How do you find the first key in a dictionary

Question

I am trying to get my program to print out  banana  from the dictionary  What would be the simplest way to do this   This is my dictionary    prices          banana    4       apple    2       orange    1 5       pear    3

User · Answer

The dict type is an unordered mapping  so there is no such thing as a  first  element   What you want is probably collections OrderedDict

User · Answer

Use a for loop that ranges through all keys in prices   for key  value in prices items         print key      print  price   s   value   Make sure that you change prices items   to prices iteritems   if you re using Python 2 x

User · Answer

easiest way is   first key   my dict keys   0    but some times you should be more careful and assure that your entity is a valuable list so    first key   list my dict keys    0

User · Answer

A dictionary is not indexed  but it is in some way  ordered  The following would give you the first existing key   list my dict keys    0

User · Answer

As many others have pointed out there is no first value in a dictionary  The sorting in them is arbitrary and you can t count on the sorting being the same every time you access the dictionary  However if you wanted to print the keys there a couple of ways to it   for key  value in prices items        print key    This method uses tuple assignment to access the key and the value  This handy if you need to access both the key and the value for some reason   for key in prices keys        print key    This will only gives access to the keys as the keys   method implies

User · Answer

If you just want the first key from a dictionary you should use what many have suggested before first   next iter prices    However if you want the first and keep the rest as a list you could use the values unpacking operator first   rest   prices  The same is applicable on values by replacing prices with prices values   and for both key and value you can even use unpacking assignment  gt  gt  gt   product  price    rest   prices items    gt  gt  gt  product  banana   gt  gt  gt  price 4   Note  You might be tempted to use first       prices to just get the first key  but I would generally advice against this usage unless the dictionary is very short since it loops over all keys and creating a list for the rest has some overhead    Note  As mentioned by others insertion order is preserved from python 3 7  or technically 3 6  and above whereas earlier implementations should be regarded as undefined order

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Update  as of Python 3 7  insertion order is maintained  so you don t need an OrderedDict here  You can use the below approaches with a normal dict     Changed in version 3 7  Dictionary order is guaranteed to be insertion order  This behavior was an implementation detail of CPython from 3 6    source    Python 3 6 and earlier   If you are talking about a regular dict  then the  first key  doesn t mean anything  The keys are not ordered in any way you can depend on  If you iterate over your dict you will likely not get  banana  as the first thing you see   If you need to keep things in order  then you have to use an OrderedDict and not just a plain dictionary   import collections prices    collections OrderedDict             banana   4             apple   2             orange   1 5             pear   3        If you then wanted to see all the keys in order you could do so by iterating through it  for k in prices      print k    You could  alternatively put all of the keys into a list and then work with that  ks   list prices  print ks 0     will print  banana    A faster way to get the first element without creating a list would be to call next on the iterator  This doesn t generalize nicely when trying to get the nth element though   gt  gt  gt  next iter prices    banana      CPython had guaranteed insertion order as an implementation detail in 3 6

User · Answer

On a Python version where dicts actually are ordered  you can do  my dict     foo    bar    spam    eggs   next iter my dict     outputs  foo    For dicts to be ordered  you need Python 3 7   or 3 6  if you re okay with relying on the technically-an-implementation-detail ordered nature of dicts on Python 3 6   For earlier Python versions  there is no  first key

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So I found this page while trying to optimize a thing for taking the only key in a dictionary of known length 1 and returning only the key  The below process was the fastest for all dictionaries I tried up to size 700   I tried 7 different approaches  and found that this one was the best  on my 2014 Macbook with Python 3 6   def first 5        for key in biased dict          return key   The results of profiling them were     2226460   s with first 1   1905620   s with first 2   1994654   s with first 3   1777946   s with first 4   3681252   s with first 5   2829067   s with first 6   2600622   s with first 7   All the approaches I tried are here   def first 1        return next iter biased dict     def first 2        return list biased dict  0    def first 3        return next iter biased dict keys       def first 4        return list biased dict keys    0    def first 5        for key in biased dict          return key   def first 6        for key in biased dict keys            return key   def first 7        for key  v in biased dict items            return key

User · Answer

For Python 3 below eliminates overhead of list conversion   first   next iter prices values

User · Answer

d keys   0  to get the individual key   Update -   AlejoBernardin   am not sure why you said it didn t work  here I checked and it worked  import collections  prices    collections OrderedDict          banana   4         apple   2         orange   1 5         pear   3      prices keys   0             banana

User · Answer

Well as simple  the answer according to me will be  first   list prices  0   converting the dictionary to list will output the keys and we will select the first key from the list

[python] How do you find the first key in a dictionary?

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