If, If...else, If...elif...else, Nested If

What is a selection statement in Python?

• In some cases in programming, Our program has to decide whether the following block of codes needs to be executed or not, based on some conditions.

• Such Decision making statements/selection statements decide the direction of the flow of program execution.

• Decision making statements/selection statements available in Python are

• if (Simple If)

• if-else

• else-if ladder

• Nested if

• In python, body statements inside the selection statement are indicated by the indentation. The very first unindented line marks the end of the selection statements.

If (Simple If):

• It is a simple conditional statement that is used for decision-making.

• If the evaluated condition is true, the statements inside the if block will be executed.

• In if statement, we have only one statement to select. Because of this, it is called a One-way Selection statement.

• Syntax:

                                if (condition):

                                         Statement 1

                                          .......

                                         Statement  n

Simple If statement

Output

If-else:

• It is also a conditional statement that is used to select between two sets of statements based on the results of the evaluated condition.

• If the evaluated condition is true, then the statements inside the if block will be executed. Otherwise, the statements inside the else block will be executed.

• Since we have two statements to select based on the condition, hence it is called a Two-way Selection statement.

• Syntax:

                                 if (condition):

                                         Statement 1

                                          .......

                                         Statement  n

                                 else:

                                        Statement 1

                                        ..........

                                        Statement n

If...else statement

Output

Else-if (elif) ladder:

• A conditional statement is used to select a statement from multiple sets of statements based on multiple test conditions.

• The different test conditions are provided inside each if statement.

• If any of the evaluated conditions is true, then statement inside the corresponding if block will be executed and the control comes out of the else-if ladder.

• If none of the conditions is true, then the statements inside the else block will be executed.

• Since we have multiple sets of statements to select based on the test condition. Hence it is also called a multi-way selection statement.

• As soon as a true condition is found, the statement associated with it is executed skipping the rest of the conditions and the statements.

• Syntax:

                                 if (condition):

                                         Statement 1

                                          .......

                                         Statement  n

                                 elif (condition):

                                        Statement 1

                                        ..........

                                        Statement n

                                 else:

                                        Statement 1

                                        ..........

                                        Statement n

Elif statement

Output

Nested if:

• An if statement inside another if statement is known as nested if statements.

• Let's understand with an example.

Nested If

Output