Python Note 8 (Python Utilities)

Summary
filenames = os.listdir(dir) -- list of filenames in that directory path (not including . and ..). The filenames are just the names in the directory, not their absolute paths.

import os

dir="c:/"
files=os.listdir(dir)
for path in files:
    print(path)
                 

Output :
addins
AppCompat
AppPatch
assembly
avastSS.scr
bfsvc.exe

Python Note 7 (the pickle module)

In python we can use serialization functionality using pickle module. it can save live instances of objects to files and retrieve object instances from pickled files.
Code:

import pickle

class Transaction : 
 def __init__(self,userName,trnsID,payment):
  self.userName=userName
  self.trnsID=trnsID
  self.payment=payment
 
 def __del__(self):
  print("Destructed!")
 
 def getPaymentValue(self):
  return self.payment
 
 def getUserName(self) :
  return self.userName
#end of the class

Python Note 6(Classes and Objects)

Sample Code  : General class

#define a class
class User :
 def __init__(self,name,user_id,acc_balance):
  self.Name=name
  self.User_id=user_id
  self.Acc_Balance=acc_balance
  
 def recharge(self,amount):
  self.Acc_Balance+=amount
 
 def withdraw(self,amount):
  if amount <= self.Acc_Balance :
   self.Acc_Balance-=amount
  else :
   pass #do nothing
 
 def getBalance(self): #parameter less method
  return self.Acc_Balance
  
 def __del__(self) :
  print("Destructor started!")
#end of the class
 
usr=User("Kanishka",1133,27000.00)
print("User {0} , Balance {1:5.2f}".format(usr.Name,usr.getBalance()))
usr.withdraw(2000.50) #withdrwaw money
print("User {0} , Balance {1:5.2f}".format(usr.Name,usr.getBalance()))

Python Note 5 (File Handling)

File handling is very easy in python, Lets see an example

datafile=open("myfile.dat","w") #open a file for writing
datafile.write("Sri Lanka,India,Pakistan,Bhutan,Australlia,Canada") #write data
datafile.write("\n")
datafile.write("Apple,Orange,Mango")
datafile.close() #release the file

#reading from the file
datafile=open("myfile.dat","r") #open file for reading
record=datafile.readline()#reding a line (here it is the first line)
mylist=record.strip("\n").split(",") #remove newline character and split the string by comma
print(mylist)
print(len(mylist))

Python Note 4( String Formatting)

Code

import math 

for x in range(1,20) :
 print ("{0:2d} {1:3d} {2:5d}".format(x,x*2,x*3))
 
tmplate="My {} is {}"
print(tmplate.format("country","Sri Lanka"))
print(tmplate.format("name","Kanishka"))

tmplate="Hello {name} , your role is {role}"
print(tmplate.format(name="Kanishka",role="Admin"))
print(tmplate.format(name="Sampath",role="User"))

print("The value of 'PI' is approximately {0:0.3f}".format(math.pi))
print("The value of 'e' is approximately {0:0.5f}".format(math.e))

#old formatting
print('The value of PI is approximately %5.3f' % math.pi)

Result

Python Note 3 (Functions)

We can define number of functions in same python script.
Code

#function1
def cube(x) :
 return x**3

#function2
def maxVal(x,y) :
 if x > y :
  return x
 else :
  return y

print (cube(3))
print (maxVal(12,22))

Python Note 2 (String manipulations)

Code

mystr="Sri Lanka"
print( len(mystr) )
print( mystr.upper() )
print( mystr.lower() )
print( mystr[1])
print( mystr[-1])

Python Note 1

Python is an interpreted language. Nesting is done using indentation. I have used Python 3.2.2 in this note.

Sample python program demonstrating Python operators.