根据列表中的值在 Python 中调用不同的函数

Question

我有一个脚本，它将指标列表作为输入，然后从数据库中获取这些指标以执行各种操作。

我的问题是不同的客户端获得不同的指标子集，但我不想每次添加新客户端时都编写新的 IF 块。所以现在，我有一个大的 IF 块，它根据相应的指标是否在列表中来调用不同的函数。处理这个问题的最优雅或 Pythonic 方式是什么？

设置和功能定义：

clientOne = ['churn','penetration','bounce']
clientTwo = ['engagement','bounce']

def calcChurn(clientId):
    churn = cursor.execute(sql to get churn)
    [...]
    return churn

def calcEngagement(clientId):
    engagement = cursor.execute(sql to get engagement)
    [...]
    return engagement

以类似的格式想象其他三个函数，因此每个唯一指标对应一个函数。现在这是脚本中获取指标列表的代码块：

def scriptName(client, clientId):
    if churn in client:
        churn = calcChurn(clientId)
    if engagement in client:
        engagement = calcEngagement(clientId)
    if penetration in client:
    [...]

Answer 1

也许将所需的调用封装在一个对象中可能是有意义的。

如果您的客户成为对象是有意义的，特别是如果许多客户调用同一组函数来获取指标，那么您可以创建一组 Client 子类，它们调用一组预定义的函数来获取指标。

比映射字典重一点。

''' Stand alone functions for sql commands.
    These definitions however dont really do anything.
'''


def calc_churn(clientId):
    return 'result for calc_churn'


def calc_engagement(clientId):
    return 'result for calc_engagement'


''' Client base object '''


class Client(object):
    ''' Base object allows list of functions
    to be stored in client subclasses'''

    def __init__(self, id):
        self.id = id
        self.metrics = []
        self.args = []

    def add_metrics(self, metrics, *args):
        self.metrics.extend(metrics)
        self.args = args

    def execute_metrics(self):
        return {m.__name__: m(*self.args) for m in self.metrics}


''' Specific sub classes '''


class Client1(Client):

    def __init__(self, id):
        ''' define which methods are called for this class'''

        super(Client1, self).__init__(id)
        self.add_metrics([calc_churn], id)


class Client2(Client):

    def __init__(self, id):
        ''' define which methods are called for this class'''

        super(Client2, self).__init__(id)
        self.add_metrics([calc_churn, calc_engagement], id)


''' create client objects and  '''

c1 = Client1(1)
c2 = Client2(2)

for client in [c1, c2]:
    print client.execute_metrics()

您将从execute_metrics 获得的结果是dict 将函数名称映射到该客户端的结果。

Answer 2

您可以使用静态方法创建一个类并使用getattr 来获取正确的方法。这类似于 mgilson 的建议，但您基本上可以免费获得 dict 创建：

class Calculators:

    @staticmethod
    def calcChurn():
        print("called calcChurn")

    @staticmethod
    def calcEngagement():
        print("called calcEngagement")

    @staticmethod
    def calcPenetration():
        print("called calcPenetration")

stats = ["churn", "engagement", "penetration", "churn", "churn", "engagement", "undefined"]

def capitalise(str):
    return str[0].upper() + str[1:]

for stat in stats:
    try:
        getattr(Calculators, "calc" + capitalise(stat))()
    except AttributeError as e:
        print("Unknown statistic: " + stat)

称为 calcChurn
称为 calcEngagement
称为 calcPenetration
称为 calcChurn
称为 calcChurn
称为 calcEngagement
未知统计：未定义

Answer 3

通常，您会创建名称到函数的映射，并使用它来计算您想要的东西：

client_action_map = {
  'churn': calcChurn,
  'engagement': calcEngagement,
  ...
}

def scriptName(actions, clientId):
    results = {}
    for action in actions:
        results[action] = client_action_map[action](clientId)
    return results