如何提高python 中for循環(huán)的效率
對(duì)于某個(gè)城市的出租車數(shù)據(jù),一天就有33210000條記錄,如何將每輛車的數(shù)據(jù)單獨(dú)拎出來(lái)放到一個(gè)專屬的文件中呢?
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):
我之前的做法類似這樣:
words = ['apple', 'bananan', 'cake', 'dumpling']
for word in words:
print word
并行for循環(huán)類似這樣:
from multiprocessing.dummy import Pool as ThreadPool items = 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 time
from multiprocessing.dummy import Pool as ThreadPool
def 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_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):
"""
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)用多線程替代for循環(huán)
并發(fā)訪問(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_time
def 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:
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):
"""
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
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