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| For 2023 (and 2024 ...) - we are now fully retired from IT training. We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk. Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active! I am also active in many other area and still look after a lot of web sites - you can find an index ((here)) |
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Inheritance
In (Object Oriented) programming terms, "Inheritance" is used to define a type of data (an "object") which behaves like another type of data with some additions and differences. For example, we can define a type of data that's a piece of clothing. We can then define a pair of shoes which is like a piece of clothing, except that it has two extra pieces of information involved - a length and a width. Languages that are known as Object Oriented languages provide facilities to make such definitions easy without repeating code. In the following piece of code (in Python), we define a piece of clothing (it's known as a base class) and then we extend it into a new class (called a subclass) which has the same code and properties as a piece of clothing, with the exception of changes that we list. The tshirt and tights classes are also subclasses of clothing and we can make up a list of pieces of clothing (you'll see it done in the test code at the bottom) which we can then loop through reporting colour and size. As we loop through in this way, the getcolour method is INHERITED from the clothes base class in each case (i.e. it is common code) and the getsize method uses what we call POLYMORPHISM as it uses different code to return the size for different types of clothing. class clothing: def __init__(self,colour,weight): self.colour=colour self.weight=weight def getcolour(self): return self.colour def getsize(self): return "n/a" class shoes(clothing): def __init__(self,colour,weight,len,wid): clothing.__init__(self,colour,weight) self.length = len self.width = wid def getsize(self): r = "Length "+str(self.length)+" and width "+self.width return r class tshirt(clothing): def __init__(self,colour,weight,size): clothing.__init__(self,colour,weight) self.size = size def getsize(self): return self.size class tights(clothing): pass if __name__ == "__main__": wearing = [] wearing.append(tshirt("blue",1.0,"XL")) wearing.append(tights("pink",0.1)) wearing.append(shoes("brown",2.0,11,"D")) for haveon in wearing: print "I am wearing something",haveon.getcolour(), print " size ",haveon.getsize() Let's run that ... [localhost:~/ipy] graham% python dresser I am wearing something blue size XL I am wearing something pink size n/a I am wearing something brown size Length 11 and width D [localhost:~/ipy] graham% See also further examples and Python object training Please note that articles in this section of our
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