# Implementation 1: not portable
import sys
def fn(gen):
"""Turns a generator expression into a callable."""
def anonymous(*args):
return gen.next()
return anonymous
def args():
"""Works with fn(); yields args passed to anonymous()."""
while True:
# Stack frame will look like:
# anonymous(args=(...)) "foo(3,4,5)"
# gen.next() "return gen.next()"
# args.next() internal genexp code
yield sys._getframe(2).f_locals['args']
args = args()
foo = fn(a + b * c for (a,b,c) in args)
assert foo(3,4,5) == 3+4*5
assert foo(4,5,6) == 4+5*6
# Implementation 2: not thread-safe (but it could be)
class SingleElementIterator:
"""Iterator that must be constantly fed by assigning to .value"""
def __iter__(self):
return self
def next(self):
value = self.value
del self.value
return value
args2 = SingleElementIterator()
def fn2(gen):
"""Turns a generator expression into a callable."""
def anonymous(*args_):
args2.value = args_
return gen.next()
return anonymous
foo = fn2(a + b * c for (a,b,c) in args2)
assert foo(3,4,5) == 3+4*5
assert foo(4,5,6) == 4+5*6
