练习四十八：面向对象执行效率

按执行效率从高到底排序：f2,f1,f3
要求证明这个答案是对的
所以要分析代码的性能，计算出性能时间

方法一：使用python性能分析模块 cProfile

  1 import random
  2 def f1(lin):
  3     l1 = sorted(lin)
  4     l2 = [i for i in l1 if i<0.5]
  5     return [i*i for i in l2]
  6 def f2(lin):
  7     l1 = [i for i in lin if i<0.5]
  8     l2 = sorted(l1)
  9     return [i*i for i in l2]
 10 def f3(lin):
 11     l1 = [i*i for i in lin]
 12     l2 = sorted(l1)
 13     return [i for i in l1 if i<(0.5*0.5)]
 14 
 15 if __name__ == "__main__":
 16     import cProfile
 17     lin = [random.random() for i in range(10000)]
 18     cProfile.run('f1(lin)')
 19     cProfile.run("f2(lin)")
 20     cProfile.run('f3(lin)')
 21

执行结果：

         7 function calls in 0.007 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.007    0.007 <ipython-input-2-b2915fa74d28>:2(f1)
        1    0.001    0.001    0.001    0.001 <ipython-input-2-b2915fa74d28>:4(<listcomp>)
        1    0.000    0.000    0.000    0.000 <ipython-input-2-b2915fa74d28>:5(<listcomp>)
        1    0.000    0.000    0.007    0.007 <string>:1(<module>)
        1    0.000    0.000    0.007    0.007 {built-in method builtins.exec}
        1    0.006    0.006    0.006    0.006 {built-in method builtins.sorted}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}


         7 function calls in 0.005 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.004    0.004 <ipython-input-2-b2915fa74d28>:6(f2)
        1    0.001    0.001    0.001    0.001 <ipython-input-2-b2915fa74d28>:7(<listcomp>)
        1    0.001    0.001    0.001    0.001 <ipython-input-2-b2915fa74d28>:9(<listcomp>)
        1    0.000    0.000    0.005    0.005 <string>:1(<module>)
        1    0.000    0.000    0.005    0.005 {built-in method builtins.exec}
        1    0.003    0.003    0.003    0.003 {built-in method builtins.sorted}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}


         7 function calls in 0.008 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.008    0.008 <ipython-input-2-b2915fa74d28>:10(f3)
        1    0.001    0.001    0.001    0.001 <ipython-input-2-b2915fa74d28>:11(<listcomp>)
        1    0.001    0.001    0.001    0.001 <ipython-input-2-b2915fa74d28>:13(<listcomp>)
        1    0.000    0.000    0.008    0.008 <string>:1(<module>)
        1    0.000    0.000    0.008    0.008 {built-in method builtins.exec}
        1    0.005    0.005    0.005    0.005 {built-in method builtins.sorted}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}

方法二：使用time模块，我们只修改主函数

  1 if __name__ == "__main__":
  2     import time
  3     lin = [random.random() for i in range(10000)]
  4     t1 = time.time()
  5     f1(lin)
  6     t2 = time.time()
  7     f2(lin)
  8     t3 = time.time()
  9     f3(lin)
 10     t4 = time.time()
 11     print('f1运行时间：',t2-t1)
 12     print('f2运行时间：',t3-t2)
 13     print('f3运行时间：',t4-t3)

执行结果：

f1运行时间： 0.0059967041015625
f2运行时间： 0.003997087478637695
f3运行时间： 0.00999307632446289