I'd like advice/opinions on when it is appropriate to do
attribute/property validation in python. I'm coming from a C#/Java
background, where of course tons of "wasted" code is devoted to
property validation. Here is a toy example illustrating my question:
# Example: mixing instance attributes with properties. Is it pythonic to
# validate property data in setters? Since tens and ones are never
# validated, the class can be "broken" by setting these directly
class SillyDecimal(object):
"""A silly class to represent an integer from 0 - 99."""
def __init__(self, arg=17):
if isinstance(arg, tuple):
self.tens = arg[0]
self.ones = arg[1]
else:
self.number = arg
def getNumber(self):
return self.tens*10 + self.ones
def setNumber(self, value):
if value < 0 or value > 99:
raise ArgumentException("Must in [0, 99]")
self.tens = value // 10
self.ones = value % 10
number = property(getNumber, setNumber, None, "Complete number, [0-99]")
x = SillyDecimal()
x.number, x.tens, x.ones # returns (17, 7, 1)
Even though "tens", "ones" and "number" all appear as attributes, only
"number" has its input validated. Since the class is designed to only
hold numbers 0 - 99, one can 'break' it by setting self.tens=11, for
example. Should tens and ones be made into full-fledged properties
and validated? Should number have no validation? Is it more pythonic
to encapsulate tightly, or rely on "responsible use."
Marcus 2 1419
I don't use properties that much, but when I use them
I put them *outside* the class, in a property factory.
Here is an example I have prepared for my course at
PyUK, using a property to crypt a password attribute:
class User(object):
def __init__(self, username, password):
self.username, self.password = username, password
def cryptedAttribute(seed="x"):
def get(self):
return getattr(self, "_pw", None)
def set(self, value):
self._pw = crypt(value, seed)
return property(get, set)
User.pw = cryptedAttribute()
I feel that:
1) separation of concerns is of the utmost importance;
2) classes should be kept as short as possible.
Notice that in this design getters and setters are
really hidden from the user, which may be or may be
not what you want.
Michele Simionato
> Even though "tens", "ones" and "number" all appear as attributes, only "number" has its input validated. Since the class is designed to only hold numbers 0 - 99, one can 'break' it by setting self.tens=11, for example. Should tens and ones be made into full-fledged properties and validated? Should number have no validation? Is it more pythonic to encapsulate tightly, or rely on "responsible use."
You could make them double-underscored attributes. That creates some
name-mangling that prevents accidential access. But as there is no real
private concept in python (and java and C++ protection can be easily
overcome), it is considered pythonic to rely on responsible use. If a
design for abuse-protection is the ultimate goal, the common suggestion is
to use IPC mechanisms to prevent in-process sharing of data and code -
that's the only real way to go, regardless of the used language.
--
Regards,
Diez B. Roggisch This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics
by: Tom Evans |
last post by:
My basic question:
If I have a specific interface which I know is going to be implemented
by a number of classes, but there is no implementation commonality
between them, what is the preferred...
|
by: asdf sdf |
last post by:
i need some advice. i'm a back end programmer historically, but have
been exploring python for webapps and enjoying it.
i need to build some simple Win client-server or standalone apps.
the...
|
by: Nickolay Kolev |
last post by:
Hi all,
I would like to find a more pythonic way of solving the following:
Having a string consisting of letters only, find out the total sound
score of the string. The sound score is...
|
by: Charles Krug |
last post by:
I've a function that needs to maintain an ordered sequence between
calls.
In C or C++, I'd declare the pointer (or collection object) static at
the function scope.
What's the Pythonic way to...
|
by: Carl J. Van Arsdall |
last post by:
It seems the more I come to learn about Python as a langauge and the way
its used I've come across several discussions where people discuss how
to do things using an OO model and then how to design...
|
by: jnair |
last post by:
My Tead Lead my object counter code seen below is not pythonic
class E(object):
_count = 0
def __init__(self):
E._count += 1
count = property(lambda self: E._count )
def test():
if...
|
by: jnair |
last post by:
My Team Lead says my object counter code seen below is not pythonic
class E(object):
_count = 0
def __init__(self):
E._count += 1
count = property(lambda self: E._count )
def test():...
|
by: Frank Samuelson |
last post by:
I love Python, and it is one of my 2 favorite
languages. I would suggest that Python steal some
aspects of the S language.
-------------------------------------------------------
1. Currently...
|
by: Hussein B |
last post by:
Hey,
Well, as you all know by now, I'm learning Python :)
One thing that is annoying my is the OOP in Python.
Consider this code in Java:
--
public class Car {
private int speed;
private...
|
by: taylorcarr |
last post by:
A Canon printer is a smart device known for being advanced, efficient, and reliable. It is designed for home, office, and hybrid workspace use and can also be used for a variety of purposes. However,...
|
by: aa123db |
last post by:
Variable and constants
Use var or let for variables and const fror constants.
Var foo ='bar';
Let foo ='bar';const baz ='bar';
Functions
function $name$ ($parameters$) {
}
...
|
by: ryjfgjl |
last post by:
If we have dozens or hundreds of excel to import into the database, if we use the excel import function provided by database editors such as navicat, it will be extremely tedious and time-consuming...
|
by: BarryA |
last post by:
What are the essential steps and strategies outlined in the Data Structures and Algorithms (DSA) roadmap for aspiring data scientists? How can individuals effectively utilize this roadmap to progress...
|
by: nemocccc |
last post by:
hello, everyone, I want to develop a software for my android phone for daily needs, any suggestions?
|
by: Hystou |
last post by:
There are some requirements for setting up RAID:
1. The motherboard and BIOS support RAID configuration.
2. The motherboard has 2 or more available SATA protocol SSD/HDD slots (including MSATA, M.2...
|
by: Hystou |
last post by:
Most computers default to English, but sometimes we require a different language, especially when relocating. Forgot to request a specific language before your computer shipped? No problem! You can...
|
by: Oralloy |
last post by:
Hello folks,
I am unable to find appropriate documentation on the type promotion of bit-fields when using the generalised comparison operator "<=>".
The problem is that using the GNU compilers,...
|
by: jinu1996 |
last post by:
In today's digital age, having a compelling online presence is paramount for businesses aiming to thrive in a competitive landscape. At the heart of this digital strategy lies an intricately woven...
| |