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You can see that the default arguments are stored in a tuple which is an attribute of the function in question. This actually has nothing to do with the class in question and goes for any function.
The __init__ method is the Python equivalent of the C++ constructor in an object-oriented approach. The __init__ function is called every time an object is created from a class. The __init__ method lets the class initialize the object's attributes and serves no other purpose. It is only used within classes.
In Python the __init__() method is called the constructor and is always called when an object is created. Types of constructors : default constructor: The default constructor is a simple constructor which doesn't accept any arguments.
Providing Multiple Constructors With @classmethod in Python. A powerful technique for providing multiple constructors in Python is to use @classmethod . This decorator allows you to turn a regular method into a class method. Unlike regular methods, class methods don't take the current instance, self , as an argument.
Mutable default arguments don't generally do what you want. Instead, try this:
class Node:
def __init__(self, wordList=None, adjacencyList=None):
if wordList is None:
self.wordList = []
else:
self.wordList = wordList
if adjacencyList is None:
self.adjacencyList = []
else:
self.adjacencyList = adjacencyList
Let's illustrate what's happening here:
Python 3.1.2 (r312:79147, Sep 27 2010, 09:45:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> class Foo:
... def __init__(self, x=[]):
... x.append(1)
...
>>> Foo.__init__.__defaults__
([],)
>>> f = Foo()
>>> Foo.__init__.__defaults__
([1],)
>>> f2 = Foo()
>>> Foo.__init__.__defaults__
([1, 1],)
You can see that the default arguments are stored in a tuple which is an attribute of the function in question. This actually has nothing to do with the class in question and goes for any function. In python 2, the attribute will be func.func_defaults.
As other posters have pointed out, you probably want to use None as a sentinel value and give each instance it's own list.
class Node:
def __init__(self, wordList=None adjacencyList=None):
self.wordList = wordList or []
self.adjacencyList = adjacencyList or []
I would try:
self.wordList = list(wordList)
to force it to make a copy instead of referencing the same object.
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