This snippet defines a simple decorator to post-process a function's return value through a sequence of filters. As a first application, the decorator can transform a generator function into a function returning a sequence type (list, tuple, dict).
Post-process generated values with a decorator.
# python >= 2.6
from __future__ import print_function
from functools import update_wrapper
def post_process(*filters):
"""Decorator to post process a function's return value through a
sequence of filters (functions with a single argument).
Example:
@post_process(f1, f2, f3)
def f(*args, **kwd):
...
return value
then calling f(...) will actually return f3( f2( f1( f(...)))).
This can also be used to convert a generator to a function
returning a sequence type:
@post_process(dict)
def my_generator():
...
yield key, value
"""
def decorate(func):
def wrapper(*args, **kwd):
rv = func(*args, **kwd)
for f in filters:
rv = f(rv)
return rv
update_wrapper(wrapper, func)
return wrapper
return decorate
@post_process(dict)
def stones(n):
while n > 1:
x = (3 * n + 1) // 2 if n % 2 else n // 2
yield n, x
n = x
@post_process(list)
def fibo(n):
a, b = 0, 1
for i in range(n):
yield a
a, b = b, a + b
@post_process(list, reversed, list)
def squares(n):
for i in range(n):
yield i * i
if __name__ == "__main__":
print("stones", stones(11))
print("fibo", fibo(12))
print("squares", squares(10))
""" my output -->
stones {2: 1, 4: 2, 5: 8, 8: 4, 10: 5, 11: 17, 13: 20, 17: 26, 20: 10, 26: 13}
fibo [0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89]
squares [81, 64, 49, 36, 25, 16, 9, 4, 1, 0]
"""
Gribouillis 1,391 Programming Explorer Team Colleague
How to transform such a generator into a function returning a tuple of all items
from itertools import chain
@post_process(chain.from_iterable, tuple)
def runme():
yield (1, 2)
yield (i + 3 for i in range(4))
yield [7, 8]
print(runme())
""" my output -->
(1, 2, 3, 4, 5, 6, 7, 8)
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