用推导式近似黎曼和

我跟随sicp用黎曼和计算积分:

#+begin_src ipython :session sicp :results output
def integral(f, a, b, dx):
    add_dx = lambda x: x + dx
    return sum_recur(f, a+(dx/2), add_dx, b) * dx

from functools import lru_cache
@lru_cache(maxsize=None)
def sum_recur(term, a, next, b):
    if a > b: return 0
    return term(a) + sum_recur(term, next(a), next, b)

def cube(x): return x ** 3

print(integral(cube, 0, 1, 0.01))

#+end_src

#+RESULTS:
: 0.24998750000000042

它工作正常，但当实现它与列表理解

#+begin_src ipython :session sicp :results output
def integral(f, a, b, dx):
    return sum(a+dx/2+n*dx for n in range(b-1)) * dx
print(integral(cube, 0, 1, 0.001))
#+end_src

#+RESULTS:
: 5e-07

它没有像预期的那样工作，有什么问题吗? 问题来源StackOverflow 地址：/questions/59383439/approximate-the-riemann-sum-with-comprehensions