In python, if statement is useful when you want to execute the block of code/statements only when the defined condition is true.
Generally, if you want to execute the different statements based on various conditions, we will call them control flow statements. For example, showing a message either "Good Morning" or "Good Evening" based on the day's time is like executing the different statements based on the time.
In python, if…else, for loop, while loop, break, continue, and pass statements will come under the control flow statements because these will control the execution flow of programs.
In python, if keyword is useful to define the conditional if statements. Following is the syntax of defining if statement in python.
If you observe the above if statement syntax, the statements inside of the if condition will execute only when the boolean_expression returns True otherwise, the defined statements will not be executed.
In python, to create if condition with a block of statements, you need to follow the indentation. Here, the colon (:) symbol will indicate the start of the code block. After typing the colon (:) symbol and click on Enter, it will increase the indentation to create the statements inside of if statement.
To execute the multiple statements inside of if condition, follow the same indentation for all the statements. To end if block, reduce the indentation so that the subsequent statements will be executed as outside of if statement.
In other programming languages, indentation is just for code readability, and curly braces { } are used to indicate the block of statements, but in python, indentation is mandatory to indicate the block of statements.
Following is the flow chart diagram of if statement process flow in python.
If you observe the above if statement flow chart diagram, the block of statements will execute only when the defined condition is true otherwise if statement will skip the execution of defined statements.
Following is the example of if statement in python to execute the block of statements based on the defined Boolean expression.
If you observe the above example, we defined multiple if statements with boolean expressions and followed the indentation to define the block of statements inside if statements.
When you execute the above python program, you will get the result as shown below.
If you skip the indentation while creating if statements, you will get build errors (IndentationError).
Following is the example of defining if statements in python without indentation.
If you observe the above example, we defined if statements without indentation. So, when we try to execute the above python program, we will get build errors like “excepted an indented block”.
To know more about specifying the indentation in python, refer to Python basic syntaxes.
In python, you can use logical operators such as and, or, not to combine multiple conditions into a single expression in if statement and execute the block of statements when the defined conditions are evaluated to True or False based on your requirements.
The logical and operator is useful to combine the multiple conditions in python if statement. As discussed, the logical and operator will return True only when both operands are True.
Following is the example of using and operator in the boolean expression of python if statement.
If you observe the above example, we used logical and operator to combine multiple conditions in a boolean expression of if statement.
When you execute the above python program, you will get the result as shown below.
Like logical and operator, the logical or operator is also useful to combine multiple conditions in a boolean expression. The logical or operator will return True if either of an operand is True.
Following is the example of using or operator in the boolean expression of Python if statement.
If you observe the above example, we used logical or operator to combine multiple conditions in the boolean expression of if statement.
When you execute the above python program, you will get the result as shown below.
Same as logical and, logical or operators, you can use logical not operator in python if statement to execute the block of statements when the defined condition evaluates True or False based on your requirements. The logical not operator will reverse the result if an operand is True it will return False and vice-versa.
Following is the example of using not operator in the boolean expression of python if statement.
If you observe the above example, we used logical not operator in the boolean expression of if statement.
When you execute the above python program, you will get the result as shown below.
If you have only one line statement to execute, you can write python if statement in a single line like as shown below.
When you execute the above python program, you will get the result as shown below.
In python, if you create if statements inside of another if statements, we will call it nested if statements.
Following is the example of creating nested if statements in python.
When you execute the above python program, you will get the result as shown below.
This is how you can define if statement in python to execute the block of statements based on the defined condition evaluation, i.e., either True or False.