Accessing dict keys element by index in Python3

Question

I m trying to access a dict key s element by its index   test     foo    bar    hello    world   keys   test keys      dict keys object  keys index 0  AttributeError   dict keys  object has no attribute  index    I want to get foo   same with   keys 0  TypeError   dict keys  object does not support indexing   How can I do this

User · Answer

In many cases  this may be an XY Problem   Why are you indexing your dictionary keys by position   Do you really need to   Until recently  dictionaries were not even ordered in Python  so accessing the first element was arbitrary   I just translated some Python 2 code to Python 3   keys   d keys   for  i  res  in enumerate some list       k   keys i              which is not pretty  but not very bad either   At first  I was about to replace it by the monstrous      k   next itertools islice iter keys   i  None     before I realised this is all much better written as  for  k  res  in zip d keys    some list     which works just fine   I believe that in many other cases  indexing dictionary keys by position can be avoided   Although dictionaries are ordered in Python 3 7  relying on that is not pretty   The code above only works because the contents of some list had been recently produced from the contents of d    Have a hard look at your code if you really need to access a disk keys element by index   Perhaps you don t need to

User · Answer

Not a full answer but perhaps a useful hint  If it is really the first item you want   then   next iter q     is much faster than   list q  0    for large dicts  since the whole thing doesn t have to be stored in memory   For 10 000 000 items I found it to be almost 40 000 times faster    The first item in case of a dict being just a pseudo-random item before Python 3 6  after that it s ordered in the standard implementation  although it s not advised to rely on it

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test     foo    bar    hello    world   ls      for key in test keys        ls append key  print ls 0     Conventional way of appending the keys to a statically defined list and then indexing it for same

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Call list   on the dictionary instead   keys   list test    In Python 3  the dict keys   method returns a dictionary view object  which acts as a set  Iterating over the dictionary directly also yields keys  so turning a dictionary into a list results in a list of all the keys    gt  gt  gt  test     foo    bar    hello    world    gt  gt  gt  list test    foo    hello    gt  gt  gt  list test  0   foo

User · Answer

Try this  keys    next iter x keys     for x in test  print list keys     The result looks like this    foo    hello    You can find more possible solutions here

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I wanted  key   amp   value  pair of a first dictionary item  I used the following code    key  val   next iter my dict items

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Python 3 mydict     a    one    b    two    c    three   mykeys     mydict            list of keys myvals     mydict values     list of values  print mykeys  print myvals   Output   a    b    c     one    two    three    Also see this detailed answer

[python] Accessing dict_keys element by index in Python3

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