對(duì)于某個(gè)城市的出租車(chē)數(shù)據(jù)，一天就有33210000條記錄，如何將每輛車(chē)的數(shù)據(jù)單獨(dú)拎出來(lái)放到一個(gè)專(zhuān)屬的文件中呢？

思路很簡(jiǎn)單：

就是循環(huán)33210000條記錄，將每輛車(chē)的數(shù)據(jù)搬運(yùn)到它該去的文件中。

但是對(duì)于3000多萬(wàn)條數(shù)據(jù)，一個(gè)一個(gè)循環(huán)太消耗時(shí)間，我花了2個(gè)小時(shí)才搬運(yùn)了60萬(wàn)數(shù)據(jù)，算算3000萬(wàn)我需要花費(fèi)100個(gè)小時(shí)，也就需要4-5天。并且還需要保證這五天全天開(kāi)機(jī)，不能出現(xiàn)卡機(jī)的事故。

因此，需要使用并行進(jìn)行for循環(huán)的技巧：

由于3000萬(wàn)數(shù)據(jù)放到csv中導(dǎo)致csv打不開(kāi)，因此我就把一個(gè)csv通過(guò)split軟件將其切分成每份60萬(wàn)，共53個(gè)csv。

我原來(lái)的思路是讀取文件夾，獲取由每一個(gè)60萬(wàn)的csv文件組成的列表，再分別對(duì)每一個(gè)60萬(wàn)的csv進(jìn)行處理。實(shí)質(zhì)上還是循環(huán)33210000次，并行for循環(huán)就是同時(shí)處理幾個(gè)60萬(wàn)的csv文件，就能成倍的減少時(shí)間消耗。

并行進(jìn)行for循環(huán)是受下面的方法啟發(fā)：

我之前的做法類(lèi)似這樣：

words = [’apple’, ’bananan’, ’cake’, ’dumpling’] for word in words: print word

并行for循環(huán)類(lèi)似這樣：

from multiprocessing.dummy import Pool as ThreadPoolitems = list()pool = ThreadPool()pool.map(process, items)pool.close()pool.join()

其中,process是進(jìn)行處理的函數(shù)

實(shí)例代碼如下：

# -*- coding: utf-8 -*-import timefrom multiprocessing.dummy import Pool as ThreadPooldef process(item): print(’正在并行for循環(huán)’) print(item) time.sleep(5)items = [’apple’, ’bananan’, ’cake’, ’dumpling’]pool = ThreadPool()pool.map(process, items)pool.close()pool.join()

補(bǔ)充知識(shí)：Python3用多線(xiàn)程替代for循環(huán)提升程序運(yùn)行速度

優(yōu)化前后新老代碼如下：

from git_tools.git_tool import get_collect_projects, QQNews_Gitfrom threading import Thread, Lockimport datetimebase_url = 'http://git.xx.com'project_members_commits_lang_info = {}lock = Lock()threads = []’’’Author:zenkilan’’’def count_time(func): def took_up_time(*args, **kwargs): start_time = datetime.datetime.now() ret = func(*args, **kwargs) end_time = datetime.datetime.now() took_up_time = (end_time - start_time).total_seconds() print(f'{func.__name__} execution took up time:{took_up_time}') return ret return took_up_timedef get_project_member_lang_code_lines(git, member, begin_date, end_date): global project_members_commits_lang_info global lock member_name = member['username'] r = git.get_user_info(member_name) if not r['id']: return user_commits_lang_info = git.get_commits_user_lang_diff_between(r['id'], begin_date, end_date) if len(user_commits_lang_info) == 0: return lock.acquire() project_members_commits_lang_info.setdefault(git.project, dict()) project_members_commits_lang_info[git.project][member_name] = user_commits_lang_info lock.release()def get_project_lang_code_lines(project, begin_date, end_date): global threads git = QQNews_Git(project[1], base_url, project[0]) project_members = git.get_project_members() if len(project_members) == 0: return for member in project_members: thread = Thread(target=get_project_member_lang_code_lines, args=(git, member, begin_date, end_date)) threads.append(thread) thread.start()@count_timedef get_projects_lang_code_lines(begin_date, end_date): ''' 獲取項(xiàng)目代碼行語(yǔ)言相關(guān)統(tǒng)計(jì)——新方法（提升效率） 應(yīng)用多線(xiàn)程替代for循環(huán) 并發(fā)訪(fǎng)問(wèn)共享外部資源 :return: ''' global project_members_commits_lang_info global threads for project in get_collect_projects(): thread = Thread(target=get_project_lang_code_lines, args=(project, begin_date, end_date)) threads.append(thread) thread.start()@count_timedef get_projects_lang_code_lines_old(begin_date, end_date): ''' 獲取項(xiàng)目代碼行語(yǔ)言相關(guān)統(tǒng)計(jì)——老方法（耗時(shí)嚴(yán)重） 使用最基本的思路進(jìn)行編程 雙層for循環(huán)嵌套并且每層都包含耗時(shí)操作 :return: ''' project_members_commits_lang_info = {} for project in get_collect_projects(): git = QQNews_Git(project[1], base_url, project[0]) project_members = git.get_project_members() user_commits_lang_info_dict = {} if len(project_members) == 0: continue for member in project_members: member_name = member['username'] r = git.get_user_info(member_name, debug=False) if not r['id']:continue try:user_commits_lang_info = git.get_commits_user_lang_diff_between(r['id'], begin_date, end_date)if len(user_commits_lang_info) == 0: continueuser_commits_lang_info_dict[member_name] = user_commits_lang_infoproject_members_commits_lang_info[git.project] = user_commits_lang_info_dict except:pass return project_members_commits_lang_infodef test_results_equal(resultA, resultB): ''' 測(cè)試方法 :param resultA: :param resultB: :return: ''' print(resultA) print(resultB) assert len(str(resultA)) == len(str(resultB))if __name__ == ’__main__’: from git_tools.config import begin_date, end_date get_projects_lang_code_lines(begin_date, end_date) for t in threads: t.join() old_result = get_projects_lang_code_lines_old(begin_date, end_date) test_results_equal(old_result, project_members_commits_lang_info)

老方法里外層for循環(huán)和內(nèi)層for循環(huán)里均存在耗時(shí)操作：

1）git.get_project_members()

2）git.get_user_info(member_name, debug=False)

分兩步來(lái)優(yōu)化，先里后外或先外后里都行。用多線(xiàn)程替換for循環(huán)，并發(fā)共享外部資源，加鎖避免寫(xiě)沖突。

測(cè)試結(jié)果通過(guò)，函數(shù)運(yùn)行時(shí)間裝飾器顯示（單位秒）：

get_projects_lang_code_lines execution took up time:1.85294

get_projects_lang_code_lines_old execution took up time:108.604177

速度提升了約58倍

以上這篇如何提高python 中for循環(huán)的效率就是小編分享給大家的全部?jī)?nèi)容了，希望能給大家一個(gè)參考，也希望大家多多支持好吧啦網(wǎng)。