如果签名只在参数数量上有所不同，那么使用默认参数是正确的方法。如果您希望能够传入不同类型的参数，我会尽量避免在另一个回答中提到的基于isinstance的方法，而是使用关键字参数。

如果只使用关键字参数变得笨拙，您可以将其与类方法结合使用(bzrlib代码喜欢这种方法)。这只是一个愚蠢的例子，但我希望你能明白:

class C(object):

    def __init__(self, fd):
        # Assume fd is a file-like object.
        self.fd = fd

    @classmethod
    def from_filename(cls, name):
        return cls(open(name, 'rb'))

# Now you can do:
c = C(fd)
# or:
c = C.from_filename('a filename')

注意，所有这些类方法仍然要经过相同的__init__，但使用类方法比记住__init__的关键字参数组合要方便得多。

isinstance is best avoided because Python's duck typing makes it hard to figure out what kind of object was actually passed in. For example: if you want to take either a filename or a file-like object you cannot use isinstance(arg, file), because there are many file-like objects that do not subclass file (like the ones returned from urllib, or StringIO, or...). It's usually a better idea to just have the caller tell you explicitly what kind of object was meant, by using different keyword arguments.

与Java不同，您不能定义多个构造函数。但是，如果没有传递一个默认值，则可以定义一个默认值。

def __init__(self, city="Berlin"):
  self.city = city

如果签名只在参数数量上有所不同，那么使用默认参数是正确的方法。如果您希望能够传入不同类型的参数，我会尽量避免在另一个回答中提到的基于isinstance的方法，而是使用关键字参数。

如果只使用关键字参数变得笨拙，您可以将其与类方法结合使用(bzrlib代码喜欢这种方法)。这只是一个愚蠢的例子，但我希望你能明白:

class C(object):

    def __init__(self, fd):
        # Assume fd is a file-like object.
        self.fd = fd

    @classmethod
    def from_filename(cls, name):
        return cls(open(name, 'rb'))

# Now you can do:
c = C(fd)
# or:
c = C.from_filename('a filename')

注意，所有这些类方法仍然要经过相同的__init__，但使用类方法比记住__init__的关键字参数组合要方便得多。

isinstance is best avoided because Python's duck typing makes it hard to figure out what kind of object was actually passed in. For example: if you want to take either a filename or a file-like object you cannot use isinstance(arg, file), because there are many file-like objects that do not subclass file (like the ones returned from urllib, or StringIO, or...). It's usually a better idea to just have the caller tell you explicitly what kind of object was meant, by using different keyword arguments.

最简单的方法是通过关键字参数:

class City():
  def __init__(self, city=None):
    pass

someCity = City(city="Berlin")

这是非常基本的东西。也许可以看看Python文档?

对于你给出的例子，使用默认值:

class City:
    def __init__(self, name="Default City Name"):
        ...
    ...

一般来说，你有两个选择:

根据类型执行if-elif块: 定义__init__(self, name): 如果isinstance(name, str): #待办事项 elif isinstance(name, City) #待办事项 #待办事项 使用鸭子类型——也就是说，假设类的用户足够聪明，能够正确地使用它。这通常是首选的选项。

杰克的回答是正确的。这样做:

>>> class City:
...     def __init__(self, city=None):
...         self.city = city
...     def __repr__(self):
...         if self.city:  return self.city
...         return ''
...
>>> c = City('Berlin')
>>> print c
Berlin
>>> c = City()
>>> print c

>>>