In python how do you add an attribute to a list to perform an operation?
Suppose you have a class like:
class TestClass:
def __init__(self, lst):
self.lst = lst
def test(self, lst):
"""
>>> t1 = TestClass([1,2,3,4])
>>> t1.test(self.lst).size
4
"""
if you attach the attribute size to the function test it will return the length of self.lst. So, return len(self.lst)
The issue is that:
t1.test(self.lst).size
Is equivalent to:
a = t1.test(self.lst)
a.size
You're not accessing an attribute on the method, but on the return value of the method. You may want something like this:
class TestClass:
def __init__(self, lst):
self.lst = lst
def test(self):
# do something to self.lst (rather than passing it in again)
@property
def size(self):
return len(self.lst)
>>> t = TestClass([1,2,3,4])
>>> t.test()
...
>>> t.size
4
If you really want to add this to the list, then you'll need to wrap it in something that provides the size method:
class SizeList(list):
@property
def size(self):
return len(self)
class TestClass:
def __init__(self, lst):
self.lst = SizeList(lst)
def test(self):
# do something here
return self.lst
>>> t = TestClass([1,2,3,4])
>>> t.test().size
4
return len(self.lst)- and what's that otherlstintest? What exactly are you trying to do - I suspect it isn't making function attributes...