Reputation: 20856

Python classes clarification

I saw this below piece of code in a book and would like to know how it works..I tried to understand myself but get stuck in few places..I know its more like a teaching question but hopefully in the forum will help me..

Code:

import os
import re

class Wiki:
    "A class representing a wiki as a whole."
    HOME_PAGE_NAME = "HomePage"
    def __init__(self, base):
        "Initializes a wiki that uses the provided base directory."
        self.base = base
        if not os.path.exists(self.base):
            os.makedirs(self.base)
        elif not os.path.isdir(self.base):
            raise IOError('Wiki base "%s" is not a directory!' % self.base)
    def getPage(self, name=None):
        """Retrieves the given page for this wiki, which may or may not
        currently exist."""
        if not name:
            name = self.HOME_PAGE_NAME
        return Page(self, name)

class Page:
    """A class representing one page of a wiki, containing all the
    logic necessary to manipulate that page and to determine which other
    pages it references."""
    #We consider a WikiWord any word beginning with a capital letter,
    #containing at least one other capital letter, and containing only
    #alphanumerics.
    WIKI_WORD_MATCH = "(([A-Z][a-z0-9]*){2,})"        
    WIKI_WORD = re.compile(WIKI_WORD_MATCH)
    WIKI_WORD_ALONE = re.compile('^%s$' % WIKI_WORD_MATCH)
    def __init__(self, wiki, name):
        """Initializes the page for the given wiki with the given
        name, making sure the name is valid. The page may or may not
        actually exist right now in the wiki."""
        #WIKI_WORD matches a WikiWord anywhere in the string. We want to make
        #sure the page is a WikiWord and nothing else.
        if not self.WIKI_WORD_ALONE.match(name):
            raise(NotWikiWord, name)
        self.wiki = wiki
        self.name = name
        self.path = os.path.join(self.wiki.base, name)
    def exists(self):
        "Returns true if there's a page for the wiki with this name."
        return os.path.isfile(self.path)
    def load(self):
        "Loads this page from disk, if it exists."
        if not hasattr(self, 'text'):
            self.text = ''
            if self.exists():
                self.text = open(self.path, 'r').read()    
    def save(self):
        "Saves this page. If it didn't exist before, it does now."
        if not hasattr(self, 'text'):
            self.text = ''
        out = open(self.path, 'w')
        out.write(self.text)
        out.close()
    def delete(self):
        "Deletes this page, assuming it currently exists."
        if self.exists():
            os.remove(self.path)
    def getText(self):
        "Returns the raw text of this page."
        self.load()
        return self.text

class NotWikiWord(Exception):
    """Exception thrown when someone tries to pass off a non-WikiWord
     as a WikiWord."""
    pass

In Python shell:

 >  >  >  from BittyWiki import Wiki
 >  >  >  wiki = Wiki(“localwiki”)
 >  >  >  homePage = wiki.getPage()
 >  >  >  homePage.text = “Here ’ s the home page.\n\nIt links to PageTwo and 
PageThree.”
 >  >  >  homePage.save()

This is my understanding.

2 classes are created a) Wiki and b)Page
Page classes stores all the information related to a page.

Questions:

We create a method object -homepage but how does the homepage.save() works..homepage is a object of Wiki and save() is a method of page object. how come it works?

Any clarification would be really helpful

Upvotes: 0