CODEWITHSUNDEEP
pythondictionary
RatDon
RatDon

Reputation: 3543

python dictionary assignment not in order

I wanted to use a dictionary both with the keys and also like lists with indexing. but i found that assignment to an dictionary is not in order.

my python script is:

left=['E','Z','T','Y','F']

for lhs in left:
  first[lhs]=set()
  follow[lhs]=set()
  print first

and i get the output as:

{'E': set([])}
{'Z': set([]), 'E': set([])}
{'Z': set([]), 'E': set([]), 'T': set([])}
{'Y': set([]), 'Z': set([]), 'E': set([]), 'T': set([])}
{'Y': set([]), 'Z': set([]), 'E': set([]), 'T': set([]), 'F': set([])}

one time it's inserted at end and another time it's at the beginning. this made me to think that i dont know the dictionary at all. where can i know the dictionary in depth. and how can iterate through a dictionary with keys as well as with indexes. for this i'm using now:

for lhs in left:
  print first[lhs]

this some how helps with indexing. but is there any other method?

Upvotes: 1

Views: 330

Answers (1)

chepner
chepner

Reputation: 531075

Use collections.OrderedDict. It requires Python 2.7, but it remembers the order in which keys are added, rather than storing them in an arbitrary order based on the underlying hash algorithm.

Update: to be precise, the storage of the dict is unchanged, but the iteration is implemented with an additional data structure to provide a fixed order based on the original insertion order of the keys.

Upvotes: 6

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