Chris Rebert wrote:
On Tue, Jan 20, 2009 at 10:18 AM, MRAB <goo...@mrabarnett.plus.com> wrote:
K-Dawg wrote:
Can you overload methods in Python?
Can I have multiple __inits__ with different parameters passed in?
Simple answer: no.
More complicated answer: Yes, with some caveats.
You usually don't need to overload methods in Python since you can use
default and keyword arguments instead. For instance:
class Foo(object):
def __init__(self, a, b=10, c=None):
self.a = a
self.b = b
if c is None: c = []
self.c = c
#example use
x = Foo("#", 4, [6,7])
y = Foo("@")
z = Foo("!", c=[1,2])
Whereas in Java or C++ this would require several overloads, it can be
succinctly expressed as a single method in Python.
However, if you want the overloads to accept completely different
types as parameters, then it arguably should expressed as distinct
methods rather than "overloads". In the special case of __init__, you
might want to make the alternate initializers classmethods or factory
functions.
Cheers,
Chris
To elaborate on what Chris said, I usually find myself using class
factory functions. Suppose you have a class that you want to initialize
from a string, a file pointer, or a path. Here's how I'd implement it:
class MyClass:
def __init__(self, bytes):
<whatever init code>
@classmethod
def FromFilePointer(self, fp):
bytes = fp.read()
return MyCass.FromBytes(bytes)
@classmethod
def FromPath(self, path):
bytes = open(path, "r").read()
return MyCass.FromBytes(bytes)
@classmethod #Yes, I know this duplicates __init__,
def FromBytes(self, bytes): #but I include it so as to provide
return MyClass(bytes) #3 parallel methods for initializing.
myclass = MyClass.FromFilePointer(open("myfile.txt", "r"))
myclass = MyClass.FromPath("myfile.txt")
myclass = MyClass.FromBytes("spam-spam-spam")
That might be a little bit more work, but I think it reads better and is
more flexible down the road.
-greg
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