我知道Python不支持方法重载,但我遇到了一个问题,我似乎无法用Python的好方法来解决。

我正在创造一款角色需要射击各种子弹的游戏,但是我该如何编写不同的函数去创造这些子弹呢?例如,假设我有一个函数,它创建了一颗以给定速度从a点飞到B点的子弹。我会这样写一个函数:

def add_bullet(sprite, start, headto, speed):
    # Code ...

但我想写其他函数来创建项目符号,比如:

def add_bullet(sprite, start, direction, speed):
def add_bullet(sprite, start, headto, spead, acceleration):
def add_bullet(sprite, script): # For bullets that are controlled by a script
def add_bullet(sprite, curve, speed): # for bullets with curved paths
# And so on ...

等等,有很多变化。有没有更好的方法不用这么多关键字参数,因为它很快就会变得很难看。重命名每个函数也很糟糕,因为你得到的不是add_bullet1、add_bullet2就是add_bullet_with_really_long_name。

以下是一些问题的答案:

不,我不能创建一个子弹类层次结构,因为那太慢了。管理项目符号的实际代码是用C编写的,我的函数是围绕C API的包装器。 我知道关键字参数,但检查各种参数组合是令人讨厌的,但默认参数帮助分配,如加速度=0


当前回答

对于函数重载,可以使用“自己动手”的解决方案。下面这个摘自Guido van Rossum关于多方法的文章(因为在Python中,多方法和重载之间几乎没有区别):

registry = {}

class MultiMethod(object):
    def __init__(self, name):
        self.name = name
        self.typemap = {}
    def __call__(self, *args):
        types = tuple(arg.__class__ for arg in args) # a generator expression!
        function = self.typemap.get(types)
        if function is None:
            raise TypeError("no match")
        return function(*args)
    def register(self, types, function):
        if types in self.typemap:
            raise TypeError("duplicate registration")
        self.typemap[types] = function


def multimethod(*types):
    def register(function):
        name = function.__name__
        mm = registry.get(name)
        if mm is None:
            mm = registry[name] = MultiMethod(name)
        mm.register(types, function)
        return mm
    return register

它的用法是

from multimethods import multimethod
import unittest

# 'overload' makes more sense in this case
overload = multimethod

class Sprite(object):
    pass

class Point(object):
    pass

class Curve(object):
    pass

@overload(Sprite, Point, Direction, int)
def add_bullet(sprite, start, direction, speed):
    # ...

@overload(Sprite, Point, Point, int, int)
def add_bullet(sprite, start, headto, speed, acceleration):
    # ...

@overload(Sprite, str)
def add_bullet(sprite, script):
    # ...

@overload(Sprite, Curve, speed)
def add_bullet(sprite, curve, speed):
    # ...

目前最严格的限制是:

不支持方法,只支持非类成员的函数; 继承没有被处理; 不支持Kwargs; 注册新函数应该在导入时完成,这是不线程安全的

其他回答

在Python中重载方法是很棘手的。但是,可以使用传递字典、列表或原始变量的方法。

我已经为我的用例尝试了一些东西,这可以帮助理解人们重载方法。

让我们以你为例:

类重载方法调用不同类的方法。

def add_bullet(sprite=None, start=None, headto=None, spead=None, acceleration=None):

从远程类传递参数:

add_bullet(sprite = 'test', start=Yes,headto={'lat':10.6666,'long':10.6666},accelaration=10.6}

Or

add_bullet(sprite = 'test', start=Yes, headto={'lat':10.6666,'long':10.6666},speed=['10','20,'30']}

因此,从方法重载中实现对列表、字典或基本变量的处理。

为您的代码尝试一下。

Python在呈现方法时支持“方法重载”。事实上,你刚刚描述的东西在Python中实现起来很简单,有很多不同的方式,但我认为:

class Character(object):
    # your character __init__ and other methods go here

    def add_bullet(self, sprite=default, start=default, 
                 direction=default, speed=default, accel=default, 
                  curve=default):
        # do stuff with your arguments

在上面的代码中,default是这些参数的一个合理的默认值,即None。然后,您可以只使用感兴趣的参数调用该方法,Python将使用默认值。

你也可以这样做:

class Character(object):
    # your character __init__ and other methods go here

    def add_bullet(self, **kwargs):
        # here you can unpack kwargs as (key, values) and
        # do stuff with them, and use some global dictionary
        # to provide default values and ensure that ``key``
        # is a valid argument...

        # do stuff with your arguments

另一种替代方法是直接将所需函数直接挂钩到类或实例:

def some_implementation(self, arg1, arg2, arg3):
  # implementation
my_class.add_bullet = some_implementation_of_add_bullet

还有一种方法是使用抽象工厂模式:

class Character(object):
   def __init__(self, bfactory, *args, **kwargs):
       self.bfactory = bfactory
   def add_bullet(self):
       sprite = self.bfactory.sprite()
       speed = self.bfactory.speed()
       # do stuff with your sprite and speed

class pretty_and_fast_factory(object):
    def sprite(self):
       return pretty_sprite
    def speed(self):
       return 10000000000.0

my_character = Character(pretty_and_fast_factory(), a1, a2, kw1=v1, kw2=v2)
my_character.add_bullet() # uses pretty_and_fast_factory

# now, if you have another factory called "ugly_and_slow_factory" 
# you can change it at runtime in python by issuing
my_character.bfactory = ugly_and_slow_factory()

# In the last example you can see abstract factory and "method
# overloading" (as you call it) in action 

根据定义,在python中重载函数是不可能的(详细信息请阅读下文),但您可以使用简单的装饰器实现类似的功能

class overload:
    def __init__(self, f):
        self.cases = {}

    def args(self, *args):
        def store_function(f):
            self.cases[tuple(args)] = f
            return self
        return store_function

    def __call__(self, *args):
        function = self.cases[tuple(type(arg) for arg in args)]
        return function(*args)

你可以这样用

@overload
def f():
    pass

@f.args(int, int)
def f(x, y):
    print('two integers')

@f.args(float)
def f(x):
    print('one float')


f(5.5)
f(1, 2)

修改它以适应您的用例。

概念的澄清

function dispatch: there are multiple functions with the same name. Which one should be called? two strategies static/compile-time dispatch (aka. "overloading"). decide which function to call based on the compile-time type of the arguments. In all dynamic languages, there is no compile-time type, so overloading is impossible by definition dynamic/run-time dispatch: decide which function to call based on the runtime type of the arguments. This is what all OOP languages do: multiple classes have the same methods, and the language decides which one to call based on the type of self/this argument. However, most languages only do it for the this argument only. The above decorator extends the idea to multiple parameters.

为了澄清这一点,假设我们用一种假想的静态语言定义函数

void f(Integer x):
    print('integer called')

void f(Float x):
    print('float called')

void f(Number x):
    print('number called')


Number x = new Integer('5')
f(x)
x = new Number('3.14')
f(x)

使用静态分派(重载),您将看到“number被调用”两次,因为x已被声明为number,这就是重载所关心的。在动态分派中,你会看到“integer called, float called”,因为它们是函数被调用时x的实际类型。

你可以很容易地在Python中实现函数重载。下面是一个使用浮点数和整数的例子:

class OverloadedFunction:
    def __init__(self):
        self.router = {int : self.f_int   ,
                       float: self.f_float}
    
    def __call__(self, x):
        return self.router[type(x)](x)
    
    def f_int(self, x):
        print('Integer Function')
        return x**2
    
    def f_float(self, x):
        print('Float Function (Overloaded)')
        return x**3

# f is our overloaded function
f = OverloadedFunction()

print(f(3 ))
print(f(3.))

# Output:
# Integer Function
# 9
# Float Function (Overloaded)
# 27.0

代码背后的主要思想是,类包含您想要实现的不同(重载)函数,而Dictionary则作为路由器,根据输入类型(x)将代码指向正确的函数。

PS1。对于自定义类,如Bullet1,可以按照类似的模式初始化内部字典,如self。D = {Bullet1: self。f_Bullet1…}。代码的其余部分是相同的。

PS2。所提出的解决方案的时间/空间复杂度也相当好,每个操作的平均成本为O(1)。

通过传递关键字args。

def add_bullet(**kwargs):
    #check for the arguments listed above and do the proper things