Empty set literal

Question

empty list       empty tuple       empty dict  Is there a similar notation for an empty set  Or do I have to write set

User · Accepted Answer

No  there s no literal syntax for the empty set  You have to write set

User · Answer

Yes  The same notation that works for non-empty dict set works for empty ones  Notice the difference between non-empty dict and set literals   1   a   2   b   3   c   -- a number of key-value pairs inside makes a dict   aaa    bbb    ccc   -- a tuple of values inside makes a set So        zero number of key-value pairs    empty dict          empty tuple of values    empty set However the fact  that you can do it  doesn t mean you should  Unless you have some strong reasons  it s better to construct an empty set explicitly  like  a   set     Performance  The literal is  15  faster than the set-constructor  CPython-3 8  2019 PC  Intel R  Core TM  i7-8550U CPU   1 80GHz    gt  gt  gt   timeit         amp                 214 ns    1 26 ns per loop  mean    std  dev  of 7 runs  1000000 loops each    gt  gt  gt   timeit  set    amp  set      set   252 ns    0 566 ns per loop  mean    std  dev  of 7 runs  1000000 loops each       and for completeness  Renato Garcia s frozenset proposal on the above expression is some 60  faster   gt  gt  gt      frozenset     gt  gt  gt   timeit     amp         100 ns    0 51 ns per loop  mean    std  dev  of 7 runs  10000000 loops each    NB  As ctrueden noticed in comments       is not an empty set  It s a set with 1 element  empty tuple

User · Answer

There are few ways to create empty Set in Python     Using set   method  This is the built-in method in python that creates Empty set in that variable  Using clear   method  creative Engineer Technique LOL   See this Example   sets   Hi   How   are   You   All   type sets  nbsp   This Line  Output   set  sets clear   print sets   nbsp  This Line Output       type sets  nbsp   This Line  Output   set    So  This are 2 ways to create empty Set

User · Answer

Just to extend the accepted answer  From version 2 7 and 3 1 python has got set literal    in form of usage  1 2 3   but    itself still used for empty dict  Python 2 7  first line is invalid in Python  lt 2 7   gt  gt  gt   1 2 3    class    lt type  set  gt   gt  gt  gt       class    lt type  dict  gt   Python 3 x  gt  gt  gt   1 2 3    class    lt class  set  gt   gt  gt  gt       class    lt class  dict  gt   More here  https   docs python org 3 whatsnew 2 7 html other-language-changes

User · Answer

Adding to the crazy ideas  with Python 3 accepting unicode identifiers  you could declare a variable     frozenset      is U 03D5  and use it instead

User · Answer

By all means  please use set   to create an empty set    But  if you want to impress people  tell them that you can create an empty set using literals and   with Python    3 5  see PEP 448  by doing    gt  gt  gt  s            or       or        gt  gt  gt  print s  set     this is basically a more condensed way of doing    for   in      but  don t do this

User · Answer

It depends on if you want the literal for a comparison  or for assignment   If you want to make an existing set empty  you can use the  clear   metod  especially if you want to avoid creating a new object   If you want to do a comparison  use set   or check if the length is 0   example    create a new set     a set  1 2 3  foo   bar     or  using a literal  a  1 2 3  foo   bar     create an empty set a set    or  use the clear method a clear     comparison to a new blank set if a  set         do something   length-checking comparison if len a   0       do something

[python] Empty set literal?

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