How does compare work if value1 == value2 is not None in python?












1














I have found that 



a == b is not None


compared a == b and if it is True than executed b is not None. 



(a == b) is not None


and



a == (b is not None)


Where can I find more information about such behavior?
It is quite simple, but I expected True is not None to be executed






python logical-operators







share|improve this question






















  • 6.16 Operator Precedence
    – DOOM
    Dec 28 '18 at 9:48


















1














I have found that 



a == b is not None


compared a == b and if it is True than executed b is not None. 



(a == b) is not None


and



a == (b is not None)


Where can I find more information about such behavior?
It is quite simple, but I expected True is not None to be executed






python logical-operators







share|improve this question






















  • 6.16 Operator Precedence
    – DOOM
    Dec 28 '18 at 9:48
















1












1








1







I have found that 



a == b is not None


compared a == b and if it is True than executed b is not None. 



(a == b) is not None


and



a == (b is not None)


Where can I find more information about such behavior?
It is quite simple, but I expected True is not None to be executed






python logical-operators







share|improve this question













I have found that 



a == b is not None


compared a == b and if it is True than executed b is not None. 



(a == b) is not None


and



a == (b is not None)


Where can I find more information about such behavior?
It is quite simple, but I expected True is not None to be executed






python logical-operators




python logical-operators






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked Dec 28 '18 at 9:45









Ruslan GalimovRuslan Galimov

1378




1378












  • 6.16 Operator Precedence
    – DOOM
    Dec 28 '18 at 9:48




















  • 6.16 Operator Precedence
    – DOOM
    Dec 28 '18 at 9:48


















6.16 Operator Precedence
– DOOM
Dec 28 '18 at 9:48






6.16 Operator Precedence
– DOOM
Dec 28 '18 at 9:48














1 Answer
1






active

oldest

votes


















2














This is documented in the language reference, 6.10. Comparisons:




Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:



comparison    ::=  or_expr (comp_operator or_expr)*

comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="

                   | "is" ["not"] | ["not"] "in"


Comparisons yield boolean values: True or False.



Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).



Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.



Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).




Both == and is not are comparison operators, so they chain as described above.






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    1 Answer
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    1 Answer
    1






    active

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    active

    oldest

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    active

    oldest

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    2














    This is documented in the language reference, 6.10. Comparisons:




    Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:



    comparison    ::=  or_expr (comp_operator or_expr)*
    
comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="
    
                   | "is" ["not"] | ["not"] "in"


    Comparisons yield boolean values: True or False.



    Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).



    Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.



    Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).




    Both == and is not are comparison operators, so they chain as described above.






    share|improve this answer


























      2














      This is documented in the language reference, 6.10. Comparisons:




      Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:



      comparison    ::=  or_expr (comp_operator or_expr)*
      
comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="
      
                   | "is" ["not"] | ["not"] "in"


      Comparisons yield boolean values: True or False.



      Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).



      Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.



      Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).




      Both == and is not are comparison operators, so they chain as described above.






      share|improve this answer
























        2












        2








        2






        This is documented in the language reference, 6.10. Comparisons:




        Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:



        comparison    ::=  or_expr (comp_operator or_expr)*
        
comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="
        
                   | "is" ["not"] | ["not"] "in"


        Comparisons yield boolean values: True or False.



        Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).



        Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.



        Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).




        Both == and is not are comparison operators, so they chain as described above.






        share|improve this answer












        This is documented in the language reference, 6.10. Comparisons:




        Unlike C, all comparison operations in Python have the same priority, which is lower than that of any arithmetic, shifting or bitwise operation. Also unlike C, expressions like a < b < c have the interpretation that is conventional in mathematics:



        comparison    ::=  or_expr (comp_operator or_expr)*
        
comp_operator ::=  "<" | ">" | "==" | ">=" | "<=" | "!="
        
                   | "is" ["not"] | ["not"] "in"


        Comparisons yield boolean values: True or False.



        Comparisons can be chained arbitrarily, e.g., x < y <= z is equivalent to x < y and y <= z, except that y is evaluated only once (but in both cases z is not evaluated at all when x < y is found to be false).



        Formally, if a, b, c, …, y, z are expressions and op1, op2, …, opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.



        Note that a op1 b op2 c doesn’t imply any kind of comparison between a and c, so that, e.g., x < y > z is perfectly legal (though perhaps not pretty).




        Both == and is not are comparison operators, so they chain as described above.







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered Dec 28 '18 at 9:49









        melpomenemelpomene

        58.9k54489




        58.9k54489






























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