CP104: Notes - Boolean Truth Tables

Boolean conditions can be made more powerful with the use of the Boolean operators and, or, and not. These operators act the same way they do in English are are used to either negate (in the case of not) a condition, or allow multiple conditions to be checked within one if or elif.

The operations of these operators are generally represented with truth tables:

not is simple to use - place it outside any condition you wish to negate:

    
if not(x == 0):
    ...

  

Note that conditions on either side of an and or an or must be complete conditions - there are no shortcuts. For example, the following attempt to use an and is incorrect and is a very common error:

    
if x == 5 or 6:
    ...

  

will not cause a Python syntax error - it is a valid Python statement - but it always returns True. Why? Because the value 6 is not actually compared to anything. You are actually asking the separate questions "Is x equal to 5" and "Is 6, 6?", and the answer to second one is, "Yes, 6 is 6."

The correct way to write this clause is:

    
if x == 5 or x == 6:
    ....

  

The variable x is now explicitly compared to both 5 and 6.