if

syntax: "form":

if boolean_expression:          No "then".
    stmt(s)		     the "body" or "block" of the if.  Must be indented.

semantics: "meaning"/behaviour:
Evaluate the boolean expression, if it's True execute the statements of the body (otherwise skip the body, i.e. when the expression is False).

use:
execute a set of code (the body) if some condition is met (is True). Don't execute the set of code if the condition is False.

The expression is a condition of some sort. A question that is true or false.

  
Relational operators in Python:
<		
>
<=  less than or equal (no ≤ key on keyboard)
>=  greater than or equal
==  equality   Single = is assignment operator.  Don't confuse them!
!=     not equals

An expression with a relational operator evaluates to True or False:

 a  <  b	this expression's value is True or False.

Every expression will have a single value of a particular type when evaluated.


if gpa > 3.5:
    print("Dean's list")

-------------------
if y != 0:		#divide by y only if not zero
    x = 1 / y

-------------------
if y != 0: 		
    x = 1 / y   	#indent all statements of the body
    print("Reciprocal is:", x)

if else

if boolean_expression:
  stmt(s)
else:		#if the expression is not True, 
                 # execute the statements of the else part.
  stmt(s)	# in an if else, either the if body or 
                # the else body will be executed, one
		# or the other but not both