How to return dictionary keys as a list in Python

Question

In Python 2 7  I could get dictionary keys  values  or items as a list    gt  gt  gt  newdict    1 0  2 0  3 0   gt  gt  gt  newdict keys    1  2  3    Now  in Python    3 3  I get something like this    gt  gt  gt  newdict keys   dict keys  1  2  3     So  I have to do this to get a list   newlist   list   for i in newdict keys        newlist append i    I m wondering  is there a better way to return a list in Python 3

User · Answer

Converting to a list without using the keys method makes it more readable   list newdict    and  when looping through dictionaries  there s no need for keys     for key in newdict      print key   unless you are modifying it within the loop which would require a list of keys created beforehand   for key in list newdict       del newdict key      On Python 2 there is a marginal performance gain using keys

User · Answer

You can also use a list comprehension    gt  gt  gt  newdict    1 0  2 0  3 0   gt  gt  gt   k  for  k in  newdict keys     1  2  3    Or  shorter    gt  gt  gt   k  for  k in  newdict   1  2  3    Note  Order is not guaranteed on versions under 3 7  ordering is still only an implementation detail with CPython 3 6

User · Answer

I can think of 2 ways in which we can extract the keys from the dictionary   Method 1  - To get the keys using  keys   method and then convert it to list   some dict    1   one   2   two   3   three   list of keys   list some dict keys    print list of keys  -- gt  1 2 3    Method 2  - To create an empty list and then append keys to the list via a loop  You can get the values with this loop as well  use  keys   for just keys and  items   for both keys and values extraction   list of keys      list of values      for key val in some dict items        list of keys append key      list of values append val   print list of keys  -- gt  1 2 3   print list of values  -- gt   one   two   three

User · Answer

If you need to store the keys separately  here s a solution that requires less typing than every other solution presented thus far  using Extended Iterable Unpacking  python3 x      newdict    1  0  2  0  3  0   k    newdict  k    1  2  3                   ---------------------------------------------------------                 k   list d         9 characters  excluding whitespace                    --------------- -----------------------------------------                  k     d            6 characters                                          --------------- -----------------------------------------                   k    d            5 characters                                          ---------------------------------------------------------

User · Answer

Try list newdict keys      This will convert the dict keys object to a list   On the other hand  you should ask yourself whether or not it matters  The Pythonic way to code is to assume duck typing  if it looks like a duck and it quacks like a duck  it s a duck   The dict keys object will act like a list for most purposes  For instance   for key in newdict keys      print key    Obviously  insertion operators may not work  but that doesn t make much sense for a list of dictionary keys anyway

User · Answer

A bit off on the  duck typing  definition -- dict keys   returns an iterable object  not a list-like object  It will work anywhere an iterable will work -- not any place a list will  a list is also an iterable  but an iterable is NOT a list  or sequence      In real use-cases  the most common thing to do with the keys in a dict is to iterate through them  so this makes sense  And if you do need them as a list you can call list      Very similarly for zip   -- in the vast majority of cases  it is iterated through -- why create an entire new list of tuples just to iterate through it and then throw it away again   This is part of a large trend in python to use more iterators  and generators   rather than copies of lists all over the place   dict keys   should work with comprehensions  though -- check carefully for typos or something    it works fine for  me    gt  gt  gt  d   dict zip   Sounder V Depth  F    Vessel Latitude  Degrees-Minutes     None  None     gt  gt  gt   key split       for key in d keys       Sounder V Depth    F      Vessel Latitude    Degrees-Minutes

User · Answer

Python    3 5 alternative  unpack into a list literal   newdict   New unpacking generalizations  PEP 448  were introduced with Python 3 5 allowing you to now easily do    gt  gt  gt  newdict    1 0  2 0  3 0   gt  gt  gt    newdict   1  2  3    Unpacking with   works with any object that is iterable and  since dictionaries return their keys when iterated through  you can easily create a list by using it within a list literal    Adding  keys   i e   newdict keys    might help in making your intent a bit more explicit though it will cost you a function look-up and invocation   which  in all honesty  isn t something you should really be worried about     The  iterable syntax is similar to doing list iterable  and its behaviour was initially documented in the Calls section of the Python Reference manual  With PEP 448 the restriction on where  iterable could appear was loosened allowing it to also be placed in list  set and tuple literals  the reference manual on Expression lists was also updated to state this      Though equivalent to list newdict  with the difference that it s faster  at least for small dictionaries  because no function call is actually performed    timeit   newdict  1000000 loops  best of 3  249 ns per loop   timeit list newdict  1000000 loops  best of 3  508 ns per loop   timeit  k for k in newdict  1000000 loops  best of 3  574 ns per loop   with larger dictionaries the speed is pretty much the same  the overhead of iterating through a large collection trumps the small cost of a function call      In a similar fashion  you can create tuples and sets of dictionary keys    gt  gt  gt   newdict   1  2  3   gt  gt  gt    newdict   1  2  3    beware of the trailing comma in the tuple case

User · Answer

list newdict  works in both Python 2 and Python 3  providing a simple list of the keys in newdict  keys   isn t necessary

[python] How to return dictionary keys as a list in Python?

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