Why are 'and/or' operations in this Python statement behaving unexpectedly?












5















I have a conceptual question about Python. This is the code



list1=['assistant manager', 'salesperson', 'doctor', 'production manager', 'sales manager', 'schoolteacher', 'mathematics teacher']

sub1 = "teacher"

sub2 = "sales"

ans=



for item in list1:

    if (sub1 and sub2) in item:

        ans.append(item)


Here, I expect the list to be empty as none of the items satisfy the condition if sub1 and sub2 in item: But when I print the list I get the output#1 as this



>>> ans

['salesperson', 'sales manager'] # I expected an empty list here


Also, when I use or instead of and as given below



for item in list1:

    if (sub1 or sub2) in item:

        ans.append(item)


the output#2 I get is



>>> ans

['schoolteacher', 'mathematics teacher'] # I expected a list of words containing sub1 or sub2 as their substrings


I saw a similar looking solution here, but it does not exactly solve my problem. Both the times I get a result which I do not expect while using and and or. Why is this happening during both these operations?






python logical-operators







share|improve this question




















  • 1





    (sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

    – Klaus D.
    18 hours ago













  • Change (sub1 and sub2) in item to sub1 in item and sub2 in item

    – Tom Karzes
    18 hours ago








  • 2





    Possible duplicate of can Python 'and' return None?

    – user5173426
    18 hours ago
















5















I have a conceptual question about Python. This is the code



list1=['assistant manager', 'salesperson', 'doctor', 'production manager', 'sales manager', 'schoolteacher', 'mathematics teacher']

sub1 = "teacher"

sub2 = "sales"

ans=



for item in list1:

    if (sub1 and sub2) in item:

        ans.append(item)


Here, I expect the list to be empty as none of the items satisfy the condition if sub1 and sub2 in item: But when I print the list I get the output#1 as this



>>> ans

['salesperson', 'sales manager'] # I expected an empty list here


Also, when I use or instead of and as given below



for item in list1:

    if (sub1 or sub2) in item:

        ans.append(item)


the output#2 I get is



>>> ans

['schoolteacher', 'mathematics teacher'] # I expected a list of words containing sub1 or sub2 as their substrings


I saw a similar looking solution here, but it does not exactly solve my problem. Both the times I get a result which I do not expect while using and and or. Why is this happening during both these operations?






python logical-operators







share|improve this question




















  • 1





    (sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

    – Klaus D.
    18 hours ago













  • Change (sub1 and sub2) in item to sub1 in item and sub2 in item

    – Tom Karzes
    18 hours ago








  • 2





    Possible duplicate of can Python 'and' return None?

    – user5173426
    18 hours ago














5












5








5


0






I have a conceptual question about Python. This is the code



list1=['assistant manager', 'salesperson', 'doctor', 'production manager', 'sales manager', 'schoolteacher', 'mathematics teacher']

sub1 = "teacher"

sub2 = "sales"

ans=



for item in list1:

    if (sub1 and sub2) in item:

        ans.append(item)


Here, I expect the list to be empty as none of the items satisfy the condition if sub1 and sub2 in item: But when I print the list I get the output#1 as this



>>> ans

['salesperson', 'sales manager'] # I expected an empty list here


Also, when I use or instead of and as given below



for item in list1:

    if (sub1 or sub2) in item:

        ans.append(item)


the output#2 I get is



>>> ans

['schoolteacher', 'mathematics teacher'] # I expected a list of words containing sub1 or sub2 as their substrings


I saw a similar looking solution here, but it does not exactly solve my problem. Both the times I get a result which I do not expect while using and and or. Why is this happening during both these operations?






python logical-operators







share|improve this question
















I have a conceptual question about Python. This is the code



list1=['assistant manager', 'salesperson', 'doctor', 'production manager', 'sales manager', 'schoolteacher', 'mathematics teacher']

sub1 = "teacher"

sub2 = "sales"

ans=



for item in list1:

    if (sub1 and sub2) in item:

        ans.append(item)


Here, I expect the list to be empty as none of the items satisfy the condition if sub1 and sub2 in item: But when I print the list I get the output#1 as this



>>> ans

['salesperson', 'sales manager'] # I expected an empty list here


Also, when I use or instead of and as given below



for item in list1:

    if (sub1 or sub2) in item:

        ans.append(item)


the output#2 I get is



>>> ans

['schoolteacher', 'mathematics teacher'] # I expected a list of words containing sub1 or sub2 as their substrings


I saw a similar looking solution here, but it does not exactly solve my problem. Both the times I get a result which I do not expect while using and and or. Why is this happening during both these operations?






python logical-operators




python logical-operators






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 12 hours ago









Peter Mortensen

13.7k1986112




13.7k1986112










asked 18 hours ago









satyasatya

16812




16812








  • 1





    (sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

    – Klaus D.
    18 hours ago













  • Change (sub1 and sub2) in item to sub1 in item and sub2 in item

    – Tom Karzes
    18 hours ago








  • 2





    Possible duplicate of can Python 'and' return None?

    – user5173426
    18 hours ago














  • 1





    (sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

    – Klaus D.
    18 hours ago













  • Change (sub1 and sub2) in item to sub1 in item and sub2 in item

    – Tom Karzes
    18 hours ago








  • 2





    Possible duplicate of can Python 'and' return None?

    – user5173426
    18 hours ago








1




1





(sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

– Klaus D.
18 hours ago







(sub1 and sub2) in item what will be the result of the expression in the brackets? That will be checked against item.

– Klaus D.
18 hours ago















Change (sub1 and sub2) in item to sub1 in item and sub2 in item

– Tom Karzes
18 hours ago







Change (sub1 and sub2) in item to sub1 in item and sub2 in item

– Tom Karzes
18 hours ago






2




2





Possible duplicate of can Python 'and' return None?

– user5173426
18 hours ago





Possible duplicate of can Python 'and' return None?

– user5173426
18 hours ago












2 Answers
2






active

oldest

votes


















16














("teacher" and "sales") in "salesmanager" do not mean the same in Python and in English.



In English, it is synonynous to ("teacher" in "salesmanager") and ("sales" in "salesmanager") (which Python would understand as you thought it should, and evaluate to False).



Python on the other hand will first evaluate "teacher" and "sales", because it is in parentheses, and thus has higher priority. and will return the first argument if falsy, otherwise the second argument. "teacher" is not falsy, so "teacher" and "sales" evaluates as "sales". Then, Python continues to evaluate "sales" in "salesmanager", and returns True.






share|improve this answer
























  • So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

    – Carl Witthoft
    12 hours ago



















5














The and and or operators don't do what you think they do. Try breaking up your expressions:



if sub1 in item or sub2 in item:



if sub1 in item and sub2 in item:


The and operator evaluates its left-hand operand and, if the result is truthy, returns the right-hand operand, otherwise the left-hand operand.



The or operator evaluates its left-hand operand and, if the result is falsy, returns the right-hand operand, otherwise the left-hand operand.



So, in your first expression evaluates as follows:



(sub1 and sub2) in item

("teacher" and "sales") in item

("sales") in item


which is not what you expected.



Similarly for your second expression:



(sub1 or sub2) in item

("teacher" or "sales") in item

("teacher") in item





share|improve this answer























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    2 Answers
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    2 Answers
    2






    active

    oldest

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    active

    oldest

    votes






    active

    oldest

    votes









    16














    ("teacher" and "sales") in "salesmanager" do not mean the same in Python and in English.



    In English, it is synonynous to ("teacher" in "salesmanager") and ("sales" in "salesmanager") (which Python would understand as you thought it should, and evaluate to False).



    Python on the other hand will first evaluate "teacher" and "sales", because it is in parentheses, and thus has higher priority. and will return the first argument if falsy, otherwise the second argument. "teacher" is not falsy, so "teacher" and "sales" evaluates as "sales". Then, Python continues to evaluate "sales" in "salesmanager", and returns True.






    share|improve this answer
























    • So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

      – Carl Witthoft
      12 hours ago
















    16














    ("teacher" and "sales") in "salesmanager" do not mean the same in Python and in English.



    In English, it is synonynous to ("teacher" in "salesmanager") and ("sales" in "salesmanager") (which Python would understand as you thought it should, and evaluate to False).



    Python on the other hand will first evaluate "teacher" and "sales", because it is in parentheses, and thus has higher priority. and will return the first argument if falsy, otherwise the second argument. "teacher" is not falsy, so "teacher" and "sales" evaluates as "sales". Then, Python continues to evaluate "sales" in "salesmanager", and returns True.






    share|improve this answer
























    • So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

      – Carl Witthoft
      12 hours ago














    16












    16








    16







    ("teacher" and "sales") in "salesmanager" do not mean the same in Python and in English.



    In English, it is synonynous to ("teacher" in "salesmanager") and ("sales" in "salesmanager") (which Python would understand as you thought it should, and evaluate to False).



    Python on the other hand will first evaluate "teacher" and "sales", because it is in parentheses, and thus has higher priority. and will return the first argument if falsy, otherwise the second argument. "teacher" is not falsy, so "teacher" and "sales" evaluates as "sales". Then, Python continues to evaluate "sales" in "salesmanager", and returns True.






    share|improve this answer













    ("teacher" and "sales") in "salesmanager" do not mean the same in Python and in English.



    In English, it is synonynous to ("teacher" in "salesmanager") and ("sales" in "salesmanager") (which Python would understand as you thought it should, and evaluate to False).



    Python on the other hand will first evaluate "teacher" and "sales", because it is in parentheses, and thus has higher priority. and will return the first argument if falsy, otherwise the second argument. "teacher" is not falsy, so "teacher" and "sales" evaluates as "sales". Then, Python continues to evaluate "sales" in "salesmanager", and returns True.







    share|improve this answer












    share|improve this answer



    share|improve this answer










    answered 18 hours ago









    AmadanAmadan

    131k13143196




    131k13143196













    • So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

      – Carl Witthoft
      12 hours ago



















    • So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

      – Carl Witthoft
      12 hours ago

















    So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

    – Carl Witthoft
    12 hours ago





    So far as I know, all languages give parentheses first priority, not just Python. But you are correct in explaining what Python returns for ( X and Y )

    – Carl Witthoft
    12 hours ago













    5














    The and and or operators don't do what you think they do. Try breaking up your expressions:



    if sub1 in item or sub2 in item:
    

    
if sub1 in item and sub2 in item:


    The and operator evaluates its left-hand operand and, if the result is truthy, returns the right-hand operand, otherwise the left-hand operand.



    The or operator evaluates its left-hand operand and, if the result is falsy, returns the right-hand operand, otherwise the left-hand operand.



    So, in your first expression evaluates as follows:



    (sub1 and sub2) in item
    
("teacher" and "sales") in item
    
("sales") in item


    which is not what you expected.



    Similarly for your second expression:



    (sub1 or sub2) in item
    
("teacher" or "sales") in item
    
("teacher") in item





    share|improve this answer




























      5














      The and and or operators don't do what you think they do. Try breaking up your expressions:



      if sub1 in item or sub2 in item:
      

      
if sub1 in item and sub2 in item:


      The and operator evaluates its left-hand operand and, if the result is truthy, returns the right-hand operand, otherwise the left-hand operand.



      The or operator evaluates its left-hand operand and, if the result is falsy, returns the right-hand operand, otherwise the left-hand operand.



      So, in your first expression evaluates as follows:



      (sub1 and sub2) in item
      
("teacher" and "sales") in item
      
("sales") in item


      which is not what you expected.



      Similarly for your second expression:



      (sub1 or sub2) in item
      
("teacher" or "sales") in item
      
("teacher") in item





      share|improve this answer


























        5












        5








        5







        The and and or operators don't do what you think they do. Try breaking up your expressions:



        if sub1 in item or sub2 in item:
        

        
if sub1 in item and sub2 in item:


        The and operator evaluates its left-hand operand and, if the result is truthy, returns the right-hand operand, otherwise the left-hand operand.



        The or operator evaluates its left-hand operand and, if the result is falsy, returns the right-hand operand, otherwise the left-hand operand.



        So, in your first expression evaluates as follows:



        (sub1 and sub2) in item
        
("teacher" and "sales") in item
        
("sales") in item


        which is not what you expected.



        Similarly for your second expression:



        (sub1 or sub2) in item
        
("teacher" or "sales") in item
        
("teacher") in item





        share|improve this answer













        The and and or operators don't do what you think they do. Try breaking up your expressions:



        if sub1 in item or sub2 in item:
        

        
if sub1 in item and sub2 in item:


        The and operator evaluates its left-hand operand and, if the result is truthy, returns the right-hand operand, otherwise the left-hand operand.



        The or operator evaluates its left-hand operand and, if the result is falsy, returns the right-hand operand, otherwise the left-hand operand.



        So, in your first expression evaluates as follows:



        (sub1 and sub2) in item
        
("teacher" and "sales") in item
        
("sales") in item


        which is not what you expected.



        Similarly for your second expression:



        (sub1 or sub2) in item
        
("teacher" or "sales") in item
        
("teacher") in item






        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered 18 hours ago









        RobᵩRobᵩ

        117k13138222




        117k13138222






























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