Write a Python function `square_perimeter` that calculates and returns the perimeter of a square given its side length as input.
The formula for the perimeter of a square is:
\[ \text{Perimeter} = 4 \times \text{side length} \]
#### Example Usage:
```python [main.nopy]
print(square_perimeter(10)) # Output: 40
print(square_perimeter(5)) # Output: 20
print(square_perimeter(4)) # Output: 16
```
#### Constraints:
- The input will always be a positive integer or float.
- The function should return the perimeter as a float or integer.