Use warnings instead of logging exceptions

[ocelotl]

So far we have been catching exceptions we don't want raised and logging a message instead. This definitely accomplishes its purpose and follows these basic error handling principles.

Nevertheless, the specification also takes into consideration that this default behavior can be changed to allow the user strict error handling to reveal bugs.

I suggest that we use the warnings module instead of getLogger(...).exception. In this way, OpenTelemetry can be run in a way that makes the warnings turn into exceptions allowing the user to find bugs more easily while being specification compliant still.

Here are few examples that illustrate how this can work:

#logging_warning.py
from logging import getLogger

_logger = getLogger(__name__)

try:
    1 / 0
except ZeroDivisionError:
    _logger.exception("A division by zero happened")

print("execution complete")

python logging_warning.py

A division by zero happened
Traceback (most recent call last):
  File "logging_warning.py", line 6, in <module>
    1 / 0
ZeroDivisionError: division by zero
execution complete

# raising_warning.py
from warnings import warn

try:
    1 / 0
except ZeroDivisionError:
    warn("A division by zero happened")

print("execution complete")

python raising_warning.py

raising_warning.py:7: UserWarning: A division by zero happened
  warn("A division by zero happened")
execution complete

python -W error raising_warning.py

Traceback (most recent call last):
  File "raising_warning.py", line 5, in <module>
    1 / 0
ZeroDivisionError: division by zero

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "raising_warning.py", line 7, in <module>
    warn("A division by zero happened")
UserWarning: A division by zero happened

[ffe4]

@ocelotl Is this superseded by #1079?

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