Develop Reference

Understanding how a try except logic works within two while loops

I'm having trouble understanding the mechanism of my code. I want to retrieve the realtime price data of a crypto from an exchange and print it every second, while creating a retry mechanism that catches an exception when it occurs.
while True:
try_cnt = 10
while try_cnt > 0:
try:
price = get_current_price(symbol) # function imported from elsewhere
print(price)
time.sleep(1)
try_cnt = 0
break
except Exception as e:
print(e)
try_cnt -= 1
This is how I have it set up but I'm having trouble follow the logic. This is how I see it as of now. After the code has been run:
Price is retrieved
try_cnt is set to 0 and the second while loop is broken
The next second, try_cnt is reset to 10 and price is retrieved
try_cnt is set to 0 again and the second while loop is broken
repeat of this process
Am I understanding this correctly?
EDIT: the reason why I have a while loop outside is that I have other things that are going on at specific times besides the part I mentioned here. The part that I mentioned is supposed to be running all the time every second. For example,
while True:
if now.hour == 0 and now.minute == 0 and now.second == 0:
A = functionA(x,y)
try_cnt = 10
while try_cnt > 0:
try:
price = get_current_price(symbol) # function imported from elsewhere
print(price)
time.sleep(1)
try_cnt = 0
break
except Exception as e:
print(e)
try_cnt -= 1

I think that you are understanding everything just fine, but the code itself is a little silly and redundant. For example, setting try_cnt to 0 and then following that with break is pointless - both lines do the same thing. And unless there is some significance to the variable try_cnt that is not present within the code you posted, its existence seems pretty much useless to me. Here's code that does the exact same thing as the code above, but without the redundancies:
while True:
try:
price = get_current_price(symbol)
print(price)
time.sleep(1)
except Exception as e:
print(e)
In response to your edit, the while True loop encompassing everything makes a lot more sense. However, this means that your code isn't doing what you want it to do. The outer while loop ensures that even if try_cnt reaches 0, try_cnt will just be reset to 10 on the next pass and it will be as if no Exceptions ever occurred (besides the ten error messages in the console). If you want that inner while loop to stop executing when ten Exceptions occur, you need to place the try_cnt = 10 statement outside of both while loops like so:
try_cnt = 10
while True:
if now.hour == 0 and now.minute == 0 and now.second == 0:
A = functionA(x,y)
while try_cnt > 0:
try:
price = get_current_price(symbol)
print(price)
time.sleep(1)
try_cnt = 10
break
except Exception as e:
print(e)
try_cnt -= 1

How to repeat a step in a loop if an action fails?

In the case I am looping into a list, where for value msg_list = 0 it will execute action(0), usr). This action can fail for a determined user, I should choose aother user if it happens, perform all the actions related to the user
How can I do to repeat action[0] if it fails?
for msg in range(len(msg_list)):
# in this case msg = 0
usr = select_random_user()
multiple_actions_for(usr) # This are lots of code lines I don't want to repeat!!
try:
action(msg, usr)
more_actions(usr.related_stuff)
except Exception as e:
go_back_to(msg =0 instead of looping into msg=1) # this is what I want to do
How can I do to get that? Repeat the loop for msg = i instead of passing to msg = i + 1?

Put your code into the endless while-loop with exiting from it if try was successful:
for msg in range(len(msg_list)):
while True:
usr = select_random_user()
multiple_actions_for(usr)
try:
action(msg, usr)
more_actions(usr.related_stuff)
except Exception as e:
continue
else:
break

It really depends. Is it okay to go back to the beginning of the loop? If so, you can call "continue", which stops the current iteration, and restarts the loop. Otherwise, I don't think there's something similar to a goto in Python, no. It's a very structured language.

Try using while loop instead of for loop. The idea is as shown bellow:
bool still_looping = True
msg = 0
while still_looping:
usr = select_random_user()
multiple_actions_for(usr)
try:
action(msg, usr)
more_actions(usr.related_stuff)
if (msg < len (msg_list)):
msg += 1
except Exception as e:
# Do whatever you want here. msg was not incremented
if (msg == len(msg_list))
still_looping = False #verify if this was the last execution

Python - How to loop until site is down using requests and threads

So what I want to do is that I want to make a sorts of monitor a website that pick ups a random number. Before it does it needs to requests to the website to see whenever it is valid or not. When it is live it will generate random numbers 1-100 and I want it to check every random 3-6 second and then print again the number and repeat until the website is down.
What I have tried to do is following:
def get_product_feed(url_site):
thread = url_site
password = False #We start by giving a false/true value
while not password: #If it is not True then we do the for loop
available = False
while not available:
try:
checkpass = requests.get(thread, timeout=12) #We requests the site to see if its alive or not
if ('deadsite' in checkpass.url): #If it contains etc deadsite then we enter the while True
while True:
contcheck = requests.get(thread,timeout=12) #We make new requests to see if its dead.
if ('deadsite' in contcheck.url): #if it is, then we sleep 3-7sec and try again
randomtime = random.randint(3, 7)
time.sleep(randomtime)
else: #If its not containig it anymore then we send the bs4 value
available = True
bs4 = soup(contcheck.text, 'lxml')
return bs4
break
else: #If its having either of them then we send instant.
bs4 = soup(contcheck.text, 'lxml')
return bs4
break
except Exception as err:
randomtime = random.randint(1, 2)
time.sleep(randomtime)
continue
def get_info(thread):
while True:
try:
url = thread
resp = requests.get(url, timeout=12) #We requests to the website here
resp.raise_for_status()
json_resp = resp.json() #We grab the json value.
except Exception as err:
randomtime = random.randint(1,3)
time.sleep(randomtime)
continue
metadata = json_resp['number'] #We return the metadata value back to get_identifier
return metadata
def get_identifier(thread):
new = get_info(thread) #We requests the get_info(thread):
try:
thread_number = new
except KeyError:
thread_number = None
identifier = ('{}').format(thread_number) #We return back to script
return identifier
def script():
url_site = 'https://www.randomsitenumbergenerator.com/' #What url we gonna use
old_list = []
while True:
for thread in get_product_feed(url_site): #We loop to see through get_product_feed if its alive or not
if get_identifier(thread) not in old_list: # We then ask get_identifier(thread) for the values and see if its in the old_list or not.
print(get_identifier(thread)
old_list.append(get_identifier(thread)
I added a comment to make it easier to understand what is going on.
The issue I am having now that I am not able to make get_identifier(thread) to run until the website is down and I want it to continue to print out until the website is live til it dies and that is my question! What do I need to do to make it happen?
My thoughts was to add eventually threads maybe that 10 threads are checking at the same time to see if the website is dead or not and give back the value as a print but I am not sure if that is my solution for the question.

Python - how to get updated link that was passed as an argument?

I'm passing a link as an argument in a thread, that I want to scrape the timestamp on. But in the function that the thread is pointing to, the timestamp value does not change, every time i'm rescraping it. How do you get timeLink to be dynamic and change every time it goes over the while loop? Here is the code:
def abcStart(timeLink):
while True:
res = timeLink
res.raise_for_status()
timestamp = BeautifulSoup(res.content, 'html.parser').find_all('b')
if timestamp[0].text == otherTimestamp[0].text:
work on something
break
if timestamp[0].text > otherTimestamp[0].text:
continue
else:
print('not yet')
time.sleep(30)
break
timelink = requests.get('http://example.com/somelink')
threadobj = threading.Thread(target=abcStart, args=(timelink))
threadobj.start()
threadobj.join()

It looks like there is only one http request being sent. On this line:
timelink = requests.get('http://example.com/somelink')
the abcStart() function is receiving the http response, and using that one value the whole time it is running. This will cause us to scrape the same page every time. If we want to have a different page to scrape for each loop iteration, we need to perform another http request each time. Something like this:
def abcStart(timeLink):
while True:
res = requests.get(timeLink) # send request here
res.raise_for_status()
timestamp = BeautifulSoup(res.content, 'html.parser').find_all('b')
if timestamp[0].text == otherTimestamp[0].text:
work on something
break
if timestamp[0].text > otherTimestamp[0].text:
continue
else:
print('not yet')
time.sleep(30)
break
timeLink = 'http://example.com/somelink' # declare url
threadobj = threading.Thread(target=abcStart, args=(timelink))
threadobj.start()
threadobj.join()

I guess you should move timeLink request inside your function:
def abcStart(timeLink):
while True:
res = requests.get('http://example.com/somelink')
res.raise_for_status()
timestamp = BeautifulSoup(res.content, 'html.parser').find_all('b')
if timestamp[0].text == otherTimestamp[0].text:
work on something
break
if timestamp[0].text > otherTimestamp[0].text:
continue
else:
print('not yet')
time.sleep(30)
break
threadobj = threading.Thread(target=abcStart, args=())
threadobj.start()
threadobj.join()

Calling a function within a function within a class

So there's this website that posts something I want to buy at a random time of day for a limited amount of time and I want to write something to send a message to my phone when a new url is posted to that webpage.
I planned on doing this by counting the number of links on the page (since it's rarely updated) and checking it every 5 minutes against what it was 5 minutes before that, then 5 minutes later check it against what it was 10 minutes before that, 5 minutes later check what it was 15 minutes before that... and if it's greater than what it originally was, send a message to my phone. Here's what I have so far:
class url_alert:
url = ''
def link_count(self):
notifyy=True
while notifyy:
try:
page = urllib.request.urlopen(self.url)
soup = bs(page, "lxml")
links=[]
for link in soup.findAll('a'):
links.append(link.get('href'))
notifyy=False
print('found', int(len(links)), 'links')
except:
print('Stop making so many requests')
time.sleep(60*5)
return len(links)
def phone(self):
self= phone
phone.message = client.messages.create(to="", from_="",body="")
print('notified')
def looper(self):
first_count = self.link_count()
print('outside while')
noty = True
while noty:
try:
second_count = self.link_count()
print('before compare')
if second_count == first_count:
self.phone()
noty = False
except:
print('not quite...')
time.sleep(60)
alert = url_alert()
alert.looper()
As a test, I decided to set the if statement that determines whether or not to send a message as equal but the loop kept on running. Am I calling the functions within the looper function the right way?

It looks like you need to eliminate the try block, as it is now, if self.phone() takes an exception you will never leave the loop
def looper(self):
first_count = self.link_count()
while True:
if first_count != self.link_count():
self.phone()
break
time.sleep(60)