按权重抽两个不同选项，入选概率还是原来的比例吗？

"""Exact Plackett-Luce probabilities for ordered draws without replacement."""
from fractions import Fraction as F
import itertools
import json
from pathlib import Path


def ordered_probability(weights,order):
    if not weights or not all(w>0 for w in weights):
        raise ValueError('strictly positive weights required')
    if len(order)>len(weights) or len(set(order))!=len(order):
        raise ValueError('distinct draws required')
    if any(type(i) is not int or not 0<=i<len(weights) for i in order):
        raise ValueError('unknown item')
    remaining=sum(weights); probability=F(1)
    for i in order:
        probability *= weights[i]/remaining
        remaining -= weights[i]
    return probability


def distribution(weights,k):
    if type(k) is not int or not 0<=k<=len(weights):
        raise ValueError('invalid sample size')
    return [(order,ordered_probability(weights,order))
            for order in itertools.permutations(range(len(weights)),k)]


def main():
    w=[F(1),F(2),F(3)]
    rows=distribution(w,2)
    assert sum(p for order,p in rows)==1
    first=[sum(p for order,p in rows if order[0]==i) for i in range(3)]
    inclusion=[sum(p for order,p in rows if i in order) for i in range(3)]
    assert first==[F(1,6),F(1,3),F(1,2)]
    assert inclusion==[F(5,12),F(11,15),F(17,20)] and sum(inclusion)==2
    subsets={}
    for order,p in rows:
        key=tuple(sorted(order)); subsets[key]=subsets.get(key,F(0))+p
    ab=ordered_probability(w,(0,1)); ba=ordered_probability(w,(1,0))
    assert ab==F(1,15) and ba==F(1,12) and subsets[(0,1)]==F(3,20)
    product_weighted=F(1*2,1*2+1*3+2*3)
    assert product_weighted!=subsets[(0,1)]
    assert distribution([10*x for x in w],2)==rows
    all_rows=distribution(w,3)
    assert [sum(p for order,p in all_rows if i in order) for i in range(3)]==[1,1,1]
    uniform=distribution([F(1)]*3,2)
    assert all(p==F(1,6) for order,p in uniform)
    rejected=0
    for weights,order in [([F(0),F(1)],(0,)),(w,(0,0)),(w,(3,))]:
        try: ordered_probability(weights,order)
        except ValueError: rejected+=1
    try: distribution(w,4)
    except ValueError: rejected+=1
    assert rejected==4
    report=dict(weights=list(map(str,w)),ordered=[dict(order=o,probability=str(p)) for o,p in rows],
        first_choice=list(map(str,first)),inclusion=list(map(str,inclusion)),
        subset_probabilities={str(k):str(v) for k,v in subsets.items()},
        product_weighted_ab=str(product_weighted),all_selected=[1,1,1],checks_passed=True)
    Path('report.json').write_text(json.dumps(report,indent=2)+'\n',encoding='utf-8')
    print(f'P(A then B)={float(ab):.6f}; P(B then A)={float(ba):.6f}')
    print(f'P(set A,B)={float(subsets[(0,1)]):.6f}; normalized product={float(product_weighted):.6f}')
    print('first-choice probabilities =',[round(float(p),6) for p in first])
    print('included in two draws =',[round(float(p),6) for p in inclusion])
    print('sum of inclusion probabilities =',float(sum(inclusion)))
    print('checks=PASS; report.json written')


if __name__=='__main__': main()