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提高python中for循環(huán)效率的方法

發(fā)布時(shí)間:2020-08-04 09:19:24 來(lái)源:億速云 閱讀:1283 作者:小豬 欄目:開(kāi)發(fā)技術(shù)

這篇文章主要講解了提高python中for循環(huán)效率的方法,內(nèi)容清晰明了,對(duì)此有興趣的小伙伴可以學(xué)習(xí)一下,相信大家閱讀完之后會(huì)有幫助。

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

看完上述內(nèi)容,是不是對(duì)提高python中for循環(huán)效率的方法有進(jìn)一步的了解,如果還想學(xué)習(xí)更多內(nèi)容,歡迎關(guān)注億速云行業(yè)資訊頻道。

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