Day 75: Understanding errors in Python3

Errors

understand errors python

I wrote about python error handling a few days ago.

And a Python beginner came to me

Explained his dilemma.

That person didn’t understand the errors at all and didn’t know how to interprete them.

And this is kind of a big deal.

Interpreting errors

So today, we’ll talk about understanding errors to start with.

And then the critical thinking behind correcting them.

I’ll make it easy!

We got an error message thrown by python

Traceback (most recent call last):
  File "/analyst_client.py", line 19, in <module>
    ca.main()
  File "/alkoanalyst.py", line 476, in main
    self.__check_archived_orders()
  File "/alkoanalyst.py", line 349, in __check_archived_orders
    content = self.__api.archived_orders(pair_slash)
  File "/alkoanalyst.py", line 89, in archived_orders
    return self.api_call('archived_orders', {}, 1, couple)
  File "/newapi.py", line 59, in api_call
    answer = self.__post(url, param)  # Post Request
  File "/newapi.py", line 46, in __post
    page = urllib.request.urlopen(req).read()
  File "/usr/lib/python3.9/urllib/request.py", line 214, in urlopen
    return opener.open(url, data, timeout)
  File "/usr/lib/python3.9/urllib/request.py", line 523, in open
    response = meth(req, response)
  File "/usr/lib/python3.9/urllib/request.py", line 632, in http_response
    response = self.parent.error(
  File "/usr/lib/python3.9/urllib/request.py", line 561, in error
    return self._call_chain(*args)
  File "/usr/lib/python3.9/urllib/request.py", line 494, in _call_chain
    result = func(*args)
  File "/usr/lib/python3.9/urllib/request.py", line 641, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 502: Bad Gateway

1. Actual error = bottom

  File "/usr/lib/python3.9/urllib/request.py", line 641, in http_error_default
    raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 502: Bad Gateway

  • 1st line: we can see that the error lies in the request.py, which is the python urllib module

  • 2nd line: That module is raising an HTTPError, with the parameters i fed into it.

These are my actual parameter names.

  • 3rd line: And the actual error is an HTTP Error 502 : Bad gateway

Notes

  • Since the actual issue is an HTTP error and the error code is a 502.

  • I can already say that 100% this is a server error See why?

  • So I already know that, I’m not dealing with server problems properly.

  • As if there is a problem with the server, my program shouldn’t crash like that.

2. Let’s keep reading from this from top to bottom.

We’ll split the rest of the error to make it easier to understand

Upper block –> Furthest module from the error

  • This is the last module that was executed

  • And we should not worry about this

  • This part is just directing us to where the issue is.

  • It’s the higher up module in my program.

Traceback (most recent call last):
  File "/analyst_client.py", line 19, in <module>
    ca.main()
Upper Intermediate block –> Leads us to the error

  • This is one of the classes that I made

  • It contains the api_call that was made using the class in the error block below

     File "/alkoanalyst.py", line 476, in main
 self.__check_archived_orders()
  File "/alkoanalyst.py", line 349, in __check_archived_orders
 content = self.__api.archived_orders(pair_slash)
  File "/alkoanalyst.py", line 89, in archived_orders
 return self.api_call('archived_orders', {}, 1, couple)
Intermediate block –> The actual code we have to modify <–

  • This is a module for making API calls

  • Since it’s closer to the actual python module error at the bottom.

  • It contains the code that I will have to modify !

      File "/newapi.py", line 59, in api_call
answer = self.__post(url, param)  # Post Request
  File "/newapi.py", line 46, in __post
Lower Intermediate block –> python library that raised the error

  • In this block we’re still saying that the reported error concerns

  • The urllib library, request module so it’s linked to the error

     page = urllib.request.urlopen(req).read()
  File "/usr/lib/python3.9/urllib/request.py", line 214, in urlopen
 return opener.open(url, data, timeout)
  File "/usr/lib/python3.9/urllib/request.py", line 523, in open
 response = meth(req, response)
  File "/usr/lib/python3.9/urllib/request.py", line 632, in http_response
 response = self.parent.error(
  File "/usr/lib/python3.9/urllib/request.py", line 561, in error
 return self._call_chain(*args)
  File "/usr/lib/python3.9/urllib/request.py", line 494, in _call_chain
 result = func(*args)
    Lower Block –> Actual error !
      #--> ACTUAL ERROR <--
  File "/usr/lib/python3.9/urllib/request.py", line 641, in http_error_default
 raise HTTPError(req.full_url, code, msg, hdrs, fp)
urllib.error.HTTPError: HTTP Error 502: Bad Gateway

Conclusion

  • The upper part leads us to the error

  • The Intermediate part is the code we need to modify

  • The lower part is the actual error that was raisde by the module.

This is a simplified methodology to understand errors.

But in all this the most important part is to understand the error.

\ Codarren /

Written on March 16, 2021