Should I use has key or in on Python dicts

Question

I wonder what is better to do   d     a   1   b   2   a  in d True   or   d     a   1   b   2  d has key  a   True

User · Answer

If you have something like this   t has key ew    change it to below for running on Python 3 X and above   key   ew if key not in t

User · Answer

Expanding on Alex Martelli s performance tests with Adam Parkin s comments       python3 5 -mtimeit -s d dict fromkeys range  99     d has key 12   Traceback  most recent call last     File   usr local Cellar python3 3 5 2 3 Frameworks Python framework Versions 3 5 lib python3 5 timeit py   line 301  in main     x   t timeit number    File   usr local Cellar python3 3 5 2 3 Frameworks Python framework Versions 3 5 lib python3 5 timeit py   line 178  in timeit     timing   self inner it  self timer    File   lt timeit-src gt    line 6  in inner     d has key 12  AttributeError   dict  object has no attribute  has key     python2 7 -mtimeit -s d dict fromkeys range   99     d has key 12   10000000 loops  best of 3  0 0872 usec per loop    python2 7 -mtimeit -s d dict fromkeys range 1999     d has key 12   10000000 loops  best of 3  0 0858 usec per loop    python3 5 -mtimeit -s d dict fromkeys range   99     12 in d  10000000 loops  best of 3  0 031 usec per loop    python3 5 -mtimeit -s d dict fromkeys range 1999     12 in d  10000000 loops  best of 3  0 033 usec per loop    python3 5 -mtimeit -s d dict fromkeys range   99     12 in d keys    10000000 loops  best of 3  0 115 usec per loop    python3 5 -mtimeit -s d dict fromkeys range 1999     12 in d keys    10000000 loops  best of 3  0 117 usec per loop

User · Answer

Solution to dict has key   is deprecated  use  in  -- sublime text editor 3  Here I have taken an example of dictionary named  ages  -  ages         Add a couple of names to the dictionary ages  Sue     23  ages  Peter     19  ages  Andrew     78  ages  Karren     45    use of  in  in if condition instead of function name has key key-name   if  Sue  in ages       print  Sue is in the dictionary  She is   ages  Sue     years old   else       print  Sue is not in the dictionary

User · Answer

in is definitely more pythonic   In fact has key   was removed in Python 3 x

User · Answer

According to python docs      has key   is deprecated in favor of   key in d

User · Answer

Use dict has key   if  and only if  your code is required to be runnable by Python versions earlier than 2 3  when key in dict was introduced

User · Answer

There is one example where in actually kills your performance   If you use in on a O 1  container that only implements   getitem   and has key   but not   contains   you will turn an O 1  search into an O N  search  as in falls back to a linear search via   getitem      Fix is obviously trivial   def   contains   self  x       return self has key x

User · Answer

has key is a dictionary method  but in will work on any collection  and even when   contains   is missing  in will use any other method to iterate the collection to find out

User · Answer

in wins hands-down  not just in elegance  and not being deprecated -  but also in performance  e g      python -mtimeit -s d dict fromkeys range 99     12 in d  10000000 loops  best of 3  0 0983 usec per loop   python -mtimeit -s d dict fromkeys range 99     d has key 12   1000000 loops  best of 3  0 21 usec per loop   While the following observation is not always true  you ll notice that usually  in Python  the faster solution is more elegant and Pythonic  that s why -mtimeit is SO helpful -- it s not just about saving a hundred nanoseconds here and there -

[python] Should I use 'has_key()' or 'in' on Python dicts?

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