Skipping execution of -with- block

Question

I am defining a context manager class and I would like to be able to skip the block of code without raising an exception if certain conditions are met during instantiation.

Answer 1

Based on @Peter's answer, here's a version that uses no string manipulations but should work the same way otherwise:

from contextlib import contextmanager

@contextmanager
def skippable_context(skip):
    skip_error = ValueError("Skipping Context Exception")
    prev_entered = getattr(skippable_context, "entered", False)
    skippable_context.entered = False

    def command():
        skippable_context.entered = True
        if skip:
            raise skip_error

    try:
        yield command
    except ValueError as err:
        if err != skip_error:
            raise
    finally:
        assert skippable_context.entered, "Need to call returned command at least once."
        skippable_context.entered = prev_entered


print("=== Running with skip disabled ===")
with skippable_context(skip=False) as command:
    command()
    print("Entering this block")
print("... Done")

print("=== Running with skip enabled ===")
with skippable_context(skip=True) as command:
    command()
    raise NotImplementedError("... But this will never be printed")
print("... Done")