与 Python 的流畅界面

Question

我有一个 Python 函数“send_message”，它接受三个参数：

send_message("i like windmills", to="INBOX", from="OUTBOX")

我正在考虑在它上面放一个流畅的界面。理想情况下，我想写以下任何内容：

send_message("i like windmills").to("INBOX").from("OUTBOX")

send_message("i like windmills").from("OUTBOX").to("INBOX")

# The `to()` information is mandatory but the `from()` is not (as with real letters), so this one would also be a valid call:
send_message("i like windmills").to("INBOX")

有什么想法可以完成这个或类似的事情吗？

我理解让对象的方法返回“self”的一般方法，但根据我的理解，这会导致这样的事情：

message = Message("i like windmills")
message.to("INBOX").from("OUTBOX").send()

但是这个不如前面的例子好，所以我实际上更喜欢带有命名参数的原始版本。

感谢任何帮助。

Answer 1

可以这样实现，第一次尝试不知道有没有更好的方法。祝你好运！

DEFAULT_SENDER = 'my_address'
#Because the sender object is optional I assume you have a default sender

class Send_message(object):
    def __init__(self, message):
        self.message = message
        self.sender = None
        self.receiver = None
        self.method = None

    def to(self, receiver):
        self.receiver = receiver
        self.method = self.send()
        return self

    def _from(self, sender):
        self.sender = sender
        self.method = self.send()
        return self

    def __call__(self):
        if self.method:
            return self.method()
        return None

    def send(self):
        if self.receiver:
            if not self.sender:
                self.sender = DEFAULT_SENDER

            return lambda:actual_message_code(self.message, self.sender, self.receiver)


def actual_message_code(message, sender, receiver):
    print "Sent '{}' from: {} to {}.".format(message, sender, receiver)



Send_message("Hello")._from('TheLazyScripter').to('samba2')()
Send_message("Hello").to('samba2')._from('TheLazyScripter')()
Send_message("Hello").to('samba2')()

#Only change in actual calling is the trailing ()

通过实施 __call__ 方法，我们可以知道我们何时处于调用链的末尾。这当然会添加尾随 () 调用。并要求您更改指向实际消息传递方法和默认发件人变量的指针，但我认为这是在不知道链何时结束的情况下实现目标的最简单方法。

Answer 2

returning self 有一个缺点。改变其中一个变量会影响另一个变量。这是一个例子

取自@TheLazyScripter 代码，但修改了示例。

a = Send_message("Hello")
b = a
a = a._from('theLazyscripter')
b = b._from('Kracekumar').to('samba 2')
b()
a.message = 'Hello A'
a.to('samba2')()
b.to('samba 2')()
Send_message("Hello").to('samba2')._from('TheLazyScripter')()
Send_message("Hello").to('samba2')()

a和b变量指向同一个实例。修改一个值会影响其他值。查看输出的第二行和第三行。

输出

Sent 'Hello' from: Kracekumar to samba 2.
Sent 'Hello A' from: Kracekumar to samba2.
Sent 'Hello A' from: Kracekumar to samba 2.
Sent 'Hello' from: TheLazyScripter to samba2.
Sent 'Hello' from: my_address to samba2.

b=a 和修改 a 的内容会影响 b 的值。

如何去除这个副作用？

而不是 returning self return 一个新实例来消除副作用。

DEFAULT_SENDER = 'my_address'
#Because the sender object is optional I assume you have a default sender

class Send_message(object):
    def __init__(self, message):
        self.message = message
        self.sender = None
        self.receiver = None
        self.method = None

    def _clone(self):
        inst = self.__class__(message=self.message)
        inst.sender = self.sender
        inst.receiver = self.receiver
        inst.method = self.method
        return inst

    def to(self, receiver):
        self.receiver = receiver
        self.method = self.send()
        return self._clone()

    def _from(self, sender):
        self.sender = sender
        self.method = self.send()
        return self._clone()

    def __call__(self):
        if self.method:
            return self.method()
        return None

    def send(self):
        if self.receiver:
            if not self.sender:
                self.sender = DEFAULT_SENDER

        return lambda:actual_message_code(self.message, self.sender, self.receiver)


def actual_message_code(message, sender, receiver):
    print("Sent '{}' from: {} to {}.".format(message, sender, receiver))



a = Send_message("Hello")
b = a
a = a._from('theLazyscripter')
b = b._from('Kracekumar').to('samba 2')
b()
a.message = 'Hello A'
a.to('samba2')()
b.to('samba 2')()
Send_message("Hello").to('samba2')._from('TheLazyScripter')()
Send_message("Hello").to('samba2')()

_clone 方法每次都会创建实例的新副本。注意：当其中一个值是列表或字典时，需要调用深拷贝。这里是字符串，因此不需要。但是思路还是一样的，复制之前的每个属性returning.

输出

Sent 'Hello' from: Kracekumar to samba 2.
Sent 'Hello A' from: theLazyscripter to samba2.
Sent 'Hello' from: Kracekumar to samba 2.
Sent 'Hello' from: TheLazyScripter to samba2.
Sent 'Hello' from: my_address to samba2.

输出行号 2 和 3 清楚地表明新代码中没有副作用。

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