- Python Dictionaries
- Comparison Operators in Python
- Logical Operators in Python
- Conditional Statements in Python
- For Loop in Python
- While Loop in Python
- How to loop over python dictionaries and Numpy arrays
- What is NumPy in Python
- ndarray - Methods and Data Type
- NumPy - Methods to Create Arrays
- Python NumPy - Numerical Operations on Arrays
- Python NumPy - Indexing and Slicing Arrays

# While Loop in Python

The general format of the while statement is:

```
while (condition) :
statement
}
```

Note that a while loop may never execute the statement. The statement is executed repeatedly until condition becomes false.

Unlike `for`

loop which iterates over a list, for using `while`

loop you need to have an indicator variable `i`

and change its value within each iteration. Otherwise you will have an infinite loop.

### Example: While Loop

The following example shows how to calculate factorial of 10 using the while loop.

```
# Calculate 10! using a while loop
i = 10
f = 1
while ( i > 1 ) :
f = i*f
i = i-1
print(i, f)
```

We start with an iterator `i`

with a value of 10. Then each time the while loop iterates, we reduce the value of `i`

by 1. Finally, once `i`

becomes equal to 1, the while `loop`

ends. The results are shown below:

```
9 10
8 90
7 720
6 5040
5 30240
4 151200
3 604800
2 1814400
1 3628800
```

In the above example we used `while`

loop to calculate the factorial of a number. However, Python's math package also has a function that we can use to calculate the factorial. We will learn more math and statistical functions as we go along.

```
import math
math.factorial(n)
```

The above code will output the factorial of 10, i.e., 3628800.