Introduction to Python

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Contents

How to install Python on Linux
How to run a Python program
The basic of Python codes
Data expressions
Built-in functions in Python
Interactive input/output
Conditional statement for Python
Loop structure for Python
Creating your own functions
Python modules
Reading/writing files for Python
Error handling code
Object Oriented Programming (OOP)
Tkinter package for GNU programming

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Reading/writing files for Python

The open() command can read or write out an external file. The second argument of open() specifies read (r) or write (w) a file. The following example is reading a file:

file0 = open("python.txt","r") for line in file0.readlines():    print line file0.close()

This example code copies a file and outputs it in a different name.

inf = open("python.txt","r") outf = open("python.py","w") while line:    outf.write(line)    line = inf.readline() print "python.txt has been copied into python.py." inf.close() outf.close()

The following is an application of the above. You can modify the content of an existent file by a code:

import os,time test = open("test.py","r") outf1 = open("test.tmp","w") header = "Test for %s " %time.ctime(time.time()) # Add a line outf1.write(header+"\n\n") lines = test.readlines() for i in range(2,len(lines)):    outf1.write(lines[i]) outf1.close test.close() # Changing the file names. os.rename("test.py","test.bak") os.rename("test.tmp","test.txt") os.remove("test.bak")

This is a typical example to make an output file of your calculation.

#!/usr/bin/python from numpy import * from math import * outf = open("out.d","w") x=0.0 for i in range(1,1000,1):    y=math.log1p(x) #math.log1p is the natural log.    outf.write(str(x)+" "))    outf.write(str(y)+"\n")    x+=0.1 outf.close()

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