Python中的偏函数

偏函数是从Python2.5引入的一个概念，通过functools模块被用户调用。

偏函数是将所要承载的函数作为partial()函数的第一个参数，原函数的各个参数依次作为partial()函数后续的参数，除非使用关键字参数。

from functools import partial

def func(x, y, z):
    return x + y + z

new_func = partial(func, 10)

print(func(10, 10, 10))  # 30
print(new_func(10, 10))  # 30

应用场景：在Flask的源码里遇过：

request = LocalProxy(partial(_lookup_req_object, 'request'))
session = LocalProxy(partial(_lookup_req_object, 'session'))
g = LocalProxy(partial(_lookup_app_object, 'g'))

Flask中偏函数的思考：

from flask.globals import _request_ctx_stack

class Foo(object):
    def __init__(self):
        self.name = 'lcg'

_request_ctx_stack.push(Foo())

obj = _request_ctx_stack.top
print(obj.name)  # lcg

写成偏函数的形式：

from flask.globals import _request_ctx_stack
from functools import partial

def _lookup_req_object(name):
    top = _request_ctx_stack.top
    if top is None:
        raise RuntimeError('不存在')
    return getattr(top, name)

class Foo(object):
    def __init__(self):
        self.name = 'lcg'
        self.age = 20

req = partial(_lookup_req_object, 'name')
sss = partial(_lookup_req_object, 'age')
_request_ctx_stack.push(Foo())

v = req()
v2 = sss()
print(v)  # lcg
print(v2)  # 20