How to handle a connection error gracefully in requests?

Question

I have a simple python telegram bot, here's the code:

import requests
import json
from time import sleep
import os

filename = 'bot_last_update'
target = open(filename, 'r')
update_from_file = target.read()

# check update from file
update_from_file = update_from_file.strip()
last_update = int(update_from_file)

token = xxxx
url = 'https://api.telegram.org/bot%s/' % token

# We want to keep checking for updates. So this must be a never ending loop
while True:
    # My chat is up and running, I need to maintain it! Get me all chat updates
    get_updates = json.loads(requests.get(url + 'getUpdates').content)
    # Ok, I've got 'em. Let's iterate through each one
    for update in get_updates['result']:
        # First make sure I haven't read this update yet
        if last_update < update['update_id']:
            last_update = update['update_id']
            target = open(filename, 'w')
            target.truncate()
            target.write(str(last_update))
            target.close()
            if update['message']['chat']['type'] == 'private':
            # I've got a new update. Let's see what it is.
                if update['message']['text'] == 'do something':
                    requests.get(url + 'sendMessage', params=dict(chat_id=update['message']['chat']['id'], text='doing it'))
                    os.system('/srv/scripts/do_something.sh')
                    sleep(10)
                    requests.get(url + 'sendMessage', params=dict(chat_id=update['message']['chat']['id'], text='done!'))
                else:
                    pass
    # Let's wait a few seconds for new updates
    sleep(1)

It works fine but every time I have some problem in my network I have this error:

Traceback (most recent call last):
  File "my_telegram_bot.py", line 21, in <module>
    get_updates = json.loads(requests.get(url + 'getUpdates').content)
  File "/usr/local/lib/python2.7/dist-packages/requests/api.py", line 70, in get
    return request('get', url, params=params, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/requests/api.py", line 56, in request
    return session.request(method=method, url=url, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/requests/sessions.py", line 475, in request
    resp = self.send(prep, **send_kwargs)
  File "/usr/local/lib/python2.7/dist-packages/requests/sessions.py", line 596, in send
    r = adapter.send(request, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/requests/adapters.py", line 473, in send
    raise ConnectionError(err, request=request)
requests.exceptions.ConnectionError: ('Connection aborted.', error(113, 'No route to host'))

What would be the best way to avoid that error ? I would like to keep this bot up at all times, so it should not fail in a critical way during those kinds of events (or if it does, it should auto-recover / restart by itself).

Gwen

If you wanted to avoid the error you would need to figure out the issue on network (possibly firewall). If you wanted to handle the error (try to auto-recover), you should look into adding a try/except block. – Geulincx

Answer 1

You need to implement a retry mechanism. Here is an example in python How to retry after exception in python?. A retry mechanism will keep the bot up and avoid the error assuming the connection corrects itself in a reasonable amount of time.

Check out Python requests exception handling for an example of catching your specific exception.

Combining the two examples we get:

from requests import ConnectionError
import requests
import json
import time
import os
connection_timeout = 30 # seconds

...

# My chat is up and running, I need to maintain it! Get me all chat updates
start_time = time.time()
while True:
    try:
        get_updates = json.loads(requests.get(url + 'getUpdates').content)
        break
    except ConnectionError:
        if time.time() > start_time + connection_timeout:
            raise Exception('Unable to get updates after {} seconds of ConnectionErrors'.format(connection_timeout))
        else:
            time.sleep(1) # attempting once every second
# Ok, I've got 'em. Let's iterate through each one

...

This will retry calling getUpdates every second for 30 seconds until the connection rights itself. You can tune the connection_timeout to be as big or small as needed in order to cover the intermittent connection.

Ensor

Answer 2

Similar to answer by @Matt Thomson, This worked for me:

from requests import ConnectionError

try:
    response = fetch_data(**kwargs)
except ConnectionError:
    print(f'Connection timed out. Please check internet connection')

Screwdriver