Python unit 2 as per Anna university syllabus

Unit 2Unit 2
DATA , EXPRESSIONS, STATEMENTS
S.DHIVYA,AP/CSE
KONGUNADU COLLEGE OF
ENGINEERING AND TECHNOLOGY
KONGUNADU COLLEGE OF
ENGINEERING AND TECHNOLOGY

Python Programming History
It was created by Guido Van Rossum ,
python is derived from many other language
including ABC , Modula 3, C , C++ , Algol-68 ,
Small talk , Unix. It got name from “Monty
Python Flying Circus”.
‘python’ is a general purpose interpreted ,
interactive , object oriented ,and high level
language,
Released in 1991, it support both 32 and
64 bit integers and wordsize.
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Python is High level language:
It is look like a normal English. It is most
compatible with human language.
Python is interpreted:
Python is processed at run time by the
interpreter, you do not need to compile your
program before executing it.
Python support Object –Oriented,
Python is a beginners language.
Python is interactive :
you can type into python prompt and interact
with the interpreter directly to write the program.
Advantages
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Features and application of ‘python’
languages
• Python is general purpose ,structured
programming language.
• Easy to learn.
• Easy to maintain.
• Free and open source.
• High level language.
• Extensive libraries.
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Why we need python
• Software quality
• Developer productivity
• Support library
• Enjoyment
• Program portability
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PYTHON INTERPRETER
Source code
Input data
Interpreter
Output
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Interpreter:
An interpreter processes the program a little at a time ,
alternatively reading lines and performing computation.
python Analyze and Executes program statements at the same
time ,
Overall Execution time is high,
Easier to debug the program.
There are two ways use interpreter:
1. Interactive mode - In this to type the program then press enter and
the interpreter displays the result.
>>> 2+2
>>> 4
The chevron , >>> is the prompt the interpreter uses to indicate that it is
ready.
2. Script mode:
If you type multiple statement into a file and save with .py
extension , then the interpreter execute the file is called a script,
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Interactive mode
• The interpreter provides an interactive
environment to play with the language
• Results of expressions are printed on the
screen
>>> 3 + 7
10
>>> 3 < 15
True
>>> 'print me'
'print me'
>>> print 'print me'
print me
>>>
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Interpreter Vs Compiler
Interpreter Compiler
Translates program one statement at a
time.
Scans the entire program and translates it
as a whole into machine code.
It takes less amount of time to analyze the
source code but the overall execution time
is slower.
It takes large amount of time to analyze
the source code but the overall execution
time is comparatively faster.
No intermediate object code is generated,
hence are memory efficient.
Generates intermediate object code
which further requires linking, hence
requires more memory.
Continues translating the program until
the first error is met, in which case it
stops. Hence debugging is easy.
It generates the error message only after
scanning the whole program. Hence
debugging is comparatively hard.
Programming language like Python, Ruby
use interpreters.
Programming language like C, C++ use
compilers.
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Values and Types
Values:
• A value is one of the fundamental things like
word or a number that a program manipulate.
Types:
– Integer
– Float
– Booleans
– String
– List
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Integer & Float
• Integer – whole numbers
Ex: a = 10
b = -25
• Float – floating point values
Ex:
a=6.5
b=10.14
• To view the type of data:
>>> c=64
>>> type(c)
<type int>
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Boolean
• A Boolean variable can take two values
True
False
Ex:
>>> 34>64
False
>>> 68>45
True
>>> test=(45>32)
>>> test
True
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Strings
• Set of characters represented in quotation marks,
either single or double quotes.
• Subsets of string can be taken by using the slice
operator[:] with index 0 is starting.
Character:
• It is a single alphabet represented by single, double
or trible quotes.
Ex: ‘a’ or “a” or ‘“a’’’
String:
• It is represented by more than one character within
single, double or trible quotes.
Ex: ‘Hi’ or “Hi” or ‘“Hi’’’
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Operator on strings:
‘+’ and ‘*’
>>> ‘horse ’ + ‘and ’ + ‘dog’
horse and dog
>>> “#” * 5
#####
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String operations
• Find() – to find whether the given character is
present in the string or not
• Ex:
>>> a=“hello world”
>>> print(a.find(“w”))
>>> 6
• Split() – to split the strings
• Ex:
>>> print(a.split(“ ”))
(‘hello’,‘world’)
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• Slicing – to view particular character or string
Ex: >>> print(a[6:12])
world
• Strip() –to remove a string
Ex: >>> print(a.strip(“hel”))
o world
• lstrip() –to remove the first character from the
string
Ex: >>> print(a.lstrip(“h”))
ello world
>>> b=‘44444hihello222’
>>> print(b.lstrip(‘4’))
hihello222
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• upper() – to convert the strings into uppercase
Ex: >>> d=“welcome”
>>> print(d.upper())
WELCOME
• lower() - to convert the strings into lowercase
EX: >>> e=“PYTHON”
>>> print(e.lower())
python
• String Concatenation (+) – to add two strings
Ex: >>> ‘how ’ + ‘are ’ + ‘you’
>>> how are you
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String Reverse
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List
• A list contains items separated by commas and
enclosed with square bracket [ ] .
• List and arrays are same in python.
• values stored in list is accessed by using its index
or its value by slicing.
>>> List_name=[ ] - empty list
>>> List=[“ram”,31,54,12,47]
>>> list
[“ram”,31,54,12,47]
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List – Operations
• To View a particular value in a list
>>> d=[“hi”,34,64,“rani”,12]
>>> print(d[2])
64
• Update() – to update a value in a list
>>> L1=[10,11,12,13,15]
>>> L1[4]=14
>>> L1
[10,11,12,13,14]
• Delete() – to delete a value from a list
>>> del L1[2]
>>> L1
[10,11,13,14]
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• len() – to find the length of a list
>>> len(L1)
4
• Concadenate
>>> [1,2,3] + [4,5,6]
[1,2,3,4,5,6]
• Append() – to add a new value at last of a list
>>> L2=[‘eat’, ‘more’, ‘fruits’]
>>> L2.append(‘daily’)
>>> L2
[‘eat’, ‘more’, ‘fruits’, ‘daily’]
>>> L2.append([‘aaa’,23]) – to append a new list
[‘eat’, ‘more’, ‘fruits’, ‘daily’,[‘aaa’,23]]
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• Extend() – to add a list of elements
>>> L2.extend([‘hi’,43])
>>> L2
[‘eat’, ‘more’, ‘fruits’, ‘daily’,[‘aaa’,23],‘hi’,43]
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• Slicing in list:
>>> list=["ram",54,64,78]
>>> print(list[2:3])
[64]
>>> print(list[:])
['ram', 54, 64, 78]
>>> print(list[:3])
['ram', 54, 64]
>>> print(list[3:])
[78]
>>> print(list[1:3])
[54, 64]
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Variables
• A variable is nothing but a reserved memory
location to store values.
• Ex:
>>> a=5 // integer variable
>>> print (a)
5
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Rules for naming variable
• Variable can be combination of uppercase,
lowercase, underscores(_) and digits(0-9).
• Special characters not allowed within
identifier.
• An variable not begin with numbers.
• Python keyword not used as a identifier.
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Local and Global variable
• Local variable:
a variable which is declared inside a
function is called as local variable.
• Global variable:
a variable which is declared outside a
function is called as global variable.
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Expression
• Expression is the combination of variables
and constants are interconnected with
operators.
• Syntax: variable = expression
• Ex: d = (a+b*c)
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Statements
• It is an instruction which is executed by
python interpreter.
@ Print
@ Assign
>>> x=2 # assigning a value
>>> print(x) # print statement
2
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Multiline statements
>>> a=1
>>> b=2
>>> sum=a+
b
>>> print(sum)
3
Multiline statement in a single line by using (;)
>>> c=5;d=6;sum=c+d;print(sum)
11
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Tuple Assignment
• Tuple contains items separated by commas and
enclosed with parenthesis().
• Values cannot be edit or update, insert a new value in
Tuple.
Ex: >>> tuple1=(“ram”,54,656,50)
>>> print(tuple1)
‘ram’,54,656,50
>>> print(tuple1[0])
‘ram’
>>> print(tuple1[1:3])
54,656
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Precedence of operator
• High : / * %
• Low : + -
Ex:
workout this expression and write correct answer
3 - 12/3 + 77 * 3 - 1
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Comments
# sign used to write comment line in between the programs.
Cannot be executed.
Types :
– Single line
– Multi line
Single line:
Single line comment starting with # symbol
Ex:
# This is a sample example
a=10
# The value 10 is assigned to a variable
print(a)
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Output:
10
Multi line:
Multi line comment starting with # symbol
Ex:
# This is a sample
# to print a string
print(“hello”)
Output:
hello
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Module
• a module is a file consisting of Python code. A
module can define functions, classes and variables.
A module can also include runnable code.
Example:
Here's an example of a simple module, support.py
def print_func( par ):
print ("Hello : ", par )
return
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Python unit 2 as per Anna university syllabus

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