Computer Science Canada

__python_tricks__

Author:

wtd [ Sun Jul 16, 2006 4:21 pm ]

Post subject:

__python_tricks__

In Python, you can add all kinds of interesting behavior to your classes by defining functions with names like __call__.

code:

>>> class A(object):
... def __call__(self):
... print 42
...
>>> a = A()
>>> a()
42
>>>

How many of these do you know of?

Author:

Null [ Sun Jul 16, 2006 5:41 pm ]

Post subject:

Very well known, but there is also __str__()

code:

class Person(object):
def __init__(self, name, age):
self.name = name
self.age = age

def __str__(self):
return "%s is %s years old" % (self.name, self.age)

person = Person("Joe", 263)
print person

Author:

wtd [ Sun Jul 16, 2006 6:07 pm ]

Post subject:

Null wrote:

Very well known, but there is also __str__()

I see your __str__ and raise you a __repr__.

code:

>>> class A(object):
... def __repr__(self):
... return "Hello world"
...
>>> A()
Hello world
>>>

Author:

Null [ Sun Jul 16, 2006 9:36 pm ]

Post subject:

__iter__() and __len__()

code:

class LinkedList(object):
class Node(object):
def __init__(self, data):
self.data = data
self.next = None

def __init__(self, data_list):
self.first = self.Node(data_list[0])
self.__size = 0
self.current = self.first

for data in data_list[2:]:
self.append(data)

def last(self):
current = self.first

while current.next is not None:
current = current.next

return current

def append(self, data):
self.__size += 1

self.last().next = self.Node(data)

def __len__(self):
return self.__size

def __iter__(self):
return self

def next(self):
try:
if not self.current:
raise StopIteration

result = self.current.data
self.current = self.current.next
return result

except StopIteration:
self.current = self.first
raise StopIteration

if __name__ == "__main__":
linked_list = LinkedList(range(1, 11))

for node in linked_list:
print node

I love Ruby, I really do. Its consistency, blocks, and pure design. My problem with it is that obscure-ness (is that a word?) in code seems to be preferred, and it starts to look extremely cryptic. I'm starting to lean towards Python, especially when it comes to readability. I'm still deciding which I prefer.

Author:	rizzix [ Mon Jul 17, 2006 4:29 pm ]
Post subject:
One of the reasons I dont like python is because of these special __methods__. What an ugly naming convention.

Author:	Cervantes [ Mon Jul 17, 2006 4:32 pm ]
Post subject:
They don't look so bad. They are effective at drawing your attention to them. And so your attention should be drawn to them, as they are special.

Author:	rizzix [ Mon Jul 17, 2006 4:36 pm ]
Post subject:
I would hardly call __str__, __len__, __iter__, etc, special. Instead of __init__ they could have simply defined a method called self. Since "self" is used to refer to "this" object, having a method my the name self can safely act as a constructor for "this" object. (basically lots of things can be done a lot better without the ugly convention)

Author:	McKenzie [ Wed Jul 19, 2006 10:18 am ]
Post subject:
So you like using compareTo in Java? Try __lt__(self, other) in Python. Called when < is used. I like this because I miss the good old operator overloading from C.

Author:	wtd [ Wed Jul 19, 2006 10:51 am ]
Post subject:
McKenzie wrote: I like this because I miss the good old operator overloading from C. I hope you mean C++.

Author:	McKenzie [ Wed Jul 19, 2006 10:36 pm ]
Post subject:
, I actually typed C on purpose. I didn't think about it that much. I recalled learning about operator overloading about 12-14 years ago. I didn't do much C++ back then, so I assumed this was C knowledge.

Author:	wtd [ Thu Jul 20, 2006 9:15 pm ]
Post subject:
No problem. The compatibilities between the two have made it really hard to push the idea that they're distinct languages.

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