Python

[seminar class]

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PYTHON
INTRODUCTION
Python is an easy to learn, powerful programming language. It has efficient high-level data structures and a simple but effective approach to object-oriented programming. Python's elegant syntax and dynamic typing, together with its interpreted nature, make it an ideal language for scripting and rapid application development in many areas on most platforms.
The first version was developed by GuidoVan Rossum in 1991
Why not Perl?
 When compared to Perl, Python programs are definitely simpler, clearer, easier to write and hence more understandable and maintainable.
 If you didn't know already, Perl is another extremely popular open source interpreted programming language.
Features of Python
 Simple
 Easy to Learn
 Free and Open Source
 High-level Language
 Portable
 Interpreted
 Object Oriented
 Extensible
 Embeddable
 Extensive Libraries
BASICS
 Literal Constants
 Numbers
1. Integers
2. floating point
3 . complex numbers
 Strings
Variables
 Identifier Naming
àRules
 Data Types
 Objects
 In PYTHON we doesnot declare variables we will just assign to them and go
Operators
 Note that you can evaluate the expressions given in the examples using the interpreter interactively. For example, to test the expression 2 + 3, use the interactive Python interpreter prompt:
>>> 2 + 3
5
>>> 3 * 5
15
>>>
 Operators mainly used
Control Structures
 The if statement
The if statement is used to check a condition: if the condition is true, we run a block of statements (called the if-block), else we process another block of statements (called the else-block). The else clause is optional
à elif(elseif)
 The while Statement
The while statement allows you to repeatedly execute a block of statements as long as a condition is true. A while statement is an example of what is called a looping statement. A while statement can have an optional else clause.
Control Sturctures
 The for loop
The for..in statement is another looping statement which iterates over a sequence of objects i.e. go through each item in a sequence
 Example
for i in range(1, 5):
print(i)
else:
print('The for loop is over')
Control Structures
 The break Statement
The break statement is used to break out of a loop statement i.e. stop the execution of a looping statement, even if the loop condition has not become False or the sequence of items has not been completely iterated over.
The continue Statement
The continue statement is used to tell Python to skip the rest of the statements in the current loop block and to continue to the next iteration of the loop.
Functions
 Functions are reusable pieces of programs. They allow you to give a name to a block of statements, allowing you to run that block using the specified name anywhere in your program and any number of times. This is known as calling the function. We have already used many built-in functions such as len and range.
 Functions are defined using the def keyword. After this keyword comes an identifier name for the function, followed by a pair of parentheses which may enclose some names of variables, and by the final colon that ends the line. Next follows the block of statements that are part of this function.
EXAMPLE FOR FUNCTION
 def sayHello():
print('Hello World!') # block belonging to the function
# End of function
sayHello() # call the function
FUNCTIONS
The return Statement
The return statement is used to return from a function i.e. break out of the function.
 Local variables
 Global variables
Data Structures
 There are four built-in data structures in Python
1.list,
2.tuple,
3.dictionary and
4.set.
CLASSES AND OBJECTS
 class Person:
pass # An empty block
p = Person()
 We create a new class using the class statement and the name of the class. This is followed by an indented block of statements which form the body of the class. In this case, we have an empty block which is indicated using the pass statement.
 Next, we create an object/instance of this class using the name of the class followed by a pair of parentheses.
OBJECT METHODS
 classes/objects can have methods just like functions except that we have an extra self variable
class Person:
def sayHi(self):
print('Hello, how are you?')
p = Person()
p.sayHi()
The __init__ method
 The __init__ method is run as soon as an object of a class is instantiated. The method is useful to do any initialization you want to do with your object.
class Person:
def __init__(self, name):
self.name = name
def sayHi(self):
print('Hello, my name is', self.name)
p = Person('Swaroop')
p.sayHi()
Input Output
 The input() function takes a string as argument and displays it to the user. Then it waits for the user to type something and press the return key. Once the user has entered, the input() function will then return that text
 Print() function helps you to output the text,values of variables
Files
 You can open and use files for reading or writing by creating an object of the file class and using its read, readline or write methods appropriately to read from or write to the file. The ability to read or write to the file depends on the mode you have specified for the file opening. Then finally, when you are finished with the file, you call the close method to tell Python that we are done using the file.
Example of File
 poem = '''\
Programming is fun
When the work is done if you wanna
make your work also fun:
use Python!
'''
f = open('poem.txt', 'w') # open for 'w'riting
f.write(poem) # write text to file
f.close() # close the file
f = open('poem.txt') # if no mode is specified, 'r'ead mode is assumed default
while True:
line = f.readline()
if len(line) == 0: # Zero length indicates EOF
break
print(line, end='')
f.close() # close the file
Handling Exceptions
 We can handle exceptions using the try..except statement. We basically put our usual statements within the try-block and put all our error handlers in the except-block.
 try:
text = input('Enter something --> ')
except EOFError:
print('Why did you do an EOF on me?')
except KeyboardInterrupt:
print('You cancelled the operation.')
else:
print('You entered {0}'.format(text))
Handling Exceptions
 Try .. Finally
Suppose you are reading a file in your program. How do you ensure that the file object is closed properly whether or not an exception was raised? This can be done using the finally block
 The with statement
Acquiring a resource in the try block and subsequently releasing the resource in the finally block is a common pattern. Hence, there is also a with statement
The difference here is that we are using the open function with the with statement - we leave the closing of the file to be done automatically by with open.
APPLICATIONS
 Web and Internet Development
àCGI scripts
 Database Access
àCustom and ODBC interfaces
 Desktop GUIs
 Scientific and Numeric
 Network Programming
àSocket interface
 Game and 3D Graphics
CONCLUSION
 A language will become wide spread if it is simple easy to use and also serves its purpose well ,As PYTHON has all the above mentioned features it is accepted by most of the programmers…