Recreating the sum symbol using python
In most cases, I would go for NumPy.
Implement a Python function f(t) that calculates the $t$-th summand.
Then run

import numpy as np
result = np.array([f(t) for t in range(1,m+1)]).sum()


This will be very fast, unless $m$ is so large that [f(t) for t in range(1,m+1)] does not fit into memory. In this case, I would follow your approach and use a for-loop:

result = 0
for t in range(1, m+1):
    result += f(t)