How to use static/helper method in a class?
I'm writting a Fraction
class and I am trying to use gcd(a,b)
in the initialization of a Fraction
object. However, when I was trying to do this it would not work WITHOUT the Fraction
part of Fraction.gcd(a,b)
. I used @staticmethod
here, but it does absolutely nothing, i.e. my code works the same without it.
Is there anyway I can call gcd
without putting Fraction.
in front of it? In Java I would normally create a static method and then just call it. I could very easily put the GCD code inside of the init, but I am trying to learn here!
I am missing a lot here. Can anyone explain: static methods, helper methods in a class and pretty much how I can use various methods inside of a class?
class Fraction(object):
def __init__(self, a, b):
if Fraction.gcd(a, b) > 1:
d = Fraction.gcd(a, b)
开发者_StackOverflow社区 self.num = a/d
self.denom = b/d
else:
self.num = a
self.denom = b
@staticmethod
def gcd(a,b):
if a > b: a,b = b,a
while True:
if b % a == 0: return a
a, b = b%a, a
def __repr__(self):
return str(self.num) + "/" + str(self.denom)
Don't forget, in Python not everything needs to be in a class. There's nothing about gcd
that makes it better-suited to being a class method than a standalone function: so take it out of the class. Now you can just call gcd(a, b)
.
Think of methods in a class just like any other class attribute -- reference them on self
:
def __init__(self, a, b):
if( self.gcd(a,b) > 1):
d = self.gcd(a,b)
It doesn't matter whether it's an instance method, class method, or static method.
While you certainly can use a staticmethod if you want to keep the code associated with the class, it's usual in Python to use a module-level function, in which case you can call it as gcd
:
def gcd(a,b):
if a > b: a,b = b,a
while True:
if b % a == 0: return a
a, b = b%a, a
class Fraction(object):
def __init__(self, a, b):
if( gcd(a,b) > 1):
d = gcd(a,b)
If you have a big method within your class that requires many calls to a static method you can define a local function object and assign the method to it so you can call this function instead.
For Static Method gdc:
class Fraction(object):
def __init__(self, a, b):
gcd = Fraction.gcd
if( gcd(a,b) > 1):
d = gcd(a,b)
self.num = a/d
self.denom = b/d
else:
self.num = a
self.denom = b
@staticmethod
def gcd(a,b):
if a > b: a,b = b,a
while True:
if b % a == 0: return a
a, b = b%a, a
def __repr__(self):
return str(self.num) + "/" + str(self.denom)
For Instance Method gdc:
class Fraction(object):
def __init__(self, a, b):
gcd = self.gcd
if( gcd(a,b) > 1):
d = gcd(a,b)
self.num = a/d
self.denom = b/d
else:
self.num = a
self.denom = b
def gcd(self,a,b):
if a > b: a,b = b,a
while True:
if b % a == 0: return a
a, b = b%a, a
def __repr__(self):
return str(self.num) + "/" + str(self.denom)
So
gcd = Fraction.gcd
and
gcd = self.gcd
will allow you to call (without Fraction at the beginning as per your request :))
gcd(a,b)
Also, if you want some basic examples of python classes and instance/static methods have a look at some of my blog posts, specially the one called "Factorial and Fibonacci in Jython":
http://carlosqt.blogspot.com/search/label/Jython
I think you are referring to Java's "import static" feature.
Just to clarify: as Java enforces object orientation, it cannot have "modules" like other languages. So using import static Math.*;
for example will make all static methods on Math
available to be called without the class name.
In Python you can just add this function outside a class and call it.
That's how static methods work. You call them via Classname.methodname()
(or via instance.methodname(), but self
won't be available inside the method).
What you want is a regular function on the module level. Define it outside the class and do not decorate it.
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