Python Data Persistence

With SQL and NOSQL Databases

Malhar Lathkar

• Publisher: BPB Publications
• Year: 2019
• eBook ISBN: 9789388511759
• Topic: Computer Science
• Subtopic: Programming in Python
• Index: Computer Science

Designed to provide an insight into the SQL and MySQL database concepts using python. Key Features

• A practical approach
• Ample code examples
• A Quick Start Guide to Python for beginners

Description
Python is becoming increasingly popular among data scientists. However, analysis and visualization tools need to interact with the data stored in various formats such as relational and NOSQL databases.
This book aims to make the reader proficient in interacting with databases such as MySQL, SQLite, MongoDB, and Cassandra.
This book assumes that the reader has no prior knowledge of programming. Hence, basic programming concepts, key concepts of OOP, serialization and data persistence have been explained in such a way that it is easy to understand. NOSQL is an emerging technology. Using MongoDB and Cassandra, the two widely used NOSQL databases are explained in detail.
The knowhow of handling databases using Python will certainly be helpful for readers pursuing a career in Data Science. What Will You Learn

• Python basics and programming fundamentals
• Serialization libraries pickle, CSV, JSON, and XML
• DB-AP and, SQLAlchemy
• Python with Excel documents
• Python with MongoDB and Cassandra

Who This Book Is For
Students and professionals who want to become proficient at database tools for a successful career in data science. Table of Contents

• Getting Started
• Program Flow Control
• Structured Python
• Python – OOP
• File IO
• Object Serialization
• RDBMS Concepts
• Python DB-API
• Python – SQLAlchemy
• Python and Excel
• Python – PyMongo
• Python – Cassandra
• Appendix A: Alternate Python Implementations
  Appendix B: Alternate Python Distributions
  Appendix C: Built-in Functions
  Appendix D: Built-in Modules
  Appendix E: Magic Methods
  Appendix F: SQLite Dot Commands
  Appendix G: ANSI SQL Statements
  Appendix H: PyMongo API Methods
  Appendix I: Cassandra CQL Shell Commands About the Author
  Malhar Lathkar is an Independent software professional / Programming technologies trainer/E-Learning Subject matter Expert. He is a of Director Institute of Programming Language Studies, having an academic experience of 33 years. His expertise is in Java, Python, C#, IoT, PHP, databases. linkedIn: linkedin.com/in/malharlathkar Blog: indsport.blogspot.com
  

CHAPTER 1

Getting Started

Python is very easy to learn. Well, it is also very easy to start using it. In fact I would encourage trying out one of the many online Python interpreters, get yourself acquainted with the language before going on to install it on your computer.

There are many online resources available to work with Python. Python’s official website (https://www.python.org) itself provides online shell powered by http://www.pythonanywhere.com.

Online Python shells work on the principle of Read, Evaluate, Print, Loop (REPL). Such an online Python REPL is available at https://repl.it/languages/python3. It can be used in interactive and in scripting mode.

1.1 Installation

Python’s official website hosts official distribution of Python at https://www.python.org/downloads/. Precompiled installers as well as source code tarballs for various operating system platforms (Windows, Linux, and Mac OS X) and hardware architectures (32 and 64-bit) are available for download. The bundle contains Python interpreter and library of more than 200 modules and packages.

Precompiled installers are fairly straightforward to use and recommended. Most distributions of Linux have Python included. Installation from source code is little tricky and needs expertise to use compiler tools.

Currently, there are two branches of Python software versions (Python 2.x and Python 3.x) on Python website. At the time of writing, latest versions in both branches are Python 2.7.15 and Python 3.7.2 respectively. Python Software Foundation (PSF) is scheduled to discontinue supporting Python 2.x branch after 2019. Hence it is advised to install latest available version of Python 3.x branch.

It is also desirable to add Python’s installation directory to your system’s PATH environment variable. This will allow you to invoke Python from anywhere in the filesystem.

It is now time to start using Python. Open Windows Command Prompt terminal (or Linux terminal), type ‘python’ in front of the prompt as shown below: (Figure 1.1)

Figure 1.1 Python Prompt

If a Python prompt symbol >>> (made up of three ‘greater than’ characters) appears, it means Python has been successfully installed on your computer. Congratulations!!!

Most Python distributions are bundled with Python’s Integrated Development and Learning Environment (IDLE). It also presents an interactive shell as shown in Figure 1.1. Additionally, it also has a Python aware text editor with syntax highlighting and smart indent features. It also has an integrated debugger.

1.2 Interactive Mode

The >>> prompt means that Python is ready in REPL mode. You can now work with Python interactively. The prompt reads user input, evaluates if it is a valid Python instruction, prints result if it is valid or shows error if invalid, and waits for input again. In this mode, Python interpreter acts as a simple calculator. Just type any expression in front of the prompt and press Enter. Expression is evaluated with usual meanings of arithmetic operators used and result is displayed on the next line.

Example 1.1

>>> 5-6/2*3

-4.0

>>> (5-6/2)*3

6.0

>>>

Python operators follow BODMAS order of precedence. There are few more arithmetic operators defined in Python. You will learn about them later in this chapter.

You can assign a certain value to a variable by using ‘=’ symbol. (What is variable? Don’t worry. I am explaining it also later in this chapter!) However, this assignment is not reflected in next line before the prompt. The assigned variable can be used in further operations. To display the value of variable, just type its name and press Enter.

Example 1.2

>>> length=20

>>> breadth=30

>>> area=length*breadth

>>> area

600

Type ‘quit()’ before the prompt to return to command prompt.

1.3 Scripting Mode

Interactive mode as described above executes one instruction at a time. However, it may not be useful when you have a series of statements to be repetitively executed. This is where Python’s scripting mode is used. Script is a series of statements saved as a file with ‘.py’ extension. All statements in the script are evaluated and executed one by one, in the same sequence in which they are written.

The script is assembled by using any text editor utility such as Notepad (or similar software on other operating systems). Start Notepad on Windows computer, enter following lines and save as ‘area.py’

Example 1.3

#area.py

length=20

breadth=30

area=length*breadth

print ('area=',area)

Open the command prompt. Ensure that current directory is same in which ‘area.py’ script (you can call it as a program) is saved. To run the script, enter following command (Figure 1.2):

Figure 1.2 Running Python Script

1.4 Identifiers

Python i...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Preface
• About the Author
• Code Bundle
• Table of Contents
• 1. Getting Started
• 2. Program Flow Control
• 3. Structured Python
• 4. Python - OOP
• 5. File IO
• 6. Object Serialization
• 7. RDBMS Concepts
• 8. Python DB-API
• 9. Python - SQLAlchemy
• 10. Python and Excel
• 11. Python – PyMongo
• 12. Python - Cassandra
• Appendix A: Alternate Python Implementations
• Appendix B: Alternate Python Distributions
• Appendix C: Built-in Functions
• Appendix D: Built-in Modules
• Appendix E: Magic Methods
• Appendix F: SQLite Dot Commands
• Appendix G: ANSI SQL Statements
• Appendix H: PyMongo API Methods
• Appendix I: Cassandra CQL Shell Commands