How Can I Efficiently Calculate the Cumulative Sum of a List of Numbers in Python?

Finding the Cumulative Sum of Numbers in a List

Problem:
Given a list of numbers, we want to find the cumulative sum, which means summing up the numbers one by one from the beginning of the list. For instance, if we have a list [4, 6, 12], we want to get [4, 4 6, 4 6 12] resulting in [4, 10, 22].

Answer:

For numerical operations on arrays, it's recommended to consider NumPy, a powerful Python library. It features a convenient cumulative sum function, cumsum:

import numpy as np

a = [4,6,12]

np.cumsum(a)
#array([4, 10, 22])

NumPy often outperforms pure Python for such tasks. Here's a comparison with another function, accumu:

In [136]: timeit list(accumu(range(1000)))
10000 loops, best of 3: 161 us per loop

In [137]: timeit list(accumu(xrange(1000)))
10000 loops, best of 3: 147 us per loop

In [138]: timeit np.cumsum(np.arange(1000))
100000 loops, best of 3: 10.1 us per loop

While NumPy offers speed advantages, it's important to remember that a dependency may not be necessary if NumPy is only required for a single task.

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