Access an arbitrary element in a dictionary in Python

Question

If a mydict is not empty  I access an arbitrary element as   mydict mydict keys   0     Is there any better way to do this

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Subclassing dict is one method  though not efficient  Here if you supply an integer it will return d list d  n    otherwise access the dictionary as expected   class mydict dict       def   getitem   self  value           if isinstance value  int               return self get list self  value           else              return self get value   d   mydict   a    hello    b    this    c    is    d    a                e    test    f    dictionary    g    testing     d 0        hello  d 1        this  d  c       is

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Ignoring issues surrounding dict ordering  this might be better   next dict itervalues      This way we avoid item lookup and generating a list of keys that we don t use   Python3  next iter dict values

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No external libraries  works on both Python 2 7 and 3 x    gt  gt  gt  list set   a  1   b   2  values     0  1   For aribtrary key just leave out  values     gt  gt  gt  list set   a  1   b   2    0   a

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As others mentioned  there is no  first item   since dictionaries have no guaranteed order  they re implemented as hash tables    If you want  for example  the value corresponding to the smallest key  thedict min thedict   will do that   If you care about the order in which the keys were inserted  i e   by  first  you mean  inserted earliest   then in Python 3 1 you can use collections OrderedDict  which is also in the forthcoming Python 2 7  for older versions of Python  download  install  and use the ordered dict backport  2 4 and later  which you can find here   Python 3 7 Now dicts are insertion ordered

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In python3  The way    dict keys      return a value in type   dict keys    we ll got an error when got 1st member of keys of dict by this way   dict keys   0  TypeError   dict keys  object does not support indexing   Finally  I convert dict keys   to list  1st  and got 1st member by list splice method   list dict keys    0

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first key   rest keys   mydict

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You can always do   for k in sorted d keys         print d k    This will give you a consistently sorted  with respect to builtin hash   I guess  set of keys you can process on if the sorting has any meaning to you  That means for example numeric types are sorted consistently even if you expand the dictionary   EXAMPLE    lets create a simple dictionary d    1 1  2 2  3 3  4 4  10 10  100 100  print d keys   print sorted d keys       add some other stuff d  peter      peter  d  parker      parker  print d keys   print sorted d keys       some more stuff  numeric of different type  this will  mess up  the keys set order d 0 001    0 001 d 3 14     pie  d 2 71     apple pie  print d keys   print sorted d keys      Note that the dictionary is sorted when printed  But the key set is essentially a hashmap

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If you only need to access one element  being the first by chance  since dicts do not guarantee ordering  you can simply do this in Python 2   my dict keys   0      - gt  key of  first  element my dict values   0    - gt  value of  first  element my dict items   0     - gt   key  value  tuple of  first  element   Please note that  at best of my knowledge  Python does not guarantee that 2 successive calls to any of these methods will return list with the same ordering  This is not supported with Python3   in Python 3   list my dict keys    0      - gt  key of  first  element list my dict values    0    - gt  value of  first  element list my dict items    0     - gt   key  value  tuple of  first  element

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How about  this  Not mentioned here yet   py 2  amp  3  a     a  2  b  3  a list a  0     the first element is here  gt  gt  gt  2

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For both Python 2 and 3   import six  six next six itervalues d

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In python3   list dict values    0

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to get a key  next iter mydict     to get a value  next iter mydict values       to get both  next iter mydict items       or next iter mydict viewitems     in python 2   The first two are Python 2 and 3  The last two are lazy in Python 3  but not in Python 2

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On Python 3  non-destructively and iteratively   next iter mydict values       On Python 2  non-destructively and iteratively   mydict itervalues   next     If you want it to work in both Python 2 and 3  you can use the six package   six next six itervalues mydict     though at this point it is quite cryptic and I d rather prefer your code   If you want to remove any item  do   key  value   mydict popitem     Note that  first  may not be an appropriate term here because dict is not an ordered type in Python  lt  3 6  Python 3 6  dicts are ordered

[python] Access an arbitrary element in a dictionary in Python

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