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PYTHON PROGRAMMING III YEAR/II SEM

PYTHON PROGRAMMING

LECTURE NOTES

DEPARTMENT OF

COMPUTER SCIENCE AND ENGINEERING

MALLA REDDY COLLEGE OF ENGINEERING &

TECHNOLOGY

PYTHON PROGRAMMING III YEAR/II SEM

SYLLABUS

MALLA REDDY COLLEGE OF ENGINEERING AND TECHNOLOGY III Year B. Tech CSE -II SEM L T/P/D C 3 - / - / - 3 OPEN ELECTIVE III (R17A0554) PYTHON PROGRAMMING OBJECTIVES:  To read and write simple Python programs.  To develop Python programs with conditionals and loops.  To define Python functions and call them.  To use Python data structures – - lists, tuples, dictionaries.  To do input/output with files in Python. UNIT I INTRODUCTION DATA, EXPRESSIONS, STATEMENTS Introduction to Python and installation , data types: Int, float, Boolean, string, and list; variables, expressions, statements, precedence of operators, comments; modules, functions--- function and its use, flow of execution, parameters and arguments. UNIT II CONTROL FLOW, LOOPS Conditionals: Boolean values and operators, conditional (if), alternative (if-else), chained conditional (if-elif-else); Iteration: while, for, break, continue. UNIT III FUNCTIONS, ARRAYS Fruitful functions: return values, parameters, local and global scope, function composition, recursion; Strings: string slices, immutability, string functions and methods, string module; Python arrays, Access the Elements of an Array, array methods. UNIT IV LISTS, TUPLES, DICTIONARIES Lists: list operations, list slices, list methods, list loop, mutability, aliasing, cloning lists, list parameters, list comprehension; Tuples: tuple assignment, tuple as return value, tuple comprehension; Dictionaries: operations and methods, comprehension;

UNIT V FILES, EXCEPTIONS, MODULES, PACKAGES Files and exception: text files, reading and writing files, command line arguments, errors and exceptions, handling exceptions, modules (datetime, time, OS , calendar, math module), Explore packages.

PYTHON PROGRAMMING III YEAR/II SEM

INDEX

UNIT TOPIC PAGE NO

I

Conditionals : Boolean values and operators,

• EXPRESSIONS, STATEMENTS INTRODUCTION DATA,
  • Introduction to Python and installation
  • data types: Int
  • float
  • Boolean
  • string
  • List
  • variables
  • expressions
  • statements
  • precedence of operators
  • comments
  • modules
  • functions ----- function and its use
  • flow of execution
  • parameters and arguments
  • CONTROL FLOW, LOOPS II
  • conditional (if)
  • alternative (if-else)
  • chained conditional (if-elif-else)
  • Iteration: while, for, break, continue.
    • FUNCTIONS, ARRAYS III
    • Fruitful functions: return values
    • parameters
    • local and global scope
    • function composition
    • recursion
    • Strings: string slices
    • immutability
    • string functions and methods
    • string module
    • Python arrays
    • Access the Elements of an Array
    • Array methods

PYTHON PROGRAMMING III YEAR/II SEM

IV

LISTS, TUPLES, DICTIONARIES 78

Lists (^78) list operations (^79) list slices (^80) list methods (^81) list loop (^83) mutability (^85) aliasing (^87) cloning lists (^88) list parameters (^89) list comprehension (^90) Tuples (^91) tuple assignment (^94) tuple as return value (^95) tuple comprehension (^96) Dictionaries (^97) operations and methods (^97) comprehension (^102) V FILES, EXCEPTIONS, MODULES, PACKAGES

Files and exception: text files (^103) reading and writing files (^104) command line arguments (^109) errors and exceptions (^112) handling exceptions (^114) modules (datetime, time, OS , calendar, math module)

Explore packages (^134)

Statement

Statement

Script Ends

Differences between scripting language and programming language:

Why to use Python:

The following are the primary factors to use python in day-to-day life:

1. Python is object-oriented Structure supports such concepts as polymorphism, operation overloading and multiple inheritance. 2. Indentation Indentation is one of the greatest feature in python

3. It’s free (open source) Downloading python and installing python is free and easy 4. It’s Powerful  Dynamic typing  Built-in types and tools  Library utilities  Third party utilities (e.g. Numeric, NumPy, sciPy)  Automatic memory management 5. It’s Portable  Python runs virtually every major platform used today  As long as you have a compaitable python interpreter installed, python programs will run in exactly the same manner, irrespective of platform. 6. It’s easy to use and learn  No intermediate compile  Python Programs are compiled automatically to an intermediate form called byte code, which the interpreter then reads.  This gives python the development speed of an interpreter without the performance loss inherent in purely interpreted languages.  Structure and syntax are pretty intuitive and easy to grasp. 7. Interpreted Language Python is processed at runtime by python Interpreter 8. Interactive Programming Language Users can interact with the python interpreter directly for writing the programs 9. Straight forward syntax The formation of python syntax is simple and straight forward which also makes it popular.

Installation:

There are many interpreters available freely to run Python scripts like IDLE (Integrated Development Environment) which is installed when you install the python software from http://python.org/downloads/ Steps to be followed and remembered: Step 1: Select Version of Python to Install. Step 2: Download Python Executable Installer. Step 3: Run Executable Installer. Step 4: Verify Python Was Installed On Windows.

Running Python in interactive mode:

Without passing python script file to the interpreter, directly execute code to Python prompt. Once you’re inside the python interpreter, then you can start.

>>> print("hello world")

hello world

Relevant output is displayed on subsequent lines without the >>> symbol

>>> x=[0,1,2]

Quantities stored in memory are not displayed by default.

>>> x

#If a quantity is stored in memory, typing its name will display it.

[0, 1, 2]

>>> 2+

5

The chevron at the beginning of the 1st line, i.e., the symbol >>> is a prompt the python interpreter uses to indicate that it is ready. If the programmer types 2+6, the interpreter replies 8.

Running Python in script mode:

Alternatively, programmers can store Python script source code in a file with the .py extension, and use the interpreter to execute the contents of the file. To execute the script by the interpreter, you have to tell the interpreter the name of the file. For example, if you have a script name MyFile.py and you're working on Unix, to run the script you have to type:

python MyFile.py

Working with the interactive mode is better when Python programmers deal with small pieces of code as you can type and execute them immediately, but when the code is more than 2-4 lines, using the script for coding can help to modify and use the code in future.

Example:

Data types:

The data stored in memory can be of many types. For example, a student roll number is stored as a numeric value and his or her address is stored as alphanumeric characters. Python has various standard data types that are used to define the operations possible on them and the storage method for each of them.

Int:

Int, or integer, is a whole number, positive or negative, without decimals, of unlimited length.

>>> print(24656354687654+2)

24656354687656

>>> print(20)

20

>>> print(0b10)

2

Example:

x = 35e y = 12E z = -87.7e

print(type(x)) print(type(y)) print(type(z))

Output:

Boolean:

Objects of Boolean type may have one of two values, True or False:

>>> type(True)

>>> type(False)

String:

1. Strings in Python are identified as a contiguous set of characters represented in the quotation marks. Python allows for either pairs of single or double quotes.

• 'hello' is the same as "hello".
• Strings can be output to screen using the print function. For example: print("hello").

>>> print("mrcet college")

mrcet college

>>> type("mrcet college")

>>> print('mrcet college')

mrcet college

>>> " "

' '

If you want to include either type of quote character within the string, the simplest way is to delimit the string with the other type. If a string is to contain a single quote, delimit it with double quotes and vice versa:

>>> print("mrcet is an autonomous (') college")

mrcet is an autonomous (') college

>>> print('mrcet is an autonomous (") college')

mrcet is an autonomous (") college

Suppressing Special Character:

Specifying a backslash () in front of the quote character in a string “escapes” it and causes Python to suppress its usual special meaning. It is then interpreted simply as a literal single quote character:

>>> print("mrcet is an autonomous (') college")

mrcet is an autonomous (') college

>>> print('mrcet is an autonomous (") college')

mrcet is an autonomous (") college

The following is a table of escape sequences which cause Python to suppress the usual special interpretation of a character in a string:

>>> print('a\

....b')

a ... b

>>> print('a\

b\

c')

>>> x=list() >>> x []

>>> tuple1=(1,2,3,4) >>> x=list(tuple1) >>> x [1, 2, 3, 4] Variables: Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.

Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals or characters in these variables. Rules for Python variables:

• A variable name must start with a letter or the underscore character
• A variable name cannot start with a number
• A variable name can only contain alpha-numeric characters and underscores (A-z, 0-9, and _ )
• Variable names are case-sensitive (age, Age and AGE are three different variables)

Assigning Values to Variables: Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables. The operand to the left of the = operator is the name of the variable and the operand to the right of the = operator is the value stored in the variable.

For example −

a= 100 # An integer assignment

b = 1000.0 # A floating point

c = "John" # A string

print (a)

print (b)

print (c)

This produces the following result −

100

John

Multiple Assignment:

Python allows you to assign a single value to several variables simultaneously.

For example :

a = b = c = 1

Here, an integer object is created with the value 1, and all three variables are assigned to the same memory location. You can also assign multiple objects to multiple variables.

For example −

a,b,c = 1,2,"mrcet“

Here, two integer objects with values 1 and 2 are assigned to variables a and b respectively, and one string object with the value "john" is assigned to the variable c.

Output Variables:

The Python print statement is often used to output variables.

Variables do not need to be declared with any particular type and can even change type after they have been set.

>>> x=

>>> y=

>>> c=x+y

>>> c

30

A value all by itself is a simple expression, and so is a variable.

>>> y=

>>> y

20

Python also defines expressions only contain identifiers, literals, and operators. So,

Identifiers: Any name that is used to define a class, function, variable module, or object is an identifier.

Literals: These are language-independent terms in Python and should exist independently in any programming language. In Python, there are the string literals, byte literals, integer literals, floating point literals, and imaginary literals.

Operators: In Python you can implement the following operations using the corresponding tokens.

Operator Token

add +

subtract -

multiply *

Integer Division /

remainder %

Binary left shift <<

Binary right shift >>

and &

or \

Less than <

Greater than >

Less than or equal to <=

Greater than or equal to >=

Check equality ==

Check not equal !=