statistics module NormalDist.quantiles(0) should raise statistics error instead of returning empty list and makes redundant checks

[lbaumbauer]

Bug report

Bug description:

import statistics

d = statistics.NormalDist()

print(d.quantiles(0))

output:
[]

2. The called function inv_cdf checks for p <= 0 or .. during every iteration of the loop rather than once, even though all values of p are guaranteed to be in the range through the way they are generated as i / n.

self.inv_cdf(i / n) for i in range(1, n)

inv_cdf(self, p)
...
 if p <= 0.0 or p >= 1.0

It makes more sense to call the implementation _normal_dist_inv_cdf(p, self._mu, self._sigma) directly.

CPython versions tested on:

3.13

Operating systems tested on:

Other

[ayishaatwork]

I'd like to work on this bug if it's still available.

I'll first verify the current behavior and review the implementation of NormalDist.quantiles(), then prepare a patch and corresponding tests if the proposed optimization is accepted. Could I be assigned to this issue?