python使用期物处理并发教程【python基础】

目录

• 1. futures.ThreadPoolExecutor
• 2. 期物
• 3. 阻塞型I/O和GIL
• 4. 使用concurrent.futures模块启动进程

import os
import time
import sys
import requests
POP20_CC = ("CN IN US ID BR PK NG BD RU JP " "MX PH VN ET EG DE IR TR CD FR").split()
BASE_URL = "http://flupy.org/data/flags"
DEST_DIR = "./"
def save_flag(img, filename):  # 保存图像
    path = os.path.join(DEST_DIR, filename)
    with open(path, "wb") as fp:
        fp.write(img)
def get_flag(cc):  # 获取图像
    url = "{}/{cc}/{cc}.gif".format(BASE_URL, cc=cc.lower())
    resp = requests.get(url)
    return resp.content
def show(text):  # 打印信息
    print(text, end=" ")
    sys.stdout.flush()
def download_many(cc_list):
    for cc in sorted(cc_list):
        image = get_flag(cc)  # 获取
        show(cc)  # 打印
        save_flag(image, cc.lower() + ".gif")  # 保存
    return len(cc_list)
def main(download_many):
    t0 = time.time()
    count = download_many(POP20_CC)
    elapsed = time.time() - t0
    msg = "
{} flags downloaded in {:.2f}s"
    print(msg.format(count, elapsed))  # 计时信息
# ----使用 futures.ThreadPoolExecutor 类实现多线程下载
from concurrent import futures
MAX_WORKERS = 20  # 最多使用几个线程
def download_one(cc):
    image = get_flag(cc)
    show(cc)
    save_flag(image, cc.lower() + ".gif")
    return cc
def download_many_1(cc_list):
    workers = min(MAX_WORKERS, len(cc_list))
    with futures.ThreadPoolExecutor(workers) as executor:
        #  使用工作的线程数实例化 ThreadPoolExecutor 类；
        #  executor.__exit__ 方法会调用 executor.shutdown(wait=True) 方法，
        #  它会在所有线程都执行完毕 前阻塞线程
        res = executor.map(download_one, sorted(cc_list))
        # download_one 函数 会在多个线程中并发调用；
        # map 方法返回一个生成器，因此可以迭代， 获取各个函数返回的值
    return len(list(res))
if __name__ == "__main__":
    # main(download_many) # 24 秒
    main(download_many_1)  # 3 秒

def download_many_2(cc_list):
    cc_list = cc_list[:5]
    with futures.ThreadPoolExecutor(max_workers=3) as executor:
        to_do = []
        for cc in sorted(cc_list):
            future = executor.submit(download_one, cc)
            # executor.submit 方法排定可调用对象的执行时间，
            # 然后返回一个 期物，表示这个待执行的操作
            to_do.append(future) # 存储各个期物
            msg = "Scheduled for {}: {}"
            print(msg.format(cc, future))
        results = []
        for future in futures.as_completed(to_do):
            # as_completed 函数在期物运行结束后产出期物
            res = future.result() # 获取期物的结果
            msg = "{} result: {!r}"
            print(msg.format(future, res))
            results.append(res)
    return len(results)

输出：
Scheduled for BR: 
Scheduled for CN: 
Scheduled for ID: 
Scheduled for IN: 
Scheduled for US: 
CN  result: "CN"
BR  result: "BR"
ID  result: "ID"
IN  result: "IN"
US  result: "US"
5 flags downloaded in 3.20s