In Python programming, flow control is the order in which statements or blocks of code are executed at runtime based on a condition.
Table of contents
- Control Flow Statements
- If statement in Python
- for loop in Python
- While loop in Python
- Break Statement in Python
- Continue statement in python
- Pass statement in Python
Control Flow Statements
The flow control statements are divided into three categories
- Conditional statements
- Iterative statements.
- Transfer statements
In Python, condition statements act depending on whether a given condition is true or false. You can execute different blocks of codes depending on the outcome of a condition. Condition statements always evaluate to either True or False.
There are three types of conditional statements.
- if statement
- nested if-else
In Python, iterative statements allow us to execute a block of code repeatedly as long as the condition is True. We also call it a loop statements.
Python provides us the following two loop statement to perform some actions repeatedly
Let’s learn each one of them with the examples
In Python, transfer statements are used to alter the program’s way of execution in a certain manner. For this purpose, we use three types of transfer statements.
- break statement
- continue statement
If statement in Python
In control statements, The
if statement is the simplest form. It takes a condition and evaluates to either
If the condition is
True, then the True block of code will be executed, and if the condition is False, then the block of code is skipped, and The controller moves to the next line
Syntax of the
if condition: statement 1 statement 2 statement n
Let’s see the example of the if statement. In this example, we will calculate the square of a number if it greater than 5
number = 6 if number > 5: # Calculate square print(number * number) print('Next lines of code')
36 Next lines of code
If – else statement
if-else statement checks the condition and executes the
if block of code when the condition is True, and if the condition is False, it will execute the
else block of code.
Syntax of the
if condition: statement 1 else: statement 2
If the condition is
True, then statement 1 will be executed If the condition is
False, statement 2 will be executed. See the following flowchart for more detail.
password = input('Enter password ') if password == "PYnative@#29": print("Correct password") else: print("Incorrect Password")
Enter password PYnative@#29 Correct password
Enter password PYnative Incorrect Password
Chain multiple if statement in Python
In Python, the
if-elif-else condition statement has an
elif blocks to chain multiple conditions one after another. This is useful when you need to check multiple conditions.
With the help of
if-elif-else we can make a tricky decision. The
elif statement checks multiple conditions one by one and if the condition fulfills, then executes that code.
Syntax of the
if condition-1: statement 1 elif condition-2: stetement 2 elif condition-3: stetement 3 ... else: statement
def user_check(choice): if choice == 1: print("Admin") elif choice == 2: print("Editor") elif choice == 3: print("Guest") else: print("Wrong entry") user_check(1) user_check(2) user_check(3) user_check(4)
Admin Editor Guest Wrong entry
Nested if-else statement
In Python, the nested
if-else statement is an if statement inside another
if-else statement. It is allowed in Python to put any number of
if statements in another
Indentation is the only way to differentiate the level of nesting. The nested
if-else is useful when we want to make a series of decisions.
Syntax of the nested-
if conditon_outer: if condition_inner: statement of inner if else: statement of inner else: statement ot outer if else: Outer else statement outside if block
Example: Find a greater number between two numbers
num1 = int(input('Enter first number ')) num2 = int(input('Enter second number ')) if num1 >= num2: if num1 == num2: print(num1, 'and', num2, 'are equal') else: print(num1, 'is greater than', num2) else: print(num1, 'is smaller than', num2)
Enter first number 56 Enter second number 15 56 is greater than 15
Enter first number 29 Enter second number 78 29 is smaller than 78
Single statement suites
Whenever we write a block of code with multiple if statements, indentation plays an important role. But sometimes, there is a situation where the block contains only a single line statement.
Instead of writing a block after the colon, we can write a statement immediately after the colon.
number = 56 if number > 0: print("positive") else: print("negative")
Similar to the
if statement, while loop also consists of a single statement, we can place that statement on the same line.
x = 1 while x <= 5: print(x,end=" "); x = x+1
1 2 3 4 5
for loop in Python
Using for loop, we can iterate any sequence or iterable variable. The sequence can be string, list, dictionary, set, or tuple.
Read the Complete guide on Python for loop.
for element in sequence: body of for loop
Example to display first ten numbers using for loop
for i in range(1, 11): print(i)
1 2 3 4 5 6 7 8 9 10
Also, read Nested loops in Python.
While loop in Python
In Python, The while loop statement repeatedly executes a code block while a particular condition is true.
In a while-loop, every time the condition is checked at the beginning of the loop, and if it is true, then the loop’s body gets executed. When the condition became False, the controller comes out of the block.
Read the Complete guide on Python while loop.
Syntax of while-loop
while condition : body of while loop
Example to calculate the sum of first ten numbers
num = 10 sum = 0 i = 1 while i <= num: sum = sum + i i = i + 1 print("Sum of first 10 number is:", sum)
Sum of first 10 number is: 55
Break Statement in Python
Read: Complete guide on Python Break, Continue, and Pass.
The break statement is used inside the loop to exit out of the loop. It is useful when we want to terminate the loop as soon as the condition is fulfilled instead of doing the remaining iterations. It reduces execution time. Whenever the controller encountered a break statement, it comes out of that loop immediately
Let’s see how to break a for a loop when we found a number greater than 5.
Example of using a break statement
for num in range(10): if num > 5: print("stop processing.") break print(num)
0 1 2 3 4 5 stop processing.
Continue statement in python
The continue statement is used to skip the current iteration and
continue with the next iteration.
Let’s see how to skip a for a loop iteration if the number is 5 and continue executing the body of the loop for other numbers.
Example of a
for num in range(3, 8): if num == 5: continue else: print(num)
3 4 6 7
Pass statement in Python
The pass is the keyword In Python, which won’t do anything. Sometimes there is a situation in programming where we need to define a syntactically empty block. We can define that block with the pass keyword.
A pass statement is a Python null statement. When the interpreter finds a pass statement in the program, it returns no operation. Nothing happens when the
pass statement is executed.
It is useful in a situation where we are implementing new methods or also in exception handling. It plays a role like a placeholder.
months = ['January', 'June', 'March', 'April'] for mon in months: pass print(months)
['January', 'June', 'March', 'April']