Returning boolean if set is empty

Question

I am struggling to find a more clean way of returning a boolean value if my set is empty at the end of my function  I take the intersection of two sets  and want to return True or False based on if the resulting set is empty   def myfunc a b       c   a intersection b          return boolean here   My initial thought was to do  return c is not None   However  in my interpreter I can easily see that statement will return true if c   set       gt  gt  gt  c   set      gt  gt  gt  c is not None True   I ve also tried all of the following    gt  gt  gt  c    None False  gt  gt  gt  c    False False  gt  gt  gt  c is None False   Now I ve read from the documentation that I can only use and  or  and not with empty sets to deduce a boolean value  So far  the only thing I can come up with is returning not not c   gt  gt  gt  not not c False  gt  gt  gt  not c True   I have a feeling there is a much more pythonic way to do this  by I am struggling to find it  I don t want to return the actual set to an if statement because I don t need the values  I just want to know if they intersect

User · Answer

If c is a set then you can check whether it s empty by doing  return not c   If c is empty then not c will be True   Otherwise  if c contains any elements not c will be False

User · Answer

def myfunc a b       c   a intersection b      return bool c    bool   will do something similar to not not  but more ideomatic and clear

User · Answer

This function check if set is empty or not   gt  gt  gt  c   set      gt  gt  gt  set is empty c  True   param some set  set to check if he empty or not   return True if empty  False otherwise      def set is empty some set       return some set    set

User · Answer

When you say   c is not None   You are actually checking if c and None reference the same object  That is what the  is  operator does  In python None is a special null value conventionally meaning you don t have a value available  Sorta like null in c or java  Since python internally only assigns one None value using the  is  operator to check if something is None  think null  works  and it has become the popular style  However this does not have to do with the truth value of the set c  it is checking that c actually is a set rather than a null value   If you want to check if a set is empty in a conditional statement  it is cast as a boolean in context so you can just say   c   set   if c     print  it has stuff in it  else     print  it is empty    But if you want it converted to a boolean to be stored away you can simply say   c   set   c has stuff in it   bool c

User · Answer

If you want to return True for an empty set  then I think it would be clearer to do   return c    set     i e   c is equal to an empty set      Or  for the other way around  return c    set      In my opinion  this is more explicit  though less idiomatic  than relying on Python s interpretation of an empty set as False in a boolean context

User · Answer

Not as clean as bool c  but it was an excuse to use ternary   def myfunc a b       return True if a intersection b  else False   Also using a bit of the same logic there is no need to assign to c unless you are using it for something else   def myfunc a b       return bool a intersection b     Finally  I would assume you want a True   False value because you are going to perform some sort of boolean test with it  I would recommend skipping the overhead of a function call and definition by simply testing where you need it   Instead of   if  myfunc a b          Do something   Maybe this   if a intersection b         Do something

User · Answer

not as pythonic as the other answers  but mathematics    return len c     0     As some comments wondered about the impact len set  could have on complexity  It is O 1  as shown in the source code given it relies on a variable that tracks the usage of the set   static Py ssize t set len PyObject  so        return   PySetObject   so - gt used

[python] Returning boolean if set is empty

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