In this example, we will learn how to calculate the area of a triangle with three given sides in Python.

### Source Code

```
#! /usr/bin/env python3
# -*- coding: utf-8 -*-
import math
print("Please input the lenght of three sides: ")
a = []
for i in range(0, 3):
b = int(input("Length: "))
a.append(b)
s = sum(a) / 2
area = math.sqrt(s * (s - a[0]) * (s - a[1]) * (s - a[2]))
print("The area of the triangle is: ", round(area,2))
```

Output:

```
Please input the lenght of three sides:
Length: 3
Length: 4
Length: 5
The area of the triangle is: 6.0
Please input the lenght of three sides:
Length: 8
Length: 9
Length: 12
The area of the triangle is: 36.0
```