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Python Programming - 1


Introduction
  • Python was designed to be easy to understand and fun to use
  • Name came from Monty Python to indicate fun to use
  • You can build prototypes and tools quickly with Python
  • Python is Interpreted



Environment Setup
  • Download reference https://python.org/download
  • Select a version such as 2.7
  • Install and set up PATH environment variable with “installed directory path>” (c:/python27)
  • Use Python GUI – IDLE as editor


Basic Syntax 
  • no types for variables
  • pthon indentation
          if True:
            print "True"
         else:
           print "False"
    
  • Comments
           Use # to comment
  • Coding in .py file
           python test.py
  • Passing argurmts
            $ python test.py arg1 arg2 arg3
            ——————–
            import sys
            print 'Number of arguments:', len(sys.argv), 'arguments.'
            print 'Argument List:', str(sys.argv)
            ————————



Variable and Data Types 
  • Numbers
        int, long, float
    
  • Strings
          Built-in string class named "str" with many handy features
          ------------------------------    
          str = 'Hello World!'
          print str # Prints complete string
          print str[0] # Prints first character of the string
          print str[2:5] # Prints characters starting from 3rd to 5th
          print str[2:] # Prints string starting from 3rd character
          print str * 2 # Prints string two times
          print str + "TEST" # Prints concatenated string
          print str[-1] # Prints !
          print str[:-3]
          -----------------------------------



  • Lists
           list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
           tinylist = [123, 'john']
           print list # Prints complete list
           print list[0] # Prints first element of the list
           print list[1:3] # Prints elements starting from 2nd till 3rd
           print list[2:] # Prints elements starting from 3rd element
           print tinylist * 2 # Prints list two times
           print list + tinylist # Prints concatenated lists
    



 
  • Python Tuples
           Tuples can be thought of as readonly lists
    
            tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
            tinytuple = (123, 'john')
            print tuple # Prints complete list
            print tuple[0] # Prints first element of the list
            print tuple[1:3] # Prints elements starting from 2nd till 3rd
            print tuple[2:] # Prints elements starting from 3rd element
            print tinytuple * 2 # Prints list two times
            print tuple + tinytuple # Prints concatenated lists
    
           tuple = ( 'abcd', 786 , 2.23, 'john', 70.2 )
           tuple[2] = 1000 # Invalid syntax with tuple
           list = [ 'abcd', 786 , 2.23, 'john', 70.2 ]
           list[2] = 1000 # Valid syntax with list
  • Python dictionary    
           Python's dictionaries are kind of hash table type


 
  • Operator
 
  • Arithmetic Operators
  • Comparison (Relational) Operators
  • Assignment Operators
  • Logical Operators
  • Bitwise Operators
  • Membership Operators
  • Identity Operators
  • Arithmetic Operators     
        ----------------------------------
        a = 21
        b = 10
        c = 0
        c = a + b
        print "Line 1 - Value of c is ", c
        c = a - b
        print "Line 2 - Value of c is ", c
        c = a * b
        print "Line 3 - Value of c is ", c
        c = a / b
        print "Line 4 - Value of c is ", c
        c = a % b
        print "Line 5 - Value of c is ", c
        a = 2
        b = 3
        c = a**b
        print "Line 6 - Value of c is ", c
        a = 9.0
        b = 2.0
        c = a/b
        print "Line 7 - Value of c is ", c
        ----------------------------------------------


  • Comparison Operator

        ———————————————–

        a = 21
        b = 10
        c = 0
        if ( a == b ):
         print "Line 1 - a is equal to b"
        else:
         print "Line 1 - a is not equal to b"
        if ( a != b ):
         print "Line 2 - a is not equal to b"
        else:
         print "Line 2 - a is equal to b"
        if ( a <> b ):
         print "Line 3 - a is not equal to b"
        else:
         print "Line 3 - a is equal to b"
        if ( a < b ):
          print "Line 4 - a is less than b"
        else:
          print "Line 4 - a is not less than b"
        if ( a > b ):
         print "Line 5 - a is greater than b"
        else:
         print "Line 5 - a is not greater than b"
         a = 5;
         b = 20;
        if ( a <= b ):
         print "Line 6 - a is either less than or equal to b"
        else:
         print "Line 6 - a is neither less than nor equal to b"
        if ( b >= a ):
         print "Line 7 - b is either greater than or equal to b"
        else:
         print "Line 7 - b is neither greater than nor equal to b"
 
         ————————————————-

 
  • Assignment Operator
         ---------------------------------------------------
          a = 21
          b = 10
          c = 0
          c = a + b
          print "Line 1 - Value of c is ", c
          c += a
          print "Line 2 - Value of c is ", c
          c *= a
          print "Line 3 - Value of c is ", c
          c /= a
          print "Line 4 - Value of c is ", c
          c = 2
          c %= a
          print "Line 5 - Value of c is ", c
          c **= a
          print "Line 6 - Value of c is ", c
          c //= a
          print "Line 7 - Value of c is ", c
          ------------------------------------------------------

  • Bitwise Operator
         —————–
         a = 0011 1100
         b = 0000 1101
         a&b = 0000 1100
         a|b = 0011 1101
         a^b = 0011 0001
         ~a = 1100 0011
         << Binary Left Shift
         >> Binary Right Shift
         ——————————-

 
  • Logical Operators
         --------------------------------
          and
          or
          not
         -------------------------------

        Membership Operators
        --------------------------------
        a = 10
        b = 20
        list = [1, 2, 3, 4, 5 ];
        if ( a in list ):
         print "Line 1 - a is available in the given list"
        else:
         print "Line 1 - a is not available in the given list"
        if ( b not in list ):
         print "Line 2 - b is not available in the given list"
        else:
         print "Line 2 - b is available in the given list"
         a = 2
        if ( a in list ):
         print "Line 3 - a is available in the given list"
        else:
         print "Line 3 - a is not available in the given list"
        ------------------------------------
ez

  • Identity Operators
        —————————————
 
        a = 20
        b = 20
        if ( a is b ):
         print "Line 1 - a and b have same identity"
        else:
         print "Line 1 - a and b do not have same identity"
        if ( id(a) == id(b) ):
         print "Line 2 - a and b have same identity"
        else:
         print "Line 2 - a and b do not have same identity"
         b = 30
        if ( a is b ):
         print "Line 3 - a and b have same identity"
        else:
         print "Line 3 - a and b do not have same identity"
        if ( a is not b ):
         print "Line 4 - a and b do not have same identity"
        else:
         print "Line 4 - a and b have same identity"

         —————————————————-


 
  • Conditional Statements
           if statements
           if else
           nested if

           var = 100
           if var == 200:
            print "1 - Got a true expression value"
            print var
           elif var == 150:
            print "2 - Got a true expression value"
            print var
           elif var == 100:
            print "3 - Got a true expression value"
            print var
           else:
            print "4 - Got a false expression value"
            print var
            print "Good bye!"



  • Loops
            while
            while .. else

           count = 0
           while count < 5:
            print count, " is less than 5"
            count = count + 1
          else:
           print count, " is not less than 5"
 
         
           For

           for letter in 'Python': # First Example
            print 'Current Letter :', letter
            fruits = ['banana', 'apple', 'mango']
           for fruit in fruits: # Second Example
            print 'Current fruit :', fruit
            print "Good bye!"
            fruits = ['banana', 'apple', 'mango']
           for index in range(len(fruits)):
            print 'Current fruit :', fruits[index]
            print "Good bye!"




           Nesting of loops
           
            i = 2
            while(i < 100):
            j = 2
            while(j <= (i/j)):
            if not(i%j): break
            j = j + 1
            if (j > i/j) : print i, " is prime"
            i = i + 1
            print "Good bye!"


           Loop Control Statements
           break
           continue
           pass



  • Functions
         ———————————————-
           # Function definition is here
           def printme( str ):
           "This prints a passed string into this function"
            print str;
            return;
            # Now you can call printme function
            printme("I'm first call to user defined function!");
            printme("Again second call to the same function");
            ————————————————–
     
             Pass by reference
            ———————————–
            # Function definition is here
            def changeme( mylist ):
            "This changes a passed list into this function"
             mylist.append([1,2,3,4]);
             print "Values inside the function: ", mylist
             return
             # Now you can call changeme function
              mylist = [10,20,30];
              changeme( mylist );          
              print "Values outside the function: ", mylist
              —————————————–

              Function Arguments
              You can call a function by using the following types of formal arguments:
  •     Required arguments
  •     Keyword arguments
  •     Default arguments
  •     Variable-length arguments

             ————————————
             # Function definition is here
             def printinfo( name, age = 35 ):
             "This prints a passed info into this function"
             print "Name: ", name;
             print "Age ", age;
             return;
             # Now you can call printinfo function
             printinfo( age=50, name="miki" );
             printinfo( name="miki" );
             ——————————————————

             Variable-length arguments

             ——————————————————

             # Function definition is here
             def printinfo( arg1, *vartuple ):
             "This prints a variable passed arguments"
              print "Output is: "
              print arg1
              for var in vartuple:
              print var
              return;
              # Now you can call printinfo function
              printinfo( 10 );
              printinfo( 70, 60, 50 );

              ————————————————


ittc
  • Scope of Variables
             -------------------------------------------------
            total = 0; # This is global variable.
            # Function definition is here
            def sum( arg1, arg2 ):
            # Add both the parameters and return them."
            total = arg1 + arg2; # Here total is local variable.
            print "Inside the function local total : ", total
            return total;
            # Now you can call sum function
            sum( 10, 20 );
            print "Outside the function global total : ", total 
            -----------------------------------------------------------
  • Modules
            import mod1 => importing mod1.py (Refer pdf)
  • INPUT/OUTPUT

           s = raw_input("enter something")
           print "you entered:", s

           s = input("enter something")
           print "you entered:", s
  • Opening and Closing Files
           fo = open("c:/testing.txt", "r")
           str = "qqqq"
           while(str):
           str = fo.next()
           print str
           fo.close()
  • Exceptions
            try:
            fh = open("testfile", "w")
            fh.write("This is my test file for exception handling!!")
            except:
            # except IOError:
            print "Error: can\'t find file or read data"
            else:
            print "Written content in the file successfully"
            fh.close()
 
           ------------------------------------------------------------------------------------
 
Edited

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