Python Program Control Structures

if Statements
If an expression returns TRUE statements are carried out; otherwise, they aren't.

if expression:
  statements

Sample:

no = 11
  if no >10:
   print ("Greater than 10")
   if no <=30
     printf ("Between 10 and 30")

Output:

>>>
Greater than 10
Between 10 and 30
>>>

else Statements
An else statement follows an if statement and contains code called when the if statement is FALSE.

x = 2
if x == 6
  printf ("Yes")
else:
  printf ("No")  

elif Statements
The elif (shortcut of else if) statement is used when changing if and else statements. A series of if…elif statements can have a final else block, which is called if none of the if or elif expressions is TRUE.

num = 12
if num == 5:
  printf ("Number = 5")
elif num == 4:
  printf ("Number = 4")
elif num == 3:
  printf ("Number = 3")
else:
  printf ("Number = 12")

Output:

>>>
 Number = 12
>>>

Boolean Logic
Python uses logic operators like AND, OR and NOT.

The AND operator uses two arguments and evaluates to TRUE if, and only if, both arguments are TRUE. Otherwise, it evaluates to FALSE.

>>> 1 == 1 and 2 == 2
True
>>> 1 == 1 and 2 == 3
False
>>> 1 != 1 and 2 == 2
False
>>> 4 < 2 and 2 > 6
False
>>>

Boolean operator or uses two arguments and evaluates as TRUE if either (or both) of its arguments are TRUE, and FALSE if both arguments are FALSE.

The result of NOT TRUE is FALSE, and NOT FALSE goes to TRUE.

>>> not 2 == 2
False
>>> not 6 > 10
True
>>>

Operator Precedence
Operator Precedence uses the mathematical idea of operation order, e.g. multiplication begins performed before addition.

>>> False == False or True
True
>>> False == (False or True)
False
>>> (False == False) or True
>>>True
>>>