Month: May 2011

Classes

Since Python is a object oriented programming language then you can use things like classes to define a object, a class is a bunch of methods that act on the data that is stored within the class itself. You can store data within the class, but unlike c++/java/c# etc, there is no private/public/protected, everything is public accessible.

In the example below, the class constructor is called (__init__ method) and the first parameter is the class object itself, which is why it is there and for many reasons why it is called self as a variable name.

 
#  self means the object itself.
 
class mysimpleclass :
        __myvar = 0
        def __init__(self,value = 0) :
                self.__myvar = value
 
        def printValue(self) :
                print self.__myvar
 
simple = mysimpleclass(5)
simple.printValue()

the printValue method just does that, it will print the value that is sorted within the class object and here is the output

5

if you did not put in the self in the example above for printing out the class object variable __myvar as below

class mysimpleclass ....
       ....
       def printValue() :
            print __myvar

the error would be

NameError: global name '_mysimpleclass__myvar' is not defined

because the interrupter is looking for a global variable and not a variable attached to that object.

Add two numbers

To carry on my normal process of notes on this website for different languages here is the how to add two numbers with a return value from a function.

To define a function you use the “def” syntax within the programming language and then the next bit of text before the parameters for the function itself ( in this case the parameters are the (number1, number2) ), is the function name and how to call the function.

The function below takes two parameters and returns back there result of the mathematical addition, the last part is how to call the function.

def addTwo(number1, number2) : 
	return number1 + number2
 
print addTwo(1,2)

and the output would be

3

Read / Write

Here is how to open and read/write to a file within Python. Most languages supply a basic file opening and read/writing methods with the closing method, and Python is no different which makes going from one language to another very easy (you just need to learn the classes that are capable to doing the interesting stuff 🙂 ).

To write to a file, you have to open it first within a write mode (‘w’) and then write to that file *handler*, in the code below the variable ‘f’ is the file *handler*

f = open('write.txt','w');
f.write('hi there\n');
f.write('this is genux\n');
f.write('and my site is codingfriends.com\n');
f.write('pyhon does OO\n');
f.close();
print 'File has been written\n';

which will write to the “write.txt” the following text

hi there
this is genux
and my site is codingfriends.com
pyhon does OO

and then to read in the file you use the read mode ‘r’, you are able to use the Iterator style of coding with using a ‘for in :’ or if you wish to read one line at a time you can use the ‘readline()’ method, and to seek within a file you use the method ‘seek()’.

f = open('write.txt','r');
for readInLine in f:
	print readInLine;
 
print 'seek to the start of the file';
f.seek(0);
anotherLine = f.readline();
print anotherLine;
 
f.close();

and here is the output

hi there
 
this is genux
 
and my site is codingfriends.com
 
pyhon does OO
 
seek to the start of the file
hi there