if elif else

If elif else

A notable feature is that the flow of control continues "downward". In the simple if/else flow shown here, is the condition evaluated in the diamond results in a True, the "if branch" is executed.

If the condition evaluated in the diamond results in a False, the "else branch" is executed.

If there were two or more subsequent ifs, then all would get evaluated, i.e.

if test_exp1:

statement 1

if test_exp2:

statement 2

if test_exp2:

statement 3

but only get executed if the expression results in a True

Chained Conditionals

In a sequence of code such as:

if test_exp1:

statement 1

elif test_exp2:

statement 2

elif test_exp2:

statement 3

else:

body_of_else

if the if, or a subsequent elif evaluates to True, then that branch gets executed. If all evaluate to False, then and only then would the else block - if used - get executed.

This allows the use of bounded values: e.g. if checking grades, and the first check is for < 50, if the next check is looking for a grade between 50 and < 65, sequential ifs are much less convenient than an if/elif/else block.

# using if and elif is simpler

if grade < 50:

return "Fail"

elif grade < 65:

return "Merit"

# sequential ifs add some complexity and

# all if statements get tested.

if grade < 50:

return "Fail"

if grade >=50 and grade < 65:

return "Merit"

Ternary Conditional operator

a if condition else b # expression syntax

Think of the conditional expression as switching between two values. It is very useful when you're in a 'one value or another' situation, it but doesn't do much else.

result = "Pass" if grade >= 50 else "Fail"

If you need to use statements, you have to use a normal if statement instead of a conditional expression. If you're having trouble remembering the order, then remember that when read aloud, you (almost) say what you mean.

For example, x = 4 if b > 8 else 9 is read aloud as x will be 4 if b is greater than 8 otherwise 9.

Official documentation:

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