The module bytecodehack.closure allows the binding of a global reference in a function to a constant reference. It is similar to, but less general than, the attr_freeze module. It has a cuter interface, though.
A toy example:
from bytecodehacks.closure import bind_locals def make_adder(n): def adder(x): return x+n return bind_locals(adder)
Then "make_adder(2)" returns a monadic function that adds 2 to its argument. This can be used to implement parameterized callbacks without using the dreaded `default argument hack' or wrapping the callback in a typing intensive and slow class method.
A more imaginative use is to bind in a mutable object; then state is preserved across calls. This contradicts what the language reference says about code objects, so it's a bit smelly. Never mind, it works (for now). An example, which will be familiar if you have read ``Structure and Interpretation of Computer Programs,'' is:
def make_balance(initial_amount): def withdraw(amount): if current<amount: raise "debt!" else: current=current-amount return current return bind(withdraw,current=[initial_amount])
This can be used as follows:
>>> from bytecodehacks.closure import make_balance >>> W=make_balance(20) >>> W(10) 10 >>> W(4) 6 >>> W(7) Traceback (innermost last): File "<stdin>", line 1, in ? File "/home/mwh21/src/python/bytecodehacks/closure.py", line 98, in withdraw raise "debt!" debt! >>> W(2) 4
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