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@sttts
Created November 27, 2014 00:44
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Add optional parameters to a Python generator
# Add optional parameters to a decorator.
#
# Usage:
#
# Start with a normal decorator without parameters, e.g.
#
# def decorator(f):
# ...
#
# Add additional parameters with default value and use @optionally_parametrized_decorator, e.g.
#
# @optionally_parametrized_decorator
# def decorator(f, x=42, y=7):
# ...
#
# Then you can use the resulting decorator without _and_ with parameters, e.g.
#
# @decorator
# def f(a, b, c):
# ...
#
# @decorator(x=1, y=2)
# def f(a, b, c):
# ...
#
def optionally_parametrized_decorator(orig_decorator):
def decorator_or_decorator_func(orig_handler=None, **decorator_kwargs):
def decorator_wrap(orig_handler):
return orig_decorator(orig_handler, **decorator_kwargs)
# Python decorator magic: when orig_handler!=None is passed, we know
# that the decorator was called without parameters, i.e. like @with_valid_from_header.
# If the decorator is used as with_valid_from_header(min_api_version=2), then
# python will call this function without direct orig_handler parameter, but only with the
# min_api_version.
if orig_handler:
return decorator_wrap(orig_handler)
else:
return decorator_wrap
return decorator_or_decorator_func
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