extra-context

Sometimes, when you get warnings and exeptions, backtraces are just not enough. For example, you have a loop with 10.000 iterations. In the 1000th iteration there is an exception in a function you called. So you would like to have more context for the error message.

There are 2 options

• give more context at the site the exception occured

• Only possible if you control the exception/warning generation
• Sometimes, there is not enough context to begin with (i.e. you are calling some common utility function)
• Provide additional context as the exception/warning is passed up the call stack

• Can be "opt-in" in user-code, no changes in libraries required.
• Also works for warnings (which normally don't provide backtrace information)

Examples

The main example that inspired writing this library:

to_process = { "file1": {...}, "file2": {...}, ...}

for k, v in to_process.items():
cleaned = clean_data(v)
write_output(k, cleaned)


If there is an exception or warning somewhere in clean_data(v), the "context" i.e. from which file the data came is lost. The backtrace could look something like:

  File "clean.py", line 35, in clean_data
ZeroDivisionError: division by zero


Now, with this library you can give extra context to your error messages

from extra_context import provide_extra_context

to_process = { "file1": {...}, "file2": {...}, ...}

for k, v in to_process.items():
with provide_extra_context(filename=k):
cleaned = clean_data(v)
write_output(k, cleaned)


This would report the same error as:

  File "clean.py", line 35, in clean_data
ZeroDivisionError: division by zero
|- In context: filename='file4'


Decorator

There is also a decorator that reports the function arguments in case of an error

import warnings
from extra_context import provide_call_context

@provide_call_context
def w(x):
warnings.warn("Oops")

w(42)


This reports:

UserWarning: Oops
|- In context: w(42)
warnings.warn("Oops")


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