什么是一个干净,python方式有多个构造函数在Python? [英] What is a clean, pythonic way to have multiple constructors in Python?
问题描述
我找不到这个的确切答案。 AFAIK,在Python类中不能有多个 __ init __
函数。那么什么是解决这个问题的好办法呢?
假设我有一个名为 Cheese
的类,其中包含 number_of_holes
属性。如何用两种方法创建奶酪对象...
- 一个需要多个孔的方法:
parmesan = Cheese(num_holes = 15)
- 一个没有参数,只是随机化
number_of_holes
属性:gouda = Cheese()
一个方法来做到这一点,但这似乎很笨拙:
class Cheese():
pre>
def __init __(self, num_holes = 0):
if(num_holes == 0):
#randomize number_of_holes
else:
number_of_holes = num_holes
你说什么?有更好的方法吗?
解决方案实际上
None
magicvalues:class Cheese():
def __init __(self,num_holes = None):
如果num_holes是无:
...
现在如果你想完全自由添加更多参数:
class Cheese():
def __init __(self,* args,** kwargs):
#args - 匿名参数的元组
#kwargs - 命名参数的字典
self.num_holes = kwargs.get('num_holes',random_holes())
为了更好地解释
* args
和** kwargs
(你可以改变这些名字):def f ** kwargs):
print'args:',args,'kwargs:',kwargs
>>> f('a')
args:('a',)kwargs:{}
>>> f(ar ='a')
args:()kwargs:{'ar':'a'}
>>> f(1,2,param = 3)
args:(1,2)kwargs:{'param':3}
http://docs.python.org/reference /expressions.html#calls
I can't find a definitive answer for this. AFAIK, you can't have multiple
__init__
functions in a Python class. So what is a good way to solve this problem?Suppose I have an class called
Cheese
with thenumber_of_holes
property. How can I have two ways of creating cheese-objects...
- one that takes a number of holes like this:
parmesan = Cheese(num_holes = 15)
- and one that takes no arguments and just randomizes the
number_of_holes
property:gouda = Cheese()
I can think of only one way to do this, but that seems kinda clunky:
class Cheese():
def __init__(self, num_holes = 0):
if (num_holes == 0):
# randomize number_of_holes
else:
number_of_holes = num_holes
What do you say? Is there a better way?
Actually None
is much better for "magic" values:
class Cheese():
def __init__(self, num_holes = None):
if num_holes is None:
...
Now if you want complete freedom of adding more parameters:
class Cheese():
def __init__(self, *args, **kwargs):
#args -- tuple of anonymous arguments
#kwargs -- dictionary of named arguments
self.num_holes = kwargs.get('num_holes',random_holes())
To better explain the concept of *args
and **kwargs
(you can actually change these names):
def f(*args, **kwargs):
print 'args: ', args, ' kwargs: ', kwargs
>>> f('a')
args: ('a',) kwargs: {}
>>> f(ar='a')
args: () kwargs: {'ar': 'a'}
>>> f(1,2,param=3)
args: (1, 2) kwargs: {'param': 3}
http://docs.python.org/reference/expressions.html#calls
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