key does not exist we simply add one. If the key exists a new item is added to it.

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mailLists = {}
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with open('b.txt') as input_file:
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  for i, line in enumerate(input_file):
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    #print line,
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    v,k = line.strip().split(':')
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    k = k.strip()
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    if k not in mailLists.keys():
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      mailLists[k] = []
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    mailLists[k].append(v)
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for k,v in mailLists.iteritems():
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  print k + ": " + str(v)

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# python b.py
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dba: ['jon ', 'jeff ']
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sa: ['matt ']