A python library for dropping stack frames.
This can be useful for removing decorators from stack traces, when using a framework with a lot of decorators.
Let's us write a small decorator for measuring the time it takes to call a function:
from time import perf_counter
def measure_time(func):
def wrapper(*args, **kwargs):
before = perf_counter()
result = func(*args, **kwargs)
after = perf_counter()
print(f"{func.__name__} took {after - before}s.")
return result
return wrapperWe can use it like this:
@measure_time
def foo(should_raise):
assert not should_raise
return 42
@measure_time
def bar(should_raise):
return foo(should_raise)
@measure_time
def baz(should_raise):
return bar(should_raise)
baz(False)On my computer this prints:
foo took 2.2800122678745538e-07s.
bar took 3.576500057533849e-05s.
baz took 4.227000135870185e-05s.
Great. But what happens if we raise an error?
baz(True)yields:
Traceback (most recent call last):
File "example.py", line 32, in <module>
baz(True)
File "example.py", line 7, in wrapper
result = func(*args, **kwargs)
File "example.py", line 28, in baz
return bar(should_raise)
File "example.py", line 7, in wrapper
result = func(*args, **kwargs)
File "example.py", line 23, in bar
return foo(should_raise)
File "example.py", line 7, in wrapper
result = func(*args, **kwargs)
File "example.py", line 17, in foo
assert not should_raise
AssertionError
Notice how every other line is the wrapper from our decorator? If we have large codebase and it is
using a framework with a lot of decorators, this can make the stack traces hard to read, because
most of the frames are irrelevant decorators.
We can use the dropstackframe library to rewrite our decorator:
from time import perf_counter
from dropstackframe import drop_stack_frame
def measure_time(func):
def wrapper(*args, **kwargs):
before = perf_counter()
try:
result = func(*args, **kwargs)
except Exception:
drop_stack_frame()
raise
after = perf_counter()
print(f"{func.__name__} took {after - before}s.")
return result
return wrapperNow, if we get an error:
baz(True)we get:
Traceback (most recent call last):
File "example2.py", line 37, in <module>
baz(True)
File "example2.py", line 33, in baz
return bar(should_raise)
File "example2.py", line 28, in bar
return foo(should_raise)
File "example2.py", line 22, in foo
assert not should_raise
AssertionError
and all the annoying wrapper stack frames have been removed.
Let's say you have a large codebase that uses dropstackframe and one day you have a bug that is
really hard to find. In fact you start suspecting that the bug might be hidden by
drop_stack_frame. You can use set_enable_drop_stack_frame to disable drop_stack_frame:
from dropstackframe import set_enable_drop_stack_frame
set_enable_drop_stack_frame(False)
baz(True)set_enable_drop_stack_frame can also be used as a context manager, if you only want to disable
drop_stack_frame in a limited region of your code:
from dropstackframe import set_enable_drop_stack_frame
with set_enable_drop_stack_frame(False):
baz(True)![github-actions[bot] avatar](https://avatars.githubusercontent.com/in/15368?v=4 "github-actions[bot]")
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