python 网络下载的三种风格 未完成

import osimport timeimport sys

import requests#依序下载POP20_CC = ('CN IN US ID BR PK NG BD RU JP'            'MX PH VN ET EG DE IR TE CD TR').split()BASE_URL = 'http://flupy.org/data/flags'DEST_DIR = 'downloads/'

def save_flag(img, filename):    path = os.path.join(DEST_DIR, filename)    if not os.path.isdir(DEST_DIR):        os.mkdir(DEST_DIR)

    with open(path, 'wb') as fp:        if fp.writable():            fp.write(img)

def get_flag(cc):#下载内容    url = '{}/{cc}/{cc}.gif'.format(BASE_URL, cc=cc.lower())  # 格式化字符串{BASE_URL}/{cc}/{cc}    print(url)    resp = requests.get(url)#以二进制形式下载    return resp.content#返回二进制数据

def show(text):    print(text,end=' ')    sys.stdout.flush()#在liunx系统下，不加这句，打印时间不是立刻打印的。假如在windows中不存在这个问题（正常情况遇到换行才会刷新stdout缓冲）

def download_many(cc_list):    for cc in sorted(cc_list):#sorted()这个排序的结果和作用是什么？        image=get_flag(cc)        show(cc)

        save_flag(image,cc.lower()+'.gif')    return len(cc_list)

def main_n(download_many):    t1=time.time()    count=download_many(POP20_CC)    elapsed=time.time()-t1    msg='\n{} flags download in {:.2f}s'    print(msg.format(count,elapsed))

if __name__ == '__main__':    main_n(download_many)#BD BR CD CN DE EG ET ID IN IR JPMX NG PH PK RU TE TR US VN# 19 flags download in 8.57s

#concurrent.futures 模块下载

from concurrent import futuresimport osimport timeimport requestsimport sys

MAX_WORKERS = 20POP20_CC = ('CN IN US ID BR PK NG BD RU JP'            'MX PH VN ET EG DE IR TE CD TR').split()BASE_URL = 'http://flupy.org/data/flags'DEST_DIR = 'downloads/'

def save_flag(img, filename):    path = os.path.join(DEST_DIR, filename)    if not os.path.isdir(DEST_DIR):        os.mkdir(DEST_DIR)

    with open(path, 'wb') as fp:        if fp.writable():            fp.write(img)

def get_flag(cc):    url = '{}/{cc}/{cc}.gif'.format(BASE_URL, cc=cc.lower())    resp = requests.get(url)    return resp.content

def show(text):    print(text, end=' ')    sys.stdout.flush()

def main_n(download_many):    t1 = time.time()    count = download_many(POP20_CC)    elapsed = time.time() - t1    msg = '\n{} flags download in {:.2f}s'    print(msg.format(count, elapsed))

def download_one(cc):    image = get_flag(cc)    show(cc)    save_flag(image, cc.lower() + '.gif')    return cc

def download_many(cc_list):    workers = min(MAX_WORKERS, len(cc_list))  # 设置最大线程数

    with futures.ThreadPoolExecutor(workers) as executor:        res = executor.map(download_one, sorted(cc_list))    return len(list(res))

# BD BR CN ID EG JPMX IN NG RU TE ET CD IR PH PK VN DE US TR# 19 flags download in 2.44sif __name__ == '__main__':    main_n(download_many)