When we write the code in any language, we always write portion of the code to execute depending on certain condition(s). This will give more control and easy to manage the code. The statement which control the flow of the execution is control or conditional statement.
One of such control statement is; the
if statement. This is a compound statement where it allows to execute the statements by give condition.
The conditional statement
if evaluates the given expression and allows to execute the statements in it’s code block. Even we can attach
else statement to the
if statement. When the expression is evaluated; the code within the
if statement will execute when the expression value is TRUE. Otherwise, the statements within the
else statement will execute.
>>> a = 20 >>> if a > 0: ... print("Positive number") ... else: ... print("Negative number") ... Positive number >>>
else statement is optional; if it presents, Python will execute the statements given in it’s code block when the expression’s result is FALSE. If
else statement NOT exists, Python will execute the statements after the
We can combine
if statements to evaluate multiple expressions. Depending on the result of the expression, the code within the particular
if block will be executed. Important thing to remember here is, maintain the proper indentation when using control statements within the control statement. The results will be unexpected, if NO proper indentation maintained.
>>> a = 20 >>> if a > 0: ... print("Positive number") ... if a%2 == 0: ... print("Even number") ... else: ... print("Negative number") ... Positive number Even number >>>
We can use
if statement within
else statement. This also useful to evaluate multiple expressions. This is equivalent to the switch and case statements in other languages.
>>> a = 1 >>> if a == 1: ... print("One") ... else: ... if a == 2: ... print("Two") ... else: ... if a == 3: ... print("Three") ... One >>>
if statements are properly indented to keep them aligned with respective
else statements. If you miss the indentation, you will see the wrong results. To simplify this, Python provides
elif statement; this is the short form of “else if” statement.
The simplified version of the above code, we can re-write as below.
>>> a = 2 >>> if a == 1: ... print("One") ... elif a == 2: ... print("Two") ... elif a == 3: ... print("Three") ... Two >>>
Observe that, how the code is neatly organized when using
We will discuss more topics as we go.