Overloading Methods
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\
Wed Jan 21 23:29:22 EST 2009
Chris Rebert wrote:
> On Tue, Jan 20, 2009 at 10:18 AM, MRAB <google at 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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