python算法教程（第二章）

[TOC]

本章两个话题

1. 渐近记法（asymptotic notation），主要关注的是运行时间的本质。
2. 树(tree)、图(graph)这两种数据结构在python中的实现方式。

实证式算法评估

1. 使用timeit模块来计时

• 快速认识模块
• 模块与包

mymodule.py

def myfunction():
    sum1 = 0
    for i in range(0,10000):
        sum1 += i
    return sum1

计时。关于timeit模块
python -m timeit -s"import mymodule as m" "m.myfunction()"

• -s S, --setup=S
  执行时初始语句(默认是pass)

2. 使用profile找出瓶颈

import cProfile
def main():
    list1 = ['physics','chemistry',1990,1997,2000]
    print(list1)
    for i in list1:
        print(i,end=' ')

def runMain():
    cProfile.run('main()')
if __name__ == '__main__':
    #main()
    runMain()

result:

['physics', 'chemistry', 1990, 1997, 2000]
physics chemistry 1990 1997 2000          630 function calls in 0.043 seconds

   Ordered by: standard name

   ncalls  tottime  percall  cumtime  percall filename:lineno(function)
        1    0.000    0.000    0.043    0.043 :1()
       12    0.000    0.000    0.043    0.004 PyShell.py:1336(write)
       91    0.000    0.000    0.000    0.000 rpc.py:150(debug)
       13    0.000    0.000    0.043    0.003 rpc.py:213(remotecall)
       13    0.000    0.000    0.002    0.000 rpc.py:223(asynccall)
       13    0.000    0.000    0.041    0.003 rpc.py:243(asyncreturn)
       13    0.000    0.000    0.000    0.000 rpc.py:249(decoderesponse)
       13    0.000    0.000    0.041    0.003 rpc.py:287(getresponse)
       13    0.000    0.000    0.000    0.000 rpc.py:295(_proxify)
       13    0.000    0.000    0.041    0.003 rpc.py:303(_getresponse)
       13    0.000    0.000    0.000    0.000 rpc.py:325(newseq)
       13    0.000    0.000    0.001    0.000 rpc.py:329(putmessage)
       12    0.000    0.000    0.001    0.000 rpc.py:551(__getattr__)
        1    0.000    0.000    0.001    0.001 rpc.py:569(__getmethods)
       13    0.000    0.000    0.000    0.000 rpc.py:57(dumps)
       12    0.000    0.000    0.000    0.000 rpc.py:592(__init__)
       12    0.000    0.000    0.041    0.003 rpc.py:597(__call__)
       26    0.000    0.000    0.000    0.000 threading.py:1221(current_thread)
       13    0.000    0.000    0.000    0.000 threading.py:210(__init__)
       13    0.000    0.000    0.040    0.003 threading.py:258(wait)
       13    0.000    0.000    0.000    0.000 threading.py:75(RLock)
        1    0.000    0.000    0.043    0.043 timeit_test.py:2(main)
       13    0.000    0.000    0.000    0.000 {built-in method allocate_lock}
        1    0.000    0.000    0.043    0.043 {built-in method exec}
       26    0.000    0.000    0.000    0.000 {built-in method get_ident}
       26    0.000    0.000    0.000    0.000 {built-in method isinstance}
       39    0.000    0.000    0.000    0.000 {built-in method len}
       13    0.000    0.000    0.000    0.000 {built-in method pack}
        6    0.000    0.000    0.043    0.007 {built-in method print}
       13    0.000    0.000    0.000    0.000 {built-in method select}
       13    0.000    0.000    0.000    0.000 {method '_acquire_restore' of '_thread.RLock' objects}
       13    0.000    0.000    0.000    0.000 {method '_is_owned' of '_thread.RLock' objects}
       13    0.000    0.000    0.000    0.000 {method '_release_save' of '_thread.RLock' objects}
       13    0.000    0.000    0.000    0.000 {method 'acquire' of '_thread.RLock' objects}
       26    0.040    0.002    0.040    0.002 {method 'acquire' of '_thread.lock' objects}
       13    0.000    0.000    0.000    0.000 {method 'append' of 'collections.deque' objects}
        1    0.000    0.000    0.000    0.000 {method 'disable' of '_lsprof.Profiler' objects}
       13    0.000    0.000    0.000    0.000 {method 'dump' of '_pickle.Pickler' objects}
       12    0.000    0.000    0.000    0.000 {method 'get' of 'dict' objects}
       13    0.000    0.000    0.000    0.000 {method 'getvalue' of '_io.BytesIO' objects}
       13    0.000    0.000    0.000    0.000 {method 'release' of '_thread.RLock' objects}
       13    0.001    0.000    0.001    0.000 {method 'send' of '_socket.socket' objects}

待续....