python中for循环加速_如何提高python 中for循环的效率[通俗易懂]

对于某个城市的出租车数据，一天就有33210000条记录，如何将每辆车的数据单独拎出来放到一个专属的文件中呢？

思路很简单：

就是循环33210000条记录，将每辆车的数据搬运到它该去的文件中。

但是对于3000多万条数据，一个一个循环太消耗时间，我花了2个小时才搬运了60万数据，算算3000万我需要花费100个小时，也就需要4-5天。并且还需要保证这五天全天开机，不能出现卡机的事故。

因此，需要使用并行进行for循环的技巧：

由于3000万数据放到csv中导致csv打不开，因此我就把一个csv通过split软件将其切分成每份60万，共53个csv。

我原来的思路是读取文件夹，获取由每一个60万的csv文件组成的列表，再分别对每一个60万的csv进行处理。实质上还是循环33210000次，并行for循环就是同时处理几个60万的csv文件，就能成倍的减少时间消耗。

并行进行for循环是受下面的方法启发：

我之前的做法类似这样：

words = [“apple”, “bananan”, “cake”, “dumpling”]

for word in words:

print word

并行for循环类似这样：

from multiprocessing.dummy import Pool as ThreadPool

items = list()

pool = ThreadPool()

pool.map(process, items)

pool.close()

pool.join()

其中,process是进行处理的函数

实例代码如下：

# -*- coding: utf-8 -*-

import time

from multiprocessing.dummy import Pool as ThreadPool

def process(item):

print(“正在并行for循环”)

print(item)

time.sleep(5)

items = [“apple”, “bananan”, “cake”, “dumpling”]

pool = ThreadPool()

pool.map(process, items)

pool.close()

pool.join()

补充知识：Python3用多线程替代for循环提升程序运行速度

优化前后新老代码如下：

from git_tools.git_tool import get_collect_projects, QQNews_Git

from threading import Thread, Lock

import datetime

base_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_time

def 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_time

def get_projects_lang_code_lines(begin_date, end_date):

“””

获取项目代码行语言相关统计――新方法(提升效率)

应用多线程替代for循环

并发访问共享外部资源

: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_time

def get_projects_lang_code_lines_old(begin_date, end_date):

“””

获取项目代码行语言相关统计――老方法(耗时严重)

使用最基本的思路进行编程

双层for循环嵌套并且每层都包含耗时操作

: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:

continue

user_commits_lang_info_dict[member_name] = user_commits_lang_info

project_members_commits_lang_info[git.project] = user_commits_lang_info_dict

except:

pass

return project_members_commits_lang_info

def test_results_equal(resultA, resultB):

“””

测试方法

: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)

老方法里外层for循环和内层for循环里均存在耗时操作：

1)git.get_project_members()

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

分两步来优化，先里后外或先外后里都行。用多线程替换for循环，并发共享外部资源，加锁避免写冲突。

测试结果通过，函数运行时间装饰器显示(单位秒)：

get_projects_lang_code_lines execution took up time:1.85294

get_projects_lang_code_lines_old execution took up time:108.604177

速度提升了约58倍

以上这篇如何提高python 中for循环的效率就是小编分享给大家的全部内容了，希望能给大家一个参考，也希望大家多多支持云海天教程。