updated more ch. 17 examples to Python 3.7

17-futures-py3.7/countries/flags_threadpool.py

@@ -0,0 +1,71 @@
+"""Download flags of top 20 countries by population
+
+ThreadPoolExecutor version
+
+Sample run::
+
+    $ python3 flags_threadpool.py 
+    DE FR BD CN EG RU IN TR VN ID JP BR NG MX PK ET PH CD US IR 
+    20 flags downloaded in 0.35s
+
+"""
+# BEGIN FLAGS_THREADPOOL
+import os
+import time
+import sys
+from concurrent import futures  # <1>
+
+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 = 'downloads/'
+
+MAX_WORKERS = 20  # <2>
+
+def save_flag(img, filename):
+    path = os.path.join(DEST_DIR, filename)
+    with open(path, 'wb') as fp:
+        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 download_one(cc):  # <3>
+    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))  # <4>
+    with futures.ThreadPoolExecutor(workers) as executor:  # <5>
+        res = executor.map(download_one, sorted(cc_list))  # <6>
+
+    return len(list(res))  # <7>
+
+
+def main():  # <10>
+    t0 = time.time()
+    count = download_many(POP20_CC)
+    elapsed = time.time() - t0
+    msg = '\n{} flags downloaded in {:.2f}s'
+    print(msg.format(count, elapsed))
+
+
+if __name__ == '__main__':
+    main()
+# END FLAGS_THREADPOOL