# Python While Loops

In coding, loops are designed to execute a specified code block repeatedly. We'll learn how to construct a while loop in Python, the syntax of a while loop, loop controls like break and continue, and other exercises in this tutorial.

## Introduction of Python While Loop

The Python while loop iteration of a code block is executed as long as the given condition, i.e., conditional_expression, is true.

If we don't know how many times we'll execute the iteration ahead of time, we can write an indefinite loop.

Syntax of Python While Loop

The given condition, i.e., conditional_expression, is evaluated initially in the Python while loop. Then, if the conditional expression gives a boolean value True, the while loop statements are executed. The conditional expression is verified again when the complete code block is executed. This procedure repeatedly occurs until the conditional expression returns the boolean value False.

• The statements of the Python while loop are dictated by indentation.
• The code block begins when a statement is indented & ends with the very first unindented statement.
• Any non-zero number in Python is interpreted as boolean True. False is interpreted as None and 0.

## Python While Loop Example

Here we will sum of squares of the first 15 natural numbers using a while loop.

Code

Output:

```The sum of squares is 1240
```

Provided that our counter parameter i gives boolean true for the condition, i less than or equal to num, the loop repeatedly executes the code block i number of times.

Next is a crucial point (which is mostly forgotten). We have to increment the counter parameter's value in the loop's statements. If we don't, our while loop will execute itself indefinitely (a never-ending loop).

Finally, we print the result using the print statement.

## Exercises of Python While Loop

### Prime Numbers and Python While Loop

Using a while loop, we will construct a Python program to verify if the given integer is a prime number or not.

Code

Output:

```34 is not a PRIME number
12 is not a PRIME number
54 is not a PRIME number
23 is a PRIME number
75 is not a PRIME number
34 is not a PRIME number
11 is a PRIME number
```

### Multiplication Table using While Loop

In this example, we will use the while loop for printing the multiplication table of a given number.

Code

Output:

```The Multiplication Table of:  21
21 x 1 = 21
21 x 2 = 42
21 x 3 = 63
21 x 4 = 84
21 x 5 = 105
21 x 6 = 126
21 x 7 = 147
21 x 8 = 168
21 x 9 = 189
21 x 10 = 210
```

### Python While Loop with List

We will use a Python while loop to square every number of a list

Code

```[36, 16, 1, 25, 9]
```

In the preceding example, we execute a while loop over a given list of integers that will repeatedly run as long as an element in the list is found.

## Python While Loop Multiple Conditions

We'll need to recruit logical operators to combine two or more expressions specifying conditions into a single while loop. This instructs Python on collectively analyzing all of the given expressions of conditions.

We can construct a while loop with multiple conditions in this example. We have given two conditions and a and keyword, meaning until both conditions give boolean True, the loop will execute the statements.

Code

Output:

```(15, -9)
(13, -6)
(11, -3)
```

Let's look at another example of multiple conditions with an OR operator.

Code

Output:

```(15, -9)
(13, -6)
(11, -3)
(9, 0)
(7, 3)
(5, 6)
```

We can also group multiple logical expressions in the while loop, as shown in this example.

Code

Output:

```Number of iterations: 0
Number of iterations: 1
Number of iterations: 2
Number of iterations: 3
```

## Single Statement While Loop

Similar to the if statement syntax, if our while clause consists of one statement, it may be written on the same line as the while keyword.

Here is the syntax and example of a one-line while clause -

## Loop Control Statements

Now we will discuss the loop control statements in detail. We will see an example of each control statement.

### Continue Statement

It returns the control of the Python interpreter to the beginning of the loop.

Code

Output:

```Current Letter: W
Current Letter: h
Current Letter: l
Current Letter:
Current Letter: L
Current Letter: p
Current Letter: s
```

### Break Statement

It stops the execution of the loop when the break statement is reached.

Code

Output:

```Current Letter:  P
Current Letter:  y
Current Letter:  t
Current Letter:  h
Current Letter:  o
```

### Pass Statement

Pass statements are used to create empty loops. Pass statement is also employed for classes, functions, and empty control statements.

Code

Output:

```Last Letter: s
```

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