python - creating an sql condition object with overloading operators

Question

I am writing a wrapper for SQL Conditions ( so that I can use them in my where statement that I also have a wrapper for ).

Idea is that all of them would be valid :

>> condition_a = Condition("x","=","5")
>> condition_b = Condition("y",">","6")
>> c = condition_a & condition_b
which should give me " x = 5 AND y > 6 "

that is fine so far - I can do so by overloading and, and or.

I don't know what I should overload to have ( working like this ?

>> condition_a = Condition("x","=","5")
>> condition_b = Condition("y",">","6")
>> condition_c = Condition("z",">","7")
>> d = condition_c & ( condition_a |  condition_b )
which should give me " z > 7 AND ( x = 5 OR y > 6 ) "

Sceleton for my condition class is :

class Condition( object ) :
    def __init__( self , args ) :
        ....

    def __and__( self , other ) :
      ...

    def __or__( self , other ) : 
       ...

How can i do that?

Not really a duplicate, but take a look at stackoverflow.com/questions/15719172/… — Bahrom
– Bahrom, Commented Nov 9, 2017 at 16:29
IMO condition_a | condition_b should result in a new ConditionGroup like object as an operand to following computation. — georgexsh
– georgexsh, Commented Nov 9, 2017 at 16:58
@georgexsh can you give an example because I think I am having this problem atm — ghostrider
– ghostrider, Commented Nov 9, 2017 at 17:06

georgexsh · Accepted Answer · 2017-11-13 16:50:46Z

You don't need to overload (, and you can not do that.

As you are generating SQL statements, I guess extra parentheses is acceptable, and less error prone:

class Condition( object ) :
    def __init__( self , *args ) :
        self.args = args

    def __str__(self):
        return '({})'.format(' '.join(map(str, self.args)))

    def __and__( self , other ) :
        return Condition(self, 'and', other)

    def __or__( self , other ) :
        return Condition(self, 'or', other)

condition_a = Condition("x","=","5")
condition_b = Condition("y",">","6")
condition_c = Condition("z",">","7")
d = condition_c & ( condition_a |  condition_b )
print(d)

yields:

((z > 7) and ((x = 5) or (y > 6)))

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