Strange Coincidence
Great Stuff
Python not only offers generators with the yield
keyword; classes can also implement generators as iterators. For this the Pythonista defines two methods: __iter__()
and __next__()
. The quadruple underscores ("dunders") mark the official entry points for Python's standard library. If the Python interpreter sees a loop head like for n in Roulette()
, it instantiates an object of the Roulette
class, uses __iter__()
to access its iterator, and then retrieves new values from it with calls to __next__()
until the iterator throws an exception.
In the class defined in Listing 2, __iter__()
conveniently returns the Roulette
instance itself, because the class does not need a separate iterator, since it implements the iterator itself with __next__()
. The latter always returns a new random number in the range 0 to 36 and never throws an exception, so that the flow of the for
loop in the main program never stops.
Listing 2
roulette.py
01 #!/usr/bin/env python3 02 import random 03 04 class Roulette: 05 slots = 36 06 numbers = range(0,slots+1) 07 08 def __iter__(self): 09 return self 10 11 def __next__(self): 12 return self.__class__.numbers[random.randint(0, self.__class__.slots)]
The Roulette
class defines two class variables: slots
as the highest number on the roulette
wheel and numbers
as a sequence of numbers from 0 to 36 inclusive. It makes sense to define the variables once only for the class and not to rebuild them for each instance or even every time the iterator is called.
Class or Instance?
Python's class variables differ from instance variables in that they are not accessed with self.variable
, but with __class__.variable
or self.__class__.variable
. For read-only access, you could even reference the class variable using the self.variable
instance path.
But if you modify the latter, you may be in for a surprise, because Python creates a new instance variable behind your back. The instance variable will be decoupled from the class variable so that each object will modify its own, instead of propagating changes to the class level. Also, methods do not find the class variable simply by its name; if you simply reference slots
in __iter__()
, you can expect the syntax checker to blow up in your face.
As so often in the Python world, there is a small but subtle difference between versions 2 and 3: The iterator entry into the generator class goes by the name of next
in Python 2 and not __next__
as in Python 3; programmers who want to use both versions thus typically simply define another next()
method, which passes the parameters fed to it to __next__()
without modification. Python 3 does not use next()
, so the compatibility trick does no harm there.
The output of the statistical evaluation of the roulette generator is shown in Listing 3. After 27 rounds, a doublet appeared for the first time: the number 11 occurred twice in a row. After 6,249 rounds of Faites vos jeux, 15 occurred three times in a row; after 57,393 games, 34 occurred four times in a row, and so on.
Listing 3
roulette-run
1 $ ./roulette 2 max_run: 2 11 (27) 3 max_run: 3 15 (6249) 4 max_run: 4 34 (57393) 5 max_run: 5 1 (3363284) 6 max_run: 6 0 (95846456) 7 max_run: 7 26 (357289507)
Tumultuous Scenes
What would happen in Las Vegas at a roulette table if zero came up come six times in a row as in Listing 3 after 95 million rounds? Tumultuous scenes would probably take place in the casino before the pit boss appeared and sent the croupier home for the day, because every player at the table would immediately suspect that something fishy was going on. But, seen statistically, everything is above board; it's an inevitable fact that even random values will repeat at some time.
« Previous 1 2 3 Next »
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
Fedora 41 Beta Available with Some Interesting Additions
If you're a Fedora fan, you'll be excited to hear the beta version of the latest release is now available for testing and includes plenty of updates.
-
AlmaLinux Unveils New Hardware Certification Process
The AlmaLinux Hardware Certification Program run by the Certification Special Interest Group (SIG) aims to ensure seamless compatibility between AlmaLinux and a wide range of hardware configurations.
-
Wind River Introduces eLxr Pro Linux Solution
eLxr Pro offers an end-to-end Linux solution backed by expert commercial support.
-
Juno Tab 3 Launches with Ubuntu 24.04
Anyone looking for a full-blown Linux tablet need look no further. Juno has released the Tab 3.
-
New KDE Slimbook Plasma Available for Preorder
Powered by an AMD Ryzen CPU, the latest KDE Slimbook laptop is powerful enough for local AI tasks.
-
Rhino Linux Announces Latest "Quick Update"
If you prefer your Linux distribution to be of the rolling type, Rhino Linux delivers a beautiful and reliable experience.
-
Plasma Desktop Will Soon Ask for Donations
The next iteration of Plasma has reached the soft feature freeze for the 6.2 version and includes a feature that could be divisive.
-
Linux Market Share Hits New High
For the first time, the Linux market share has reached a new high for desktops, and the trend looks like it will continue.
-
LibreOffice 24.8 Delivers New Features
LibreOffice is often considered the de facto standard office suite for the Linux operating system.
-
Deepin 23 Offers Wayland Support and New AI Tool
Deepin has been considered one of the most beautiful desktop operating systems for a long time and the arrival of version 23 has bolstered that reputation.