Traceback format_exc failing with ConnectionError

[Phyks]

Hi,

I tried to use a script using requests (v2.18.1) on a remote website without having any internet connectivity. Of course, this resulted in a long stack traces due to the absence of internet connectivity, as expected, which ended up with

requests.exceptions.ConnectionError: HTTPSConnectionPool(host='updates.weboob.org', port=443): Max retries exceeded with url: /1.3/main/modules.list (Caused by NewConnectionError('<urllib3.connection.VerifiedHTTPSConnection object at 0x7fe5f7474be0>: Failed to establish a new connection: [Errno -2] Name or service not known',))

Problem is that I catch any such exception and pass them to traceback.format_exc in order to have a nice error formatting in my logs.

Expected Result

Using something like

try:
    my_code_calling_requests()
except Exception as e:
            log.error(("Unknown exception raised: %s" % traceback.format_exc(e)))

I would have expected a nicely formatted exception in my logs.

Actual Result

Actually, it raised another exception, which I am not 100% sure to understand :/ Full traceback is:

Traceback (most recent call last):
  File "MY_CODE", line 363, in <module>
    traceback.format_exc(e)),
  File "/usr/lib/python3.6/traceback.py", line 163, in format_exc
    return "".join(format_exception(*sys.exc_info(), limit=limit, chain=chain))
  File "/usr/lib/python3.6/traceback.py", line 117, in format_exception
    type(value), value, tb, limit=limit).format(chain=chain))
  File "/usr/lib/python3.6/traceback.py", line 486, in __init__
    _seen=_seen)
  File "/usr/lib/python3.6/traceback.py", line 486, in __init__
    _seen=_seen)
  File "/usr/lib/python3.6/traceback.py", line 486, in __init__
    _seen=_seen)
  File "/usr/lib/python3.6/traceback.py", line 497, in __init__
    capture_locals=capture_locals)
  File "/usr/lib/python3.6/traceback.py", line 332, in extract
    if limit >= 0:
TypeError: '>=' not supported between instances of 'ConnectionError' and 'int'

System Information

{
  "chardet": {
    "version": "3.0.4"
  },
  "cryptography": {
    "version": "1.9"
  },
  "implementation": {
    "name": "CPython",
    "version": "3.6.1"
  },
  "platform": {
    "release": "4.11.7-1-ARCH",
    "system": "Linux"
  },
  "pyOpenSSL": {
    "openssl_version": "1010006f",
    "version": "17.0.0"
  },
  "requests": {
    "version": "2.18.1"
  },
  "system_ssl": {
    "version": "1010006f"
  },
  "urllib3": {
    "version": "1.21.1"
  },
  "using_pyopenssl": true
}

Thanks!

[Lukasa]

The first argument of format_exc is not the exception to print, it's a limit on how many lines of trace back to print. You may want to reread the documentation for the function on python.org. The correct call is just format_exc.

[Phyks]

Oops, truly sorry about this :/ I took it from a snippet and should have checked the snippet thoroughly :/