what is def __init__?

[ateale]

Hey guys

on my quest to learn python I keep coming across:
def __init__

I think I understand it is defining a method called "init" - but what's with all the underscores. Or is it some builtin method of Python?

Sorry - confused

Cheers!

[ilikepython]

Hey guys

on my quest to learn python I keep coming across:
def __init__

I think I understand it is defining a method called "init" - but what's with all the underscores. Or is it some builtin method of Python?

Sorry - confused

Cheers!

__init__ is the function that is called automatically upon an object's construction:
[code=python]
class Test:
def __init__(self, num): # called when object is constructed
self.value = num

def getVal(self):
return self.value

obj = Test(5) # Test.__init__ called; sets obj.value to num (5)

print obj.getVal() # prints "5"
[/code]
The double underscores are used when operator overloading. For example, the above class could be written like this:
[code=python]
class Test:
def __init__(self, num): # called when object is constructed
self.value = num

def __repr__(self): # called when object is printed
return self.value

obj = Test(5) # Test.__init__ called; sets obj.value to num (5)

print obj # Test.__repr__ called; prints "5"
[/code]
Does that help?


Edit: Just wanted to add that the double underscores in simple terms mean that the function will get called on a special occasion (operator overloading). For example, __init__ gets called when an object is created, __repr__ gets called when the object gets printed, __del__ gets called when object goes out of scope, and there are many others.

Edit 2: Another thing, __init__ is usually used to set up the object by using the arguements to make variables of the object. For example, let's say you have a rectangle class. You'd want the object to have for instance, width and heigth variables. The __init__ would look like this:
[code=python]
class Rect:
def __init__(self, width, height):
self.width = width
self.height = height

myRect = Rect(5, 7)
[/code]

[ateale]

thanks ilikepython - it makes sense - will read over that a few more times

thanks for explaining!

[ilikepython]

thanks ilikepython - it makes sense - will read over that a few more times

thanks for explaining!

You're welcome, if you have a question, feel free to ask.