Question: I'm trying to make a calculator for something, but the formulas use a sigma, I have no idea how to do a sigma in python, is there an operator for it?
Ill put a link here with a page that has the formulas on it for illustration:<http://fromthedepths.gamepedia.com/User:Evil4Zerggin/Advanced_cannon>

Answer: 
A sigma (∑) is a [Summation](https://en.wikipedia.org/wiki/Summation) operator. It evaluates a certain expression many times, with slightly different variables, and returns the **sum** of all those expressions.

For example, in the [Ballistic coefficient](http://fromthedepths.gamepedia.com/User:Evil4Zerggin/Advanced_cannon#Ballistic_coefficient) formula

[![enter image description here](https://i.stack.imgur.com/fPTfk.png)](https://i.stack.imgur.com/fPTfk.png)

The Python implementation would look something like this:

```
# Just guessing some values. You have to search the actual values in the wiki.
ballistic_coefficients = [0.3, 0.5, 0.1, 0.9, 0.1]

total_numerator = 0
total_denominator = 0
for i, coefficient in enumerate(ballistic_coefficients):
    total_numerator += 2**(-i) * coefficient
    total_denominator += 2**(-i)
print('Total:', total_numerator / total_denominator)

```

You may want to look at the [`enumerate` function](https://docs.python.org/3/library/functions.html#enumerate), and beware precision problems.
```
import numpy as np

def sigma(s,e):
  x = np.arange(s,e)
  return np.sum([x+1])

```