Python
What is it?
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Python is a programming language.
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It is an interpreted language which executes line by line.
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It is used for web development (server-side), software development, mathematics, system scripting.
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Used on a server to create web applications and can connect to database systems.
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It can also read and modify files.
History
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It was created in 1991.
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Designed by Guido van Rossum. (worked in Google & Dropbox)
Uses
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Automatic Task
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Make a game
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Real-world problems
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Server-client web development.
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General purpose software.
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Embedded software.
Why
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Python was designed to for readability.
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Python works on different platforms.
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Python can be treated in a procedural way, an object-orientated way or a functional way.
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One line code for swapping values; x,y = y,x
Cross-compilers to other languages
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There are several compilers to run the python program on different platforms.
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Here are some examples:
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Jython compiles into Java bytecode, and execute on Java Virtual Machine.
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IronPython is to run Python programs on the .NET Common Language Runtime.
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Pyjs compiles Python to JavaScript.
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Cython compiles Python to C and C++.
Python Installation
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To check if you have python installed on a Windows PC:
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Run the following on the Command Line (cmd.exe), python --version
There is no Python installed on the PC.
Type python - -version
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We can download it for free from the following website: https://www.python.org/
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Open the .exe installer file.
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Make sure you tick the "Add Python 3. to PATH" checkbox and click on "Install Now",
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Verify the installation was successful by opening a command prompt and running the python command.
Type python - -version
Python installed on the PC.
The Hello World
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Python is an interpreted programming language.
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We need to write Python (.py) files in a text editor and then put those files into the python interpreter to be executed.
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Where HelloWorld.py is the name of your python file.
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We wrote the one line program in a text editor.
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Save the python file, navigate the path on the command line.
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To run the file, type python helloworld.py
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The the print line shows here.
To run the python file
Here is the output.
Python Command Line
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After running the Python command, the prompt changed to >>>
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For a quick test, we can type commands (code) into the Python prompt results in answers in Python.
To pring the string
Operator
Operator & String
Python function
We got our first error
Python Command Line
Setting up Python with Sublime
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To write the python program with Sublime Text 3 editor and make the editor compatible with python codes, here are some steps:
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On Sublime Text, go to Tools > Command Pallets > type Install-Package Controller > click to install.
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Type and install SublimeREPL or Python 3.
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This plug-in lets the user to an interactive interpreter for several languages.
Install the Python 3 plug-in
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For command line output in the editor, go to Tools > Built System > select Python.
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Hit Ctrl + B or Tool menu > Build for command line output.
Coding window
Command line wondow
(output)
Python Syntax
Indentations in Python
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Python uses indentation to indicate a block of codes.
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It gives an error if no indent in a block.
Indentation
No-Indentation
Comments
Variable Declaration
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Python has no command for declaring a variable.
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The variable is being declared when we assign a value.
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The right side of the = operator is being assigned to a variable.
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The variable type keeps changing after re-assign.
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Varible name should start with alphabet or underscore & can contain numbers, alphabets or underscore.
Variable declaration
Datatypes
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The data stored in memory can be any types.
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To verify the type of an object in Python, use the type( ) function:
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Here are some Python datatypes.
Datatypes
Number
stores number
String
"char"
List
['a','b','c']
Tuple
('a', 'b', 'c')
Dictionary
{'key' : 'value'}
value can't change
Integer
100
Float
100.12
Complex
5j, 3=4j
Number
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Number objects are created when you assign a value.
String:
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Stores number of character.
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In Python, 'hello' is the same as "hello".
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Subsets of strings can be taken using the slice operator ([ ] and [ : ] ) with index.
List [ ]
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Lists are the most versatile of Python's compound data types. (multiple datatypes)
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A list contains items separated by commas and enclosed within square brackets [ ].
Tuple ( )
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Unlike List, the value in a tuple cannot be changed.
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It is a read-only List.
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It is enclosed within parentheses.
Dictionary { }
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Dictionary is a kind of hash table type.
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It is a collection which is unordered, changeable and indexed.
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It is also possible to use the dict() constructor to make a dictionary.
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There is some function for accessing & manipulating the string, tuple, list, and dictionary.
Type Casting
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We can specify a type on to a declared variable.
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Casting in python are done using some below functions:
Operator
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Operators are used to perform some operation to a variable.
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Similar to another program, Python has different types of operators as follows:
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Arithmetic operators ( + - * / % ** // )
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Assignment operator ( = += -= %= >>= |= ^= )
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Comparison operator ( == != < > >= <= )
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Logical operator ( and or not )
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Identity operators ( is is not )
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Membership operators ( in not in )
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Bitwise operator ( & | ^ ~ << >> )
Conditional Statement
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Python supports comparison operator to make a condition.
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Thes conditions can be used in a loop and if condition.
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On condition we need to use indentation for the code.
if statement
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if the keyword is used to execute some code in a specific condition.
if elif statement
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elif keyword is used in python, if the previous conditions were not true, then do this condition.
if else statement
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If all the previous conditions were false, then perform else statement.
Loop control statement
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For iteration, there are 2 loop in python:
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For Loop: Iterates the statement for a limited time, when the condition is true.
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While Loop: The statements are being executed unless the given condition is false.
// For loop
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In Python, else statement can be associated with while and for loop.
// While loop
// While - else
Loop control statement
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Inside a loop, python has 3 statement to control the loop:
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pass: When we have no statement to pass.
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continue: To skip the rest of the body of the loop, and continue iterating.
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break: Terminates the loop statement and transfers execution to the statement immediately.
// continue
// break
1st loop
2nd loop
Programing Concept
function
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A Function is a block of code runs only when it is called.
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We can pass parameter (value or reference).
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The function block starts with def keyword followed by the function name and parentheses( ).
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And the function block indented after column :
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The function can return a value.
module
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Like a library, a module is a file (.py) consisting of Python code; classes, functions & variable.
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We can use that module in our application by import keyword followed by module name.
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While python interpreter gets import statement it looks for the corresponding module file here:​
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Current path
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Shell variable path
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Default path: C:\Users\SPS\AppData\Local\Programs\Python
Built-in Module
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Python comes with some built-in modules. (eg. sys, io, platform)
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For easy work, we can import those.
User-defined Module
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A user can make a module by having the required variable, function and classes.
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Save the file as .py extension, and keep in the current path.
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And use those functions, value form that python file.
Python Package Manager
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Python has a Package manager for downloading different the modules.
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The later version of Python 3.4 has installed pip.
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Here how to install a package:
To download & install camelcase module
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Once the package is installed we can use that.
File I/O Handling
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Python provides 2 functions to get the user input.​
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raw_input ( )
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input( )
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We can create, read, update & delete the files using some functions.
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The open( filename, mode ) function takes two parameters; filename, and mode.
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r : Read
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a : Append
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w : Write
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x : Create
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For handing mode of file:
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t: Text mode
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b: Binary mode
Write File
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Here is an example of writing a file.
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The text file gets affected as below.
Read File
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In python, open( ) function returns a file object, where it has a read( ) function is used to read the content.​
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Here is the example for reading the text file data as string.
Exersice: Read the 2nd and 4th line of the file.
OS Module
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The is os module which allows us to remove the file and rename the file as well.
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ps.remove("note.txt") : Remove a file in local directory.
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os. rename("old.txt","new.txt") : Rename a file
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os.mkdir("Folder1") : Make a new folder.
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os.getchwd( ) : Get the current working directory.
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os.chdir("/Folder/SPS/qPlus") : To chage the current working directory.
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Python & MySQL
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We can use Python in a database application.
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Here we have MySQL database installed to work with.
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We can choose any database for our application.
MySQL Driver
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In order to work with a MySQL database in Python, we need to install a driver for respective database.
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MySQL Connector is the driver we are going to intall on PIP.
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We can download and install the driver from the internet.
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Open the PIP path in CMD > type python -m pip install mysql -connector
Download & Install the mysql connector on pip
Create Connection
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After installing the driver, we can create a connection,
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We need to import module, create a connection object with a database credential.
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A short program for testing the connection between Python and MySQL.
Connection established.
SELECT Table
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To run any query on database, we need to create a cursor class object.
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The cursor object allows us to run the query & handle the returned record.
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In the MySQL database, we have the following data in a database.
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There are some functions to getting the record from the database on below.
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cursor.fetchall ( ) - Returns all rows from executed records.
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cursor.fetchone ( ) - Returns only one row.(first row)​​
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Here is a program for SELECT query and getting the records.
SELECT Table
INSERT Table
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To insert the data from Python to MySQL can be done using by following steps.
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First: Call the execute ( ) function with query & data as an argument.
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Second: Call commit ( ) function for making changes on database.
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For inserting to database functions are:
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cursor.execute (sql query , data) - For inserting one-row
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cursor.executemany (sql query, data_Tuple) - For inserting multiple rows.
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dbConn.commit ( ) - For saving the chages.
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INSERT Table
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The GIF shows how it works after executing the above python program & checked on MySQL database.
Excel To Database
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Here we are going to import excel files in Python and write those spreadsheet data into databse.
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There are several modules available for work with a spreadsheet.​
Data
Excel
python
Data
mySQL Databse
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In this case, we will download and install xlrd module.
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To do so, open CMD > type and enter pip install xlrd
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The below program is for importing a excel file from the local directory.
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And inserting to MySQL database.
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After running the python program, the 4 rows are been updated to database.
Python Graphics
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For graphic work, there are several modules we can put on to work in python.
Python Turtle
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Turtle is a python module for drawing comes with python package.
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All we need to import the module, make an instance, draw a shape, and put on the screen.
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Here is the following steps on below.
Turtle Function
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Here are some turtle functions of turtle module for drawing.
Exercise
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Draw a circle, line, rectangle & star.
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Output:
Programs
Program 1
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Finding the first non-repeated character in String.
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Input: stonepfofits
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Output: n
Program 2
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Find the Permutation of string.
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Input: ab
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Output: ab, ba
Program 3
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Find Digit Identification if the string has any number.
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Input: Stone123Profits
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Output: True, if the string contains a number; False, if the string contains a number
Program 4
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Find and Replace the 1st highest repeated character with user given character.
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Input: abcabab
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Output: pbcpbpb
Program 5
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Write a program to print Diamond pattern.
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Input: 5
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Output: pattern
Program 6
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Write a program to sum the numbers in a string.
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Input: stone123profits7
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Output: 130
