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no-explicit-stacklevel (B028)

Added in v0.0.257 · Related issues · View source

Derived from the flake8-bugbear linter.

Fix is always available.

What it does

Checks for warnings.warn calls without an explicit stacklevel keyword argument.

Why is this bad?

The warnings.warn method uses a stacklevel of 1 by default, which will output a stack frame of the line on which the "warn" method is called. Setting it to a higher number will output a stack frame from higher up the stack.

It's recommended to use a stacklevel of 2 or higher, to give the caller more context about the warning.

Example

import warnings

warnings.warn("This is a warning")

Use instead:

import warnings

warnings.warn("This is a warning", stacklevel=2)

Fix safety

This rule's fix is marked as unsafe because it changes the behavior of the code. Moreover, the fix will assign a stacklevel of 2, while the user may wish to assign a higher stacklevel to address the diagnostic.

References