Programming Python, Part I
Having to create an object and then set each of its members is not pleasant. It takes a lot of lines and is very error-prone—did I remember to set the tags? There's a better way to do it—using the initialization method.
This special method is called __init__, and the parameters you define it to take have to be passed in the creation of the object. A possible initialization method would be:
class Post(object): def __init__(self, title, body): self.set_title(title) self.set_body(body)
Simply add the __init__ definition to the file and reload it. We now can, and have to, set the title and body at initialization time:
>>> cool = blog.Post("Cool", "Python is cool") >>> cool.get_title() 'Cool' >>> cool.get_body() 'Python is cool' >>>
Hint: to retrieve previous lines in the REPL inside Emacs use Alt-P.
There are other special methods. Remember how ugly it was to evaluate a Post itself? Let me remind you:
>>> cool <blog.Post object at 0xb7c7e9ac>
We can solve that. There's another special method called __repr__, which is used to retrieve that string. Inside the Post class add:
def __repr__(self): return "Blog Post: %s" % self.get_title()
Reload the file, the same way you loaded it previously, and evaluate a post:
>>> ## working on region in file /usr/tmp/python... >>> cool <blog.Post object at 0xb7c7e9ac> >>>
Oops! That's not what we wanted. The problem here is that the cool object was created with an older version of the Post class, so it doesn't have the new method. That is a very common mistake, and not being prepared for it can cause a lot of headaches. But, simply re-create the object, and you are set:
>>> ## working on region in file /usr/tmp/python... >>> cool = blog.Post("Cool", "Python is cool") >>> cool Blog Post: Cool >>>
Easy—wait for the next issue of Linux Journal for Part II of this tutorial. If you really want something to do now, start learning Emacs.
José P. E. “Pupeno” Fern´ndez has been programming since...at what age is a child capable of siting in a chair and reaching a keyboard? He has experimented with more languages than can be listed on this page. His Web site is at pupeno.com, and he always can be reached, unless you are a spammer, at email@example.com.
Getting Started with DevOps - Including New Data on IT Performance from Puppet Labs 2015 State of DevOps Report
August 27, 2015
12:00 PM CDT
DevOps represents a profound change from the way most IT departments have traditionally worked: from siloed teams and high-anxiety releases to everyone collaborating on uneventful and more frequent releases of higher-quality code. It doesn't matter how large or small an organization is, or even whether it's historically slow moving or risk averse — there are ways to adopt DevOps sanely, and get measurable results in just weeks.
Free to Linux Journal readers.Register Now!
- Hacking a Safe with Bash
- Django Models and Migrations
- Secure Server Deployments in Hostile Territory, Part II
- Huge Package Overhaul for Debian and Ubuntu
- The Controversy Behind Canonical's Intellectual Property Policy
- Home Automation with Raspberry Pi
- Shashlik - a Tasty New Android Simulator
- Embed Linux in Monitoring and Control Systems
- KDE Reveals Plasma Mobile
- diff -u: What's New in Kernel Development