confused if i should be doing type checking in the code ( a confused java programmer)

[Jeffrey Drake]

There are a few solutions:

1.
	class Hi:
		__donttouchmeImPrivate = 4

2.	Python 2.2+ look for 'properties'

3.	use __getstate__ and __setstate__ (look them up in 'special
functions' in the manual

4. 	goto #python on irc.openprojects.net and ask dash, and he will
say you don't need constants in python (more info: talk to him)

Regards,
Jeffrey Drake
	

On Sun, 6 Jan 2002 12:54:38 +0530, Karthik Gurumurthy
<karthikg at aztec.soft.net> wrote:

>hi all,
>
>have been doing python for a couple of months now and have been doing java
>for more than a year now.
>
>had trouble implementing immutable constants in python
>
>i wanted a public static "final" equivalent in python.
>
>class MovieRating:
>	REGULAR = 1
>	NEW = 2
>	CHILDREN = 3
>
>Now even though i can access it like
>
>MovieRating.REGULAR
>But someone can modify the value
>
>MovieRating.REGULAR = 100 # UnAcceptable
>
>I was trying to emulate the java enum equivalent but was not able
>implement it successfully.
>
>class MovieRating{
>
> public static final MovieRating REGULAR = new MovieRating(1)
> public static final MovieRating NEW = new MovieRating(2)
> public static final MovieRating CHILDREN = new MovieRating(3)
>
> private int value;
>
> private MovieRating(int i){
>  value = i;
> }
>}
>
>Now the client cannot instantiate MovieRating but can get all the constant
>instances.
>so there's a proper type checking in another code which accepts only
>MovieRating instances
>instead of just integers.
>
>So in python code i needed a singleton and then the immutable constants.
>Then came across this recipie in Cookbook and Well it's brillaint!
>i had'nt even imagined such things could be done.
>
>http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/65207
>
>I used that code and wrote this:
>
>class _MovieRating:
>	def __init__(self):
>		self.__dict__['REGULAR'] = 1
>		self.__dict__['NEW'] = 2
>		self.__dict__['CHILDREN'] = 3
>	def __setattr__(self,name,value):
>		if self.__dict__.has_key(name):
>			raise "Cannot assign to a readonly movie rating %s" % (name,)
>		else:
>			raise "Cannot add new constants"
>
>import sys
>sys.modules[__name__] = _Movie()
>
>So in java if there's a functon which accepts the movie ratings,
>
>void func(MovieRating rating,<something else){
>
>}
>
>We have been taught to use enum pattern in java to store constants instead
>of primtives like
>ints or strings because we get the benefit of type checking in the compile
>stage itself and no one
>can send in a wrong rating value.
>
>Since this kind of a things cannot be done in python ,should i be writing
>this kind of code in python as well??
>
>def func(rating,x)
>	if type(rating) != MovieRating:
>		raise 'You have passed an Incorrect type'
>
>if i do that then all my python functions and methods will be littered with
>such type checking code!
>
>even after a couple of months of python..i think i have not been able to
>understand the differences in the way
>you code in java and python!  :-(
>probably am missing something here..the purpose of the 2 languages appear to
>be very different to me now.
>
>anyways,
>i took a look at the __slots__ concept as well which i guess does not allow
>us to add attributes to an instance.
>I saw a recipe for writing properties. That was smart!
>But now python supports properties at syntax level. I tried that out with
>py2.2
>
>Then what prevents python from having a final equivalent when we could have
>such nice things like properties?
>
>thanks for your patience!
>karthik.
>
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>
>-----Original Message-----
>From: tutor-admin at python.org [mailto:tutor-admin at python.org]On Behalf Of
>Kirk D Bailey
>Sent: Sunday, January 06, 2002 10:42 AM
>To: tutor at python.org
>Subject: [Tutor] TLlistmaster.py
>
>
>To whoever feels like it;
>I have got TLlistmaster.py almost complete. There is one minor bug in
>there. Regretfully, it's a tiny little stinkbug and it is driving me
>crazy(ier).
>
>First, take a look at the script as it stands this very instant- page
>inherently self updates.
>
>http://www.howlermonkey.net/TLlistmaster.shtml
>
>Second, there is no error code, but it fails to see the presence of
>the subject line in the pending file.
>
>Here is the screen capture from a sample run:
>(beware wordwrap)
>ns# ./TLlistmaster.py < testfile
>From:= highprimate at howlermonkey.net
>Subject field as extracted:='Re: join highprimate at howlermonkey.net
>evil-humor 1010287984'
>CLEANED UP subject line='join highprimate at howlermonkey.net evil-humor
>1010287984'
>command='join'
>oldfrom='highprimate at howlermonkey.net'
>listname='evil-humor'
>Pending action='join testcode at howlermonkey.net testlist3 1010173860'
>This person wants to join'evil-humor' list!
>cannot find subject in pending file!
>ns#
>
>I included a LOT of print statements in the program to generate all
>these status reports. The language's interpeter is not creating ANY
>errors.
>
>I am stumped for the moment, and tired, and battling with a cranky
>isp, so I think I will smoke a house pipe and drink some fine coniac
>and go night night, but feel free to look at this, and write me some
>questions, answers, suggestions, pithy things to double check, evil
>jokes, etc...
>
>So close... SO close...
>
>
>
>
>
>
>
>
>
>
>
>
>end
>
>In total confusion,
>                   Kirk D Bailey
>
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