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docs/ccxt/wiki/examples/py/async-gather-concurrency.md

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+- [Async Gather Concurrency](./examples/py/)
+
+
+ ```python
+ # -*- coding: utf-8 -*-
+
+import asyncio
+import os
+import sys
+
+
+import ccxt.async_support as ccxt  # noqa: E402
+
+
+async def work(exchange_id):
+
+    # create it once per program lifetime
+    exchange = getattr(ccxt, exchange_id)()
+
+    print(exchange_id, 'loaded')
+
+    try:
+
+        # load markets once, first and foremost
+        # https://github.com/ccxt/ccxt/wiki/Manual#loading-markets
+        await exchange.load_markets()
+
+        # use the same exchange instance to iterate over loaded symbols
+        # https://github.com/ccxt/ccxt/wiki/Manual#symbols-and-market-ids
+
+        for symbol in exchange.symbols:
+
+            try:
+
+                # fetch the orderbook for each next symbol
+                orderbook = await exchange.fetch_order_book(symbol)
+
+                # ADD YOUR SUCCESS HANDLING HERE
+                print(exchange_id, 'fetched', symbol, 'orderbook')
+
+            except Exception as e:
+
+                # ADD YOUR ERROR HANDLING HERE
+                # https://github.com/ccxt/ccxt/wiki/Manual#error-handling
+                print(exchange_id, 'could not fetch', symbol, 'orderbook:', type(e).__name__)
+
+    except Exception as e:
+
+        # ADD YOUR ERROR HANDLING HERE
+        print(exchange_id, 'could not load markets:', type(e).__name__)
+
+    # when you're done, don't forget to close the exchange instance properly
+    # otherwise you will get "Unclosed client session" exception
+    await exchange.close()
+
+
+async def main():
+
+    # https://stackoverflow.com/questions/48483348/limited-concurrency-with-asyncio
+    max_concurrency = 5  # how many exchanges at once
+
+    tasks = set()
+    loop = asyncio.get_running_loop()
+    # loop over all exchanges
+    for exchange_id in ccxt.exchanges:
+
+        # wait for some exchange to finish before adding a new one
+        if len(tasks) >= max_concurrency:
+            _done, tasks = await asyncio.wait(tasks, return_when=asyncio.FIRST_COMPLETED)
+        tasks.add(loop.create_task(work(exchange_id)))
+
+    # wait for the remaining exchanges to finish
+    await asyncio.wait(tasks)
+
+
+asyncio.run(main())
+ 
+```