CSC/ECE 517 Spring 2014/ch1 1w1l m

Design Patterns Involving Closures

Background

What is a closure?

Very simply, a closure is a function that can use a reference to a variable that was valid within the scope that the closure was defined, but need not be in-scope where the closure is called. A quick example is very illustrative.

>>> def closure_builder():
...     message = "String, in-scope where closure is defined"
...     def closure(new_msg=None):
...         if new_msg is None:
...             print message
...         else:
...             print new_msg
...     return closure
... 
>>> default_closure = closure_builder()
>>> del closure_builder  # Without closures, the message var would be gone now
>>> default_closure()  # But it's still here!
String, in-scope where closure is defined
>>> default_closure("I can do this too, although it's bit obvious")
I can do this too, although it's bit obvious

References

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