A dictionary (also sometimes called an associative array) is a mapping from 'hashable' objects (e.g., strings, numbers, and tuples of such; see the Python documentation http://docs.python.org/tut/node7.htmland http://docs.python.org/lib/typesmapping.html for details) to arbitrary objects.
sage: d = {1:5, 'sage':17, ZZ:GF(7)} sage: type(d) <type 'dict'> sage: d.keys() [1, 'sage', Integer Ring] sage: d['sage'] 17 sage: d[ZZ] Finite Field of size 7 sage: d[1] 5
The third key illustrates that the indexes of a dictionary can be complicated, e.g., the ring of integers.
You can turn the above dictionary into a list with the same data:
sage: d.items() [(1, 5), ('sage', 17), (Integer Ring, Finite Field of size 7)]
sage: d = {2:4, 3:9, 4:16} sage: [a*b for a, b in d.iteritems()] [8, 27, 64]
A dictionary is unordered, as the last output illustrates.
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