Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Welcome To Ask or Share your Answers For Others

Categories

0 votes
410 views
in Technique[技术] by (71.8m points)

python 3.x - How can I use an operator to compose functions?

It's fairly straightforward to write a function that composes two other functions. (For simplicity, assume they are one parameter each.)

def compose(f, g):
    fg = lambda x: f(g(x))
    return fg

def add1(x):
    return x + 1

def add2(x):
    return x + 2

print(compose(add1, add2)(5))  # => 8

I would like to do composition using an operator, e.g., (add1 . add2)(5).

Is there a way to do that?

I tried various decorator formulations, but I couldn't get any of them to work.

def composable(f):
  """
    Nothing I tried worked. I won't clutter up the question 
    with my failed attempts.
  """

@composable
def add1(x):
    return x + 1
See Question&Answers more detail:os

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
Welcome To Ask or Share your Answers For Others

1 Reply

0 votes
by (71.8m points)

First only a certain amount of operator symbols are allowed in Python syntax. Dot "." is not a valid operator.

This page (the page is actually about the Python operator module, but the naming convention are the same to datamodel and the content is more organized) listed all available operators and the corresponding instance methods. For example, if you want to use "@" as the operator, you can write a decorator like this:

import functools

class Composable:

    def __init__(self, func):
        self.func = func
        functools.update_wrapper(self, func)

    def __matmul__(self, other):
        return lambda *args, **kw: self.func(other.func(*args, **kw))

    def __call__(self, *args, **kw):
        return self.func(*args, **kw)

To test:

@Composable
def add1(x):
    return x + 1

@Composable
def add2(x):
    return x + 2

print((add1 @ add2)(5))
# 8

与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…
OGeek|极客中国-欢迎来到极客的世界,一个免费开放的程序员编程交流平台!开放,进步,分享!让技术改变生活,让极客改变未来! Welcome to OGeek Q&A Community for programmer and developer-Open, Learning and Share
Click Here to Ask a Question

...