您能帮助确定此代码的瓶颈吗？我正在解决项目Euler的问题＃7，并且我无法理解为什么这个解决方案需要这么长时间（30s）。我知道有更好的解决方案，我只想更多地了解为什么会这样，特别是那么糟糕。
def primes(n):
primes = set([2])
count = 1
i = 1
while count < n:
i += 2
if not any([i % num == 0 for num in primes]):
primes.add(i)
count += 1
print i
cProfile.run("primes(10001)") #slow! 30s
个人资料如下：
62374 function calls in 34.605 seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.000 0.000 34.605 34.605 <string>:1(<module>)
1 34.273 34.273 34.605 34.605 problem_7.py:8(primes)
52371 0.328 0.000 0.328 0.000 {any}
10000 0.004 0.000 0.004 0.000 {method 'add' of 'set' objects}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
答案 0 :(得分：0)
我实施了一些调整来帮助解决问题。请参阅下面的评论和结果。在所有情况下，我都将累加器从名为primes（隐藏其函数名称）改为名为ps。我没有测试，看看这是否改善了性能，我只是讨厌阴影名称：o）
# Your original code
def prime_orig(n):
ps = set([2])
count = 1
i = 1
while count < n:
i += 2
if not any([i % num == 0 for num in ps]):
ps.add(i)
count += 1
# replace the set accum with a list, per @Sheshnath's comment
def prime_list(n):
ps = [2]
count = 1
i = 1
while count < n:
i += 2
if not any([i % num == 0 for num in ps]):
ps.append(i)
count += 1
# replace the listcomp with a genexp
def prime_genexp(n):
ps = set([2])
count = 1
i = 1
while count < n:
i += 2
if not any(i % num == 0 for num in ps):
ps.add(i)
count += 1
# both optimizations at once
def prime_genexp_list(n):
ps = [2]
count = 1
i = 1
while count < n:
i += 2
if not any(i % num == 0 for num in ps):
ps.append(i)
count += 1
结果：
cProfile.run('prime_orig(10001)')
114746 function calls in 27.283 seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.701 0.701 27.283 27.283 <ipython-input-2-3059f1e23ab4>:1(prime_orig)
52371 26.330 0.001 26.330 0.001 <ipython-input-2-3059f1e23ab4>:7(<listcomp>)
1 0.000 0.000 27.283 27.283 <string>:1(<module>)
52371 0.250 0.000 0.250 0.000 {built-in method builtins.any}
1 0.000 0.000 27.283 27.283 {built-in method builtins.exec}
10000 0.003 0.000 0.003 0.000 {method 'add' of 'set' objects}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
cProfile.run('prime_list(10001)')
114746 function calls in 24.523 seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.666 0.666 24.523 24.523 <ipython-input-2-3059f1e23ab4>:11(prime_list)
52371 23.625 0.000 23.625 0.000 <ipython-input-2-3059f1e23ab4>:17(<listcomp>)
1 0.000 0.000 24.523 24.523 <string>:1(<module>)
52371 0.231 0.000 0.231 0.000 {built-in method builtins.any}
1 0.000 0.000 24.523 24.523 {built-in method builtins.exec}
10000 0.001 0.000 0.001 0.000 {method 'append' of 'list' objects}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
cProfile.run('prime_genexp(10001)')
50627376 function calls in 10.577 seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.040 0.040 10.577 10.577 <ipython-input-2-3059f1e23ab4>:21(prime_genexp)
50565001 7.060 0.000 7.060 0.000 <ipython-input-2-3059f1e23ab4>:27(<genexpr>)
1 0.000 0.000 10.577 10.577 <string>:1(<module>)
52371 3.475 0.000 10.530 0.000 {built-in method builtins.any}
1 0.000 0.000 10.577 10.577 {built-in method builtins.exec}
10000 0.002 0.000 0.002 0.000 {method 'add' of 'set' objects}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}
cProfile.run('prime_genexp_list(10001)')
50400891 function calls in 9.781 seconds
Ordered by: standard name
ncalls tottime percall cumtime percall filename:lineno(function)
1 0.040 0.040 9.781 9.781 <ipython-input-2-3059f1e23ab4>:31(prime_genexp_list)
50338516 6.272 0.000 6.272 0.000 <ipython-input-2-3059f1e23ab4>:37(<genexpr>)
1 0.000 0.000 9.781 9.781 <string>:1(<module>)
52371 3.468 0.000 9.735 0.000 {built-in method builtins.any}
1 0.000 0.000 9.781 9.781 {built-in method builtins.exec}
10000 0.001 0.000 0.001 0.000 {method 'append' of 'list' objects}
1 0.000 0.000 0.000 0.000 {method 'disable' of '_lsprof.Profiler' objects}