some chapter 17 examples updated for Python 3.7

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

@@ -0,0 +1,72 @@
+"""Download flags of top 20 countries by population
+
+asyncio + aiottp version
+
+Sample run::
+
+    $ python3 flags_asyncio.py 
+    CN EG BR IN ID RU NG VN JP DE TR PK FR ET MX PH US IR CD BD 
+    20 flags downloaded in 0.35s
+
+"""
+# BEGIN FLAGS_ASYNCIO
+import os
+import time
+import sys
+import asyncio  # <1>
+
+import aiohttp  # <2>
+
+
+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/'
+
+
+def save_flag(img, filename):
+    path = os.path.join(DEST_DIR, filename)
+    with open(path, 'wb') as fp:
+        fp.write(img)
+
+
+async def get_flag(session, cc):  # <3>
+    url = '{}/{cc}/{cc}.gif'.format(BASE_URL, cc=cc.lower())
+    async with session.get(url) as resp:        # <4>
+        return await resp.read()  # <5>
+
+
+def show(text):
+    print(text, end=' ')
+    sys.stdout.flush()
+
+
+async def download_one(session, cc):  # <6>
+    image = await get_flag(session, cc)  # <7>
+    show(cc)
+    save_flag(image, cc.lower() + '.gif')
+    return cc
+
+
+async def download_many(cc_list):
+    async with aiohttp.ClientSession() as session:  # <8>
+        res = await asyncio.gather(                 # <9>
+            *[asyncio.create_task(download_one(session, cc))
+                for cc in sorted(cc_list)])
+
+    return len(res)
+
+
+def main():  # <10>
+    t0 = time.time()
+    count = asyncio.run(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_ASYNCIO