Implement simple polling server that updates files in shared memory

api.py

-import requests
+#!/usr/bin/env python
+import sys
+import os
+import atexit
+import time
+import grequests
+from Queue import PriorityQueue
 
-class APIError(RuntimeError):
-    pass
+interval = 3        # poll exchange tickers every 3 seconds
+cap_interval = 60   # poll check market cap every minute
 
-def get_check_status(errstr, url, *args):
-    r = requests.get(url, timeout=10.0, *args)
-    if r.status_code != 200:
-        raise APIError(errstr)
-    return r.json()
+exchanges = {
+    'https://btc-e.com/api/3/ticker/btc_usd':
+        ('btce', ('btc_usd', 'last'), 'USD', interval),
+    'https://api.gdax.com/products/BTC-USD/ticker':
+        ('coinbase', ('price',), 'USD', interval),
+    'https://www.bitstamp.net/api/v2/ticker/btcusd/':
+        ('bitstamp', ('last',), 'USD', interval),
+    'https://api.bitfinex.com/v1/pubticker/btcusd':
+        ('bitfinex', ('last_price',), 'USD', interval),
+    'https://data.btcchina.com/data/ticker?market=btccny':
+        ('btcchina', ('ticker', 'last'), 'CNY', interval),
+    'http://api.huobi.com/staticmarket/ticker_btc_json.js':
+        ('huobi', ('ticker', 'last'), 'CNY', interval),
+    'https://www.okcoin.com/api/v1/ticker.do?symbol=btc_usd':
+        ('okcoin', ('ticker', 'last'), 'CNY', interval),
+    'https://api.kraken.com/0/public/Ticker?pair=XXBTZEUR':
+        ('kraken', ('result', 'XXBTZEUR', 'c', 0), 'EUR', interval),
+    'https://api.coinmarketcap.com/v1/ticker/bitcoin/':
+        ('coinmarketcap', (0, 'market_cap_usd'), 'USD', cap_interval),
+}
 
-def poll_btce():
-    url = 'https://btc-e.com/api/3/ticker/btc_usd'
-    return float(get_check_status('BTC-e', url)['btc_usd']['last']), 'USD'
+queue = PriorityQueue(len(exchanges))
 
-def poll_coinbase():
-    url = 'https://api.gdax.com/products/BTC-USD/ticker'
-    return float(get_check_status('Coinbase', url)['price']), 'USD'
+def generate_requests():
+    while True:
+        scheduled, url = queue.get()
+        wait = scheduled - time.time()
 
-def poll_bitstamp():
-    url = 'https://www.bitstamp.net/api/v2/ticker/btcusd/'
-    return float(get_check_status('Bitstamp', url)['last']), 'USD'
+        if wait > 0:
+            time.sleep(wait)
 
-def poll_bitfinex():
-    url = 'https://api.bitfinex.com/v1/pubticker/btcusd'
-    return float(get_check_status('Bitfinex', url)['last_price']), 'USD'
+        yield grequests.get(url, timeout=5)
 
-def poll_btcchina():
-    url = 'https://data.btcchina.com/data/ticker?market=btccny'
-    return float(get_check_status('BTCChina', url)['ticker']['last']), 'CNY'
+if __name__ == '__main__':
+    for url in exchanges.iterkeys():
+        queue.put((0, url))
 
-def poll_huobi():
-    url = 'http://api.huobi.com/staticmarket/ticker_btc_json.js'
-    return float(get_check_status('Huobi', url)['ticker']['last']), 'CNY'
+    root = sys.argv[1] if len(sys.argv) == 2 else '/dev/shm/tothemoon'
+    create_root = not os.path.isdir(root)
 
-def poll_okcoin():
-    url = 'https://www.okcoin.com/api/v1/ticker.do?symbol=btc_usd'
-    return float(get_check_status('OKcoin', url)['ticker']['last']), 'CNY'
+    def remove_files():
+        for ex in exchanges.itervalues():
+            path = root + '/' + ex[0]
+            if os.path.exists(path):
+                os.remove(path)
 
-def poll_kraken():
-    url = 'https://api.kraken.com/0/public/Ticker?pair=XXBTZEUR'
-    return float(get_check_status('Kraken', url)['result']['XXBTZEUR']['c'][0]), 'EUR'
+        if create_root:
+            os.rmdir(root)
 
-def poll_coinmarketcap():
-    url = 'https://api.coinmarketcap.com/v1/ticker/bitcoin'
-    return get_check_status('Coinmarketcap', url)[0]['market_cap_usd'], 'USD'
+    atexit.register(remove_files)
 
-if __name__ == '__main__':
-    print 'btc-e', poll_btce()
-    print 'coinbase', poll_coinbase()
-    print 'bitstamp', poll_bitstamp()
-    print 'bitfinex', poll_bitfinex()
-    print 'btcchina', poll_btcchina()
-    print 'huobi', poll_huobi()
-    print 'okcoin', poll_okcoin()
-    print 'kraken', poll_kraken()
-    print 'coinmarketcap', poll_coinmarketcap()
+    if create_root:
+        try:
+            os.mkdir(root)
+        except OSError as e:
+            print >>sys.stderr, 'Could not create root directory %s:' % root,
+            print >>sys.stderr, e.strerror
+            sys.exit(1)
+
+    try:
+        for res in grequests.imap(generate_requests()):
+            exid, indices, currency, interval = exchanges[res.request.url]
+            queue.put((time.time() + interval, res.request.url))
+
+            last = res.json()
+            for i in indices:
+                last = last[i]
+            last = float(last)
+
+            with open(root + '/' + exid, 'w') as f:
+                print >>f, last, currency
+    except KeyboardInterrupt:
+        pass