Building a retry mechanism in a while loop in python

Question

while true:
    ticker = binance.fetch_ticker("BTC/USDT")
    current_price = ticker['last']
function_A(current_price)

I have a while loop that keeps running to check the current price of Bitcoin every second. Then I also have a function that takes current_price as an input.

However, occasionally, I am getting

"requests.exceptions.ConnectionError: ('Connection aborted.', ConnectionResetError(104, 'Connection reset by peer'))"

So I'm trying to use try, except to make a retry mechanism whenever this error comes up. I've tried this:

while true:
    try_count = 10
    while try_count > 0:
        try:
            ticker = binance.fetch_ticker("BTC/USDT")
            current_price = ticker['last']
            try_count = 0
            break
        except (requests.ConnectionError, requests.ReadTimeout) as error:
            print(error, " detected. Trying again...")
            try_count -= 1
    function_A(current_price)

The problem is that if I do this, current_price ends up being undefined when I plug it in as an input in function_A on the last line. How can I fix this mechanism?

Capybara · Accepted Answer · 2022-06-03 23:07:30Z

1

Defining current_price in a scope outside the second while loop can prevent the problem with current_price sometimes being undefined when calling function_A.

while True:
    current_price = None
    try_count = 10
    while try_count > 0:
        try:
            ticker = binance.fetch_ticker("BTC/USDT")
            current_price = ticker['last']
            try_count = 0
            break
        except (requests.ConnectionError, requests.ReadTimeout) as error:
            print(error, " detected. Trying again...")
            try_count -= 1
    if current_price is not None:
        function_A(current_price)

edited Jun 3, 2022 at 23:07

answered Jun 1, 2022 at 3:35

Capybara

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3 Comments

jy2da Over a year ago

So far, it's working without an error but I'll need to check in later. Thanks for your help! If I had another input for function_A named "amount," would I just add amount = None after the second line? Then say, "if current_price is not None and amount is not None:" for the last if-loop?

Capybara Over a year ago

Yes. That would work

jy2da Over a year ago

Thanks again! I am curious though how this works. What is the point of saying current_price = None in the beginning?

mkjh · Accepted Answer · 2022-06-01 03:35:15Z

0

you may want to explore the backoff library which helps to retry your function. https://pypi.org/project/backoff/

you can just add a backoff decorator on fetch_ticker function and it should retries when it hits RequestException error.

the code should look something like

@backoff.on_exception(backoff.expo, requests.exceptions.RequestException)
def fetch_ticker(ticker):
    # binance.fetch_ticker

answered Jun 1, 2022 at 3:35

mkjh

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1 Comment

jy2da Over a year ago

This looks promising but I'm definitely going to need to search some examples of it being used. Thanks for the pointer!

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