Python File Handling

File Handling

• File handling describes reading, writing, and manipulating files via Python code.
• Actions include opening, closing, reading, writing, and deleting files.
• File handling enables storing and retrieving data for use in programs.

Opening Files

• The open() function opens files in Python.
• Example: f = open(filename, mode)

File Open Modes

• r: Opens an existing file for reading.
• w: Opens a file for writing; will overwrite existing data or create the file if it does not exist.
• a: Opens a file for appending; to add data without overwriting existing data.
• r+: Opens a file for both reading and writing; overwrites existing data.
• w+: Opens a file for both writing and reading; overwrites existing data.
• a+: Opens a file for appending and reading; does not overwrite existing data.

Writing sample

• A sample program opens data.txt in write mode, prompts the user for content, and writes it to the file.

Appending sample

• An appending sample opens data.dat in append mode, prompts for ID, name, and salary, and appends the formatted data to the file.

Copying sample

• A copying sample prompts for source and target files, then copies the content from one to the other.

Counting sample

• A counting sample opens a file and counts the number of uppercase and lowercase characters.

Advantages of File Handling

• Versatility in creating, reading, writing, appending, renaming, and deleting files.
• Flexibility when working with various file types and operations on files.
• User-friendly interface for easy file manipulation.
• Cross-platform compatibility for seamless integration.

Disadvantages of File Handling

• File handling can be error-prone if the code is not carefully written.
• Security risks arise with user input modifying sensitive files.
• Complexity increases with advanced file formats and operations.
• Performance may be slower than other programming languages, particularly with large files.

CSV Files

• Stands for "Comma Separated Values" and is a plain text file formatted to arrange tabular data.
• Includes printable ASCII or Unicode characters, with commas separating values.

Reading CSV Files

• A reader object is used
• The CSV File must be opened as a text file using open() which returns a file object.

Reading CSV Data Example

• A sample program imports the csv module, then opens a file named username.csv and reads its contents line by line.

Classes

• Classes are user-defined data types bundling data and methods.
• Classes serve as templates for objects and define characteristics and operations.
• Created via the class keyword.

Objects

• An object is a specific instance of a class, with unique characteristics and functions.
• Objects can be made once a class is established.
• The object's attributes are initialized in the _init_ constructor.

Class and Object Sample

• A sample program defines a class Person with name, age, and a greet method, then creates a Person object named person1 and calls its greet method.

Constructors

• A constructor is a special method for initializing instance members of a class.
• They come in Parameterized and Non-parameterized types
• Executed when the object of a class is created.

Constructor Sample

• The constructor assigns Employee id and name
• The display function prints the employee details

Inheritance

• Inheritance is a crucial aspect of object-oriented programming.

Inheritance Feature

• Enables code reusability by creating new classes from existing ones.
• Allows child classes to acquire properties and access data members and functions from parent classes.
• Permits child classes to provide specific implementations for parent class functions.
• A derived class can inherit a base class by adding a base class in brackets

Advantages of Inheritance

• Improves code reusability therefore removing the need to re-write code.
• Programmers don't need to write the same code and logic therefore reducing coding efforts.
• More concise and structured programs improve the readability of code.

Sample One-level

• Two inherits parent class One

Multi-Level Inheritance

• Achieved when a derived class inherits another derived class, making it possible in Python.
• There is no limit on levels.

Multi-Level Sample

• C (child) inherits from B (middle), which inherits from A (parent)

Multiple Inheritance

• One class inherits from multiple other classes at the same time

Sample: Multiple Inheritance

• Derived Class inherits from Calculation 1 and Calculation 2 to perform summation multiplication

Abstraction

• Abstraction hides internal functionality from users.
• Allows users to focuses on implementation
• Increases Effiency

Abstraction Classes

• An abstract class contains on or more abstract methods
• Abstract classes are a meant to be the blueprint for other classes
• Useful when designing large functions for implementing standard interfaces.

Abstraction Sample

• Several classes inherit from the car class to abstract mileage information

Polymorphism

• Means "having multitude of forms"
• Makes function names reusable across multiple types

Polymorphism sample

• add() adds two or three inputs

Threads

• Threads represent separate independent line of code to be ran
• Python Vitrual Machine executes them
• PVM always uses one thread internally

Threading

• Module needs importing
• Shows the current thread

Multithreading

• Divides a main task into sub-tasks that are executed in an overlapping manner.
• Allows for faster execution.
• Each process gets separate memory space
• Threads of the same program share the same memory allocation

Benefits of Multithreading using Python

• Usage of PC framework is more powerful
• Applications respond faster
• More cost effective due to sharing of resources
• Makes Multiprocessor Engineering more viable
• Cuts down on time due to running multiple threads simultaneously
• System doesn't require lots of memory

Threading Module Methods

• threading.activeCount(): Returns the active number of objects.
• threading.currentThread(): Returns the number of thread objects controlled.
• threading.enumerate(): Returns a list of all active thread objects.
• run(): Is the entry point for a thread.
• start(): Starts a thread by calling the run method.
• join([time]): Waits for threads to terminate.
• isAlive(): Checks whether a thread is still executing.
• getName(): Returns the name of a thread.
• setName(): Sets the name of a thread.

Creating Threads

• Using the Thread module
• Create an object of the Thread class

Without a Class

• Run a group of statements using a function
• Create a thread object
• The target represents the function being implemented

Without a Class Example Code

• Creates a thread to run the function display 5 times

Using a Sub Class to Thread Class

• Able to subclass Thread to inherit its functionality
• Here MyThread is a subclass
• Run() is made accessible to subclasses
• Threads implemented with run()
• Object created of MyThread

Using a Sub Class to Thread Class Example Code

• Creates MyThread and performs tasks

Without Creating Sub Class to Thread Class

• Run display() Method

Without Creating Sub Class to Thread Class Example Code

• Runs the thread and code

Thread Synchronization

• Shows how to use and execute multiple tasks
• Demonstrates joining

Thread Synchronization Example Code

Networks

• Networks are a group of interconnected computers.
• Uses cables
• Internet represents the largest network.
• Used to share resources and information
• hardware also share CPU among uses
• No need for extra hardware like printers

Network requirements

• Hardware such as computers, cables, modems, routers, hubs
• Software to communicate between clients and servers
• Protocol to connect and establishes data sending

Protocol is Rules

• Protocol is a set of rules followed by networks
• Uses TCP/IP and UDP

Data handling protocol

• Breaking down files to transmit
• Using TCP/IP and UDP

TCP Protocol Info

• TCP(Transmission Control Protocol) and IP(Internet Protocol) is standard
• Transfers date across networks

###UDP Protocol Info

• Another way to send data across connections
• Less reliable as It skips checking bit transfers
• Data can be lost

Sockets

• Sockets act as a way for communication for local / remote machines
• Unix sockets act as read/write files but sends data across the network
• Sockets use IP addresses and ports

Find IP Address

• Uses gethostbyname() function
• Shows address or errors

Knowing IP Address Example Code

• Finds Google's IP adress

TCP/IP Server

• Programs provides services to other computers
• Uses a Client
• Requires a socket for the connection

TCP/IP Server Steps

• Create a TCP/IP socket at server end with socket.AF_INET, socket.SOCK_STREAM
• Bind the socket with host name using bind()
• Specify max connections
• Waits on clients using accept()
• Sends messages using send()
• Server can disconnect with c.close()

TCPIP Server Sample

• Sends messages to clients

A TCP/IP Client

• Clients receive data or services from the server.
• Create a socket object using s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
• Connect the socket using the connect method. s.connect((host, port));
• Recv() to receive
• close() to disconnect

TCPIP Client Sample

Tkinter

• Python package
• It's cross-platform, so the same code works on Windows, macOS, and Linux.
• It is one of the only GUI frameworks that is built into standard library

Use cases of Tkinter

• Creating a window or dialog box with Labels and Buttons
• Build a GUI for interactive elements (checkboxes)
• Make command line program interactive with command and bind functions
• Customize widgets for custom widgets with the correct classes
• prototype GUI

Root Window

• Provides display output
• Is called 'top level window' or 'root window'
• Implemented with tkinter import*

Root Window Sample

• Shows how to use Tk() and mainloop()

Program to take input to Lebel Example

• Uses the widgets to show functionality

Containers

• Used as a component where drawings/widgets are displayed
• displays the output to the user
• Has Canvas that draws shapes
• Has Frame which allows widgets such as buttons to be viewed

Canvas Info

• A container to draw shapes

Canvas Sample

Canvas Info

• Used to demonstrate arch shapes

Canvas Sample for Arcs

• Various styles are utilized

Frame details

• Similar to canvas but displays widgets or text in rectangular shape
• Our root window is the frame
• Set with properties

Frame Info

• Provides a container to create event handlers

Frame Sample

Data Base Connectivity

• Data can be stored via Files or Databases
• Databases come with DBMS software

Pythons' Database Types

• Python can connect to: MySQL, Oracle, Microsoft SQL Server, Sybase, Informix, Firebird, IBM DB2, Ingres, PostgreSQL, SAP DB (MaxDB), and Microsoft Access.

Sample to Check Connection

Database Connectivity Sample

• Uses MySQL, displays the info

Retrieving Info

• Displays the employee table in Rows

Retreving Table Sample

• Uses the method fethcall() and cursor to retrieve data

Insert query

• A SQL query is prepared to add a single row to the table
• Commit is called and saved
• Rollback implements during errors

Insert Into Table Sample Code