前言

翻出之前做个压测项，看到locust中对等待时间的实现方式感到好奇，于是总结下来。

源代码实现

def between(min_wait, max_wait):
    """
    Returns a function that will return a random number between min_wait and max_wait.

    Example::

        class MyUser(User):
            # wait between 3.0 and 10.5 seconds after each task
            wait_time = between(3.0, 10.5)
    """
    return lambda instance: min_wait + random.random() * (max_wait - min_wait)


def constant(wait_time):
    """
    Returns a function that just returns the number specified by the wait_time argument

    Example::

        class MyUser(User):
            wait_time = constant(3)
    """
    return lambda instance: wait_time

可以看到locust中对等待时间的处理是先返回一个匿名函数，然后在一个类中 wait_time = constant(3)，再在task类中调用wait_time()返回一个具体的等待时间

def wait(self):
    """
    Make the running user sleep for a duration defined by the Locust.wait_time
    function (or TaskSet.wait_time function if it's been defined).

    The user can also be killed gracefully while it's sleeping, so calling this
    method within a task makes it possible for a user to be killed mid-task, even if you've
    set a stop_timeout. If this behaviour is not desired you should make the user wait using
    gevent.sleep() instead.
    """
    if self.user._state == LOCUST_STATE_STOPPING:
        raise StopUser()
    self.user._state = LOCUST_STATE_WAITING
    self._sleep(self.wait_time())
    if self.user._state == LOCUST_STATE_STOPPING:
        raise StopUser()
    self.user._state = LOCUST_STATE_RUNNING

def _sleep(self, seconds):
    gevent.sleep(seconds)

写法的原理探究

我们先自己仿写一下代码

def call_fuc():
    return lambda x: print(x)
    
class User:
    x = call_fuc()
    
u = User()
u.x()    

看到当我们执行的时候，就会执行返回的匿名函数的逻辑打印一个类对象

拆解函数

对于不熟悉lambda函数的人来说理解这段函数可能有点绕，所以我们拆解一下

def call_fuc():
    # return lambda x: print(x)
    def lam(x):
        print(x)

在上面可以看到返回了一个函数给类属性所以x = call_fuc(),x就成了一个方法了，方法接收一个形参x,接收一个参数x,又是在类里面，这不是就是成了一个实例方法吗，在类里面我们约定俗成把第一个参数叫做self，但是Python本身没有对命名做要求所以在这里x = self。重新定义一个实例方法

class User:
    x = call_fuc()

    def lam(x):
        print(x)

        
u = User()
u.lam()
u.x()  

输出结果