If you need to evaluate more than one condition to determine whether to execute a block of code, you can use Boolean operators to specify multiple conditions.

The most commonly used Boolean operators are and, or and not.

The and operator specifies that a condition is true only if both of its subconditions are true. For instance:

patientid = 42113
hospitalid = 1000
if patientid == 42113 and hospitalid == 1000:
	print "patientid is 42113 and hospitalid is 1000"

The or operator specifies that a condition is true if either of its subconditions is true:

patientid = 42113
hospitalid = 2000
if patientid == 42113 or hospitalid == 1000:
	print "patientid is 42113 or hospitalid is 1000"

The not operator specifies that a condition is true if its subcondition is false:

patientid = 42113
if not patientid == 42113:
	print "patientid is not 42113"

You can combine Boolean operators to specify more than two subconditions:

patientid = 42113
hospitalid = 1000
labid = 5555
if patientid == 42113 and hospitalid == 1000 and labid == 5555:
	print "patientid is 42113, hospitalid is 1000, and labid is 5555"

If and, or and not operators are contained in a single condition, Python evaluates them in the following order:

• not is evaluated first;
• and is evaluated next;
• or is evaluated last.

To force a subcondition to be evaluated first, enclose it in parentheses:

patientid = 42113
hospitalid = 1000
if not (patientid == 42113 and hospitalid == 2000):
    print "This statement is true"

	Use parentheses whenever the order of evaluation is not obvious. This will prevent confusion later.