Blueprints: Introduction to Python programming

Blueprints
Bhalaji N
M.Tech., CSE (2016-2018)
Amrita School of Engineering, Coimbatore
You are free to share, modify, copy and use this material and the associated python programs for educational
purposes only.

“Everybody should learn
how to program a
computer because it
teaches you how to
think”
- Steve Jobs

*Data collected from pre-workshop survey

Art of programming
What it takes to be a better computer programmer?

Programming Recipe - Explained
1. Visualization: Program and real word are not two different things. Visualize the
problem as things and don’t see them as programs
2. Relate: Program is just a tool. It is just a way to speak to computers. Relate the
programs to day to day conversations
3. Programming is an art: It is not a skill, it is an art.
4. Cover your basics: Conceptual foundations needs to be strong.
5. Practice: Practice to become a fine artist

Programming Recipe - The perfect blend
Data structures Algorithms
Mathematical foundations Logical thinking and problem solving ability

How to become a good programmer?
1. Look for where you are wrong?
2. Be open to learn
3. Don’t stop at “the code works”
4. Read codes!!!
5. Learn techniques not tools
6. KISS
7. Analyse the problem
8. Work-around don’t work
9. Code doesn’t end with source file
10. Don’t compare with other programmers
Adaptations from
- “8 Ways to Become a Better Coder”
by Esther Schindler
- “10 Effective Ways to Become a Good
Programmer” by Ashish Arya

Role of IDEs in effective programming
● Refactoring
● Source Control
● Reduction of learner’s pain
● Visual debugger
● Auto complete
● Centralization
- Adaptation from “The Importance of the IDE in Software Development”

Version Control Systems
● Manage source code over time
● Track every modifications to the code
● Benefits
○ Change history
○ Branching and merging
○ Traceability Adaptations from
- “What is Version Control” by
Atlassian Bitbucket
Do It Yourself (DIY)
● “Learn Git with Bitbucket Cloud (Interactive tutorial)” by Atlassian Bitbucket

Competitive Programming
● Brings a blend of data structures,
Algorithm Design and Analysis and
Good problem-solving skills
● Competitive programming vs ML
contests
● Contest arenas
○ Top coder, Code chef
○ Project Euler
○ Hacker Rank, Hacker Earth
● ML Contests
○ Kaggle
○ The AI Games
Suggested Reads
● Want to ace technical interviews?
Get started with Competitive
Programming! - Aditya Rohilla
● The 10 most popular coding
challenge websites for 2017 -
Daniel Borowski
● What should every competitive
programmer (Topcoder) know
about Kaggle and ML contests? -
Quora

Python
Introduction to Python language

PYPL Popularity of Programming
Tiobe-index

Why is python so popular?
Notable reads:
● Why is Python so popular despite being so slow? - Quora
● Why is Python slower than the xxx language (wiki.python.org)
● Simple, ease of use, constantly improving
● High level language (still runs on any platform)
● Factors into consideration
○ Might be considered slow due to interpretation - 9/10 it doesn’t matter
○ Presence of Global Interpreter Lock (GIL)

Python interpreter
Ref: Why is Python a dynamic language and also a strongly typed language? (wiki.python.org)
Python is:
● Interpreted language
● Dynamically typed language
● Strongly typed language

Application areas
● Integration and user tasks
● Scientific and Computational Applications
● Prototyping applications
● Web and internet development
● Software development
● Data mining and visualization
● Embedded systems
● Social science
● Machine learning and deep learning
● …. And a lots more….

Python
versions
2.7.x vs 3.x
Detailed read:
● Should I use Python 2 or Python 3 for my development activity? (wiki.python.org)

Python IDLE and Python interpreter
● Basic ways of using Python
○ Python interpreter via
command line
○ Python IDLE
● When using cmd
○ Write on any text editor
○ No separate steps for
compilation
○ Just have to add python to
path
○ Run the script using “python
<script>.py”

Anaconda
● Free and open source distribution
for Python and R
● Conda - environment management
and package management
● Navigator - Virtual environment
manager (GUI)
● Anaconda Cloud - package
management service

Using third party modules
● Third party modules are available in plenty (PyPI)
● Installation is possible via conda and pip
● Pip (2008) succeed easy_install (2004)
● Whl prebuilt versions for windows are available through other sources
● Conda and Pip are the most preferred
Notable reads:
● https://stackoverflow.com/questions/3220404/why-use-pip-over-easy-install

Beginner’s
Programming
Python basics

Variables in Python
● Reserved memory locations to store values
● The interpreter allocates memory and decides what can be stored in the reserved
memory
● The declaration happens automatically when you assign a value to a variable
Multiple assignment
● a = b = c = 1
● a, b, c = 1, 2, "john"
Suggested reads:
● Learn about id() function
● CPython Optimizations (faster-cpython.readthedocs.io)
● Python Variable Assignment Statements and Naming Rules & Conventions
(thehelloworldprogram.com)

Data types
Conversion between data types
● Convert between different data types by using different type conversion functions
like int(), float(), str() etc

L = []
L = [expression,..]
L = [expression for variable
in sequence]
L = list()
L = list(sequence)
Lists
● List of comma-separated values
(items) between square brackets.
● Items in a list need not be of the
same type.
● List indices start at 0, and lists can
be sliced, concatenated and so on.

List operations
● Accessing lists
○ L[start:stop]
● Slicing lists
○ L[start:stop:slice]
● Searching
○ L.index(value)
● Reversing
● Sorting
● Modifying lists
○ L[i] = object
○ L[i:j] = sequence
○ append(item)
○ extend(sequence)
○ insert(index, item)
○ del L[i]

Tuples
● Tuples are sequences, just like lists.
● The differences between tuples and lists are, the tuples cannot be changed unlike
lists and tuples use parentheses, whereas lists use square brackets.
● You cannot update or change the values of tuple elements.
● Tuple operations
○ Length
○ Concatenation
○ Repetition
○ Membership
○ Iteration

Sets
● Sets are lists with no duplicate entries
● Unordered collection of unique elements
● Sets are a powerful tool in Python since they have the ability to calculate
differences and intersections between other sets.
● Set operations
○ Intersection
○ Difference
○ Symmetric_difference
○ Union

Dictionaries
● Each key is separated from its value by a colon (:)
● The items are separated by commas
● The whole thing is enclosed in curly braces. {}
● Keys are unique within a dictionary while values may not be.
● Keys can be strings, tuples or numbers
diy_1_dictionaries.py

Conditionals
if test expression:
body of if
elif test expression:
body of elif
else:
body of else
● Block scope is achieved via Indentation and not via parenthesis
● Elif ladder can be programmed for any level
● Nested if is possible for any level
● There is no switch case in Python

DIY: Input statements
1. Write a program to convert temperatures to celsius from fahrenheit. (c/5 = (f -
32)/9)
a. Get input from user using input() function
b. Enter a prompt message when getting input from user
2. Expand the program to understandable format
3. Find the difference between eval(input()) and input()
4. Print the type of the input entered by the user
5. Validate the user input - input should only take float
diy_2_input_stmts.py

DIY: Conditionals
1. Write a program to check if the number is odd or even
2. Write a program to get the name of the day and print the number of the day in the
week. (For example, if the user enters ‘Sunday’ print ‘first day of the week’)
a. Also handle inputs that are not days of the week and print ‘invalid day’
b. Can you convert the el-if ladder to a dictionary??
3. Write a program that will generate a random playing card e.g. ‘9 Hearts’, ‘Queen
Spades’ when the return key is pressed.
diy_3_conditionals_p1.py, diy_3_conditionals_p2.py, diy_3_conditionals_p3.py

Looping constructs
Break statement
● The break statement is used to immediately leave the body of its loop.
● The next statement to be executed is the first one after the body
Continue statement
● This is a control flow statement that causes the program to immediately skip the
processing of the rest of the body of the loop, for the current iteration.
● But the loop still carries on running for its remaining iterations:
while BOOLEAN_EXPRESSION:
STATEMENTS
for LOOP_VARIABLE in SEQUENCE:
STATEMENTS

DIY: Looping constructs
1. Write a Python program which iterates the integers from 1 to 50. For multiples of
three print "Fizz" instead of the number and for the multiples of five print "Buzz".
For numbers which are multiples of both three and five print "FizzBuzz". Hint:
range() function
2. Define a procedure histogram() that takes a list of integers and prints a histogram
to the screen. For example, histogram([4, 9, 7]) should print the following:
****
*********
*******
diy_4_loops_p1.py, diy_4_loops_p2.py

List comprehension
Syntactic construct that enables lists to be created from other lists using a compact,
mathematical syntax
output_sequence = []
for item1 in seq1:
for item2 in seq2:
...
for itemx in seqx:
if condition:
output_sequence.append(expr)
[expr for item1 in seq1 for item2 in seq2 ... for itemx in
seqx if cond]

List comprehension - Examples
>>> numbers = [1, 2, 3, 4]
>>> [x**2 for x in numbers]
[1, 4, 9, 16]
>>> [x**2 for x in numbers if x**2 > 8]
[9, 16]
>>> [(x, x**2, x**3) for x in numbers]
[(1, 1, 1), (2, 4, 8), (3, 9, 27), (4, 16, 64)]
>>> letters = ['a', 'b', 'c']
>>> [n * letter for n in numbers for letter in letters]
['a', 'b', 'c', 'aa', 'bb', 'cc', 'aaa', 'bbb', 'ccc', 'aaaa', 'bbbb', 'cccc']
>>>

Strings
● Strings are created simply by enclosing characters in quotes.
● Python treats single quotes the same as double quotes.
● Creating strings is as simple as assigning a value to a variable
● String format operator - %s
● r’expression’ and u’expression’
○ r - raw string (used in paths, regex, etc)
○ u - unicode string
diy_5_strings.py
Suggested reads
● https://learn.rmotr.com/python/understanding-unicode-in-python/strings-and-unicode/unicode
-in-python

Regular expressions - A gateway for string
matching
● Sequence of characters that define a search pattern
● Used by string matching algorithms
● Each character in regular expression is either a meta character or a literal character
● The module re provides full support for Perl-like regular expressions in Python
● Match and search functions
diy_6_regex_p1.py, diy_6_regex_p2.py

Mutability of data types
● Mutable data types
○ Mutable objects can be changed after getting created
○ Lists are mutable data types
● Immutable data types
○ Immutable objects cannot be changed after creating
○ Tuples are immutable data types
● Identify the mutability of other data types!!

Functions
● Named sequence of instructions
● Use the new names without having to consider the details of the instructions to
which they refer.
Return statement
● The return statement causes a function to immediately stop executing statements
in the function body
● Send back (or return) the value after the keyword return to the calling statement.
def NAME( LIST OF PARAMETERS ):
STATEMENTS

Properties of functions
● Passing list as parameters
○ Call by reference and call by value - nether - it is call by assignment
● Functions as data
○ Storing functions as list
● Pure functions - Does not produce side effects, only result is in return statement
● Modifiers - A layer of packaging of the original function (Check decorators!!!)
● Recursive functions
● Polymorphism
● Duck typing
diy_7_fns_purefns.py, diy_7_fns_modifiers.py, diy_7_fns_duck_type.py

Recursion
● Recursion is a way of programming or coding a problem, in which a function calls
itself one or more times in its body.
● Usually, it is returning the return value of this function call.
● If a function definition fulfils the condition of recursion, we call this function a
recursive function

DIY: Functions
1. Write a Python program which accepts the radius of a circle from the user and
compute the area.
2. Convert the weekday program as a function based program
3. Create a function that would take two arguments, weight and height and return
BMI (BMI = xKG/(yM*yM))
a. Convert the height as default parameter
b. Convert the second parameter as a variable argument list
i. Get age and height in the second parameter
diy_7_fns_p1.py, diy_7_fns_p3.py

DIY: Functions
4. Create a function that would return the double of a parameter
a. Check polymorphism by passing different data types as a parameter
5. Write a recursive function to find factorial of a number (Try giving a very large
number as input)
6. Create a list of functions and iterate each function with same parameters and
observe the difference
diy_7_fns_p4.py, diy_7_fns_p5.py

Modules and Packages
● A module allows you to logically organize your Python code.
● Simply, a module is a file consisting of Python code.
● A module can define functions, classes and variables.
● A module can also include runnable code.
● Packages are namespaces which contain multiple packages and modules
themselves. They are simply directories
● Importing modules
○ import module1[, module2[,... moduleN]
○ from modname import name1[, name2[, ... nameN]]
○ from modname import *
diy_8_modules.py

DIY: Modules and Packages
● Create a file called greetings.py
● Define a function called hello(name) and print “hello: name”
● Import the module greetings
● Call the function hello passing your name as parameter
● Move this to a folder called greetings (Note that if both greetings module and
package cannot exist together)
● Create another function called bye(name)
● Add an empty file called _init_.py
● Try calling the bye function with your name
diy_8_packages.py, hello.py, greetings (folder)

● Miscellaneous operating system interfaces
● Working with directories and files
● Working with processes
○ Starting a new process
○ Forking a process
○ Running programs in background
● Invoking a daemon process
Suggested read:
● http://effbot.org/librarybook/os.htm
OS Module

● SYS Module
○ System-specific parameters and functions
○ Command line arguments
○ Standard data streams
● CSV Module
○ Read and write tabular data
○ Reader and writer objects to read and write sequences
SYS and CSV Modules
diy_9_csv_module.py

DIY: User input and file handling
1. The given folder contains different types of files
2. Display the available file names to the user (Use listdir in os module)
3. Ask user to enter name of a file (Use input)
4. Provide the extension of the file type (Use os.path.splittext)
5. Provide the size of the file (Use os.path.getsize)
6. Write the filename and size of the file to a csv file (Use csv module)
7. Write the filename and size of the file to a text file
8. Can you try modifying the user input to a command line argument?? (Use sys.argv)
9. Can you find other statistics of a file (os.stat)

Classes
● Classes and objects
○ Classes are like modules
○ Objects are like imports
○ __init__ method
○ Getters and setters
○ Access specifiers
● Inheritance
○ Is-A and has-A relationships
class ClassName:
<statement-1>
.
.
.
<statement-N>
diy_10_classes_p1.py, diy_10_classes_p2.py, diy_10_classes_p3.py, diy_10_classes_p4.py

DIY: Classes
● Define a class person with three attributes of different data types
● Create a object to the class
● Inherit the person class to employee class
● Add attribute salary to employee class
● Create object for employee class
● Try to retrieve the attributes of person class using employee class object (Check if
upcasting and downcasting are possible?)

Scopes and Namespaces
Scopes
The scope of a definition is the part of the program over
which the definition holds
Namespaces
Roughly speaking, namespaces are just containers for
mapping names to objects.
LEGB Rule
Suggested Reads
● http://www.python-course.eu/python3_namespaces.php
● http://www.network-theory.co.uk/docs/pytut/PythonScopesandNameSpaces.html
● http://python-textbok.readthedocs.io/en/1.0/Variables_and_Scope.html
diy_11_scopes_p1.py,
diy_11_scopes_p2.py,
diy_11_scopes_p3.py

Error and exception handling
● An exception is an error that
happens during execution of a
program.
● When that error occurs, Python
generate an exception that can be
handled, which avoids your
program to crash.
try:
You do your operations here;
......................
except ExceptionI:
If there is ExceptionI, then
execute this block.
except ExceptionII:
If there is ExceptionII, then
execute this block.
......................
else:
If there is no exception then
execute this block.
raise [Exception [, args [,
traceback]]]
diy_12_exceptions.py

DIY: Catch the exceptions
● Create a function to compute the sqrt of a number
● Use try… except block to catch TypeError
● Raise error to display a custom message when the number is 0
diy_12_exceptions_p1.py

Iterators and Generators
● Iterators
○ Returns a python iterator - one value at a time
○ Two methods are available: __iter__() and __next__()
● Generators
○ Create iterators using yield
○ Generators are used for laze evaluations
○ Reusable generators are created using Object Oriented Generators
○ Generator expressions are used for high performance optimizations for list
comprehensions

Thinking like a programmer
“There are no standards for computer
programmers and no group to certify them”

Python debugger
● Debugging using command prompt
○ python -m pdb <filename.py>
● Debugging options
○ p - print
○ n - next
○ l - list
○ c - restart the execution
○ s - step
○ r - return

DIY: Spot the errors and correct them
diy_13_debugging_p1.py, diy_13_debugging_p2.py, diy_13_debugging_p3.py
Reference:
1. http://tjelvarolsson.com/blog/five-exercises-to-master-the-python-debugger/
2. https://docs.python.org/3/library/pdb.html
3. http://ericholscher.com/blog/2008/aug/30/using-pdb-python-debugger-django-d
ebugging-series-/
4. https://pythonconquerstheuniverse.wordpress.com/2009/09/10/debugging-in-py
thon/

Loggers
● Logging is important for system developing, debugging and running.
● When a program crashes, if there is no logging record, you have little chance to
understand what happened.
Reference:
● https://fangpenlin.com/posts/2012/08/26/good-logging-practice-in-python/
diy_14_loggers.py

Python practices
● Programming practices
○ PEP8 Style guide (https://www.python.org/dev/peps/pep-0008/)
○ BOBP Guide for Python (https://gist.github.com/sloria/7001839)
● Zen of python - software principles that influence the design of Python Language
○ import this
● Structure of python projects
○ Filesystem structure of a Python project
(http://as.ynchrono.us/2007/12/filesystem-structure-of-python-project_21.
html)
○ Python Dev Workflow (https://docs.pipenv.org/)
● Scaffolding
○ PyScaffold (https://pypi.org/project/PyScaffold/)
○ Scaffold for Python (https://github.com/Aaronontheweb/scaffold-py)

Python In and Out
Advanced Python Usage

Python for Scientific Computing
NumPy
● Fundamental package for scientific computing in Python
● Supports large, multi-dimensional arrays and matrices
● Holds several high level mathematical functions for matrix operations
Scipy
● Module for optimization, linear algebra, integration, signal and image processing
● Works on numpy arrays
● Key algorithms and function cores for Python scientific computing capabilities

Python for Scientific Computing
Matplotlib
● Plotting library for Python
● API for embedding plots into applications using GUI Toolkits
● 2D plotting in publication quality fig with different formats and interactive
environments
Pandas
● Data manipulation and analysis library
● Provides data structures and operations for numeric tables and time series
● Highly optimized for performance (most of the critical code is written in Cython or
C)

Machine Learning in Python
Scikit-learn
● Machine learning library for Python (data mining and data analysis)
● Classification, Regression and clustering algorithms
● Built on numpy, scipy and matplotlib
Scikit-image
● Image processing library for Python
● Covers all basic algorithms for segmentation, geometric transforms, color space
manipulations, feature detection, filtering, etc.
● Interoperates with NumPy and SciPy

Image Processing in Python
Pillow
● Python Imaging Library
● Support for multiple file formats with powerful image processing capabilities
● Ideal for batch processing and conversion of different file formats
OpenCV-Python
● Python bindings to solve computer vision problems
● Infrastructure to build computer vision applications and to accelerate the use of
machine perception in commercial products

Interfaces with Python
GUIs with TkInter
● Python binding to Tk GUI Toolkit
● Tkinter calls are translated to Tcl commands and are used by the Tcl interpreter
available in the Python interpreter
● Positions of widgets within the containers are done using packers
● Application variables and Widgets are connected using the subclasses of Variable
class
● Bind methods are used to watch for events and trigger callback functions
● Alternates for TkInter
○ wxPython, PyQt, Pygame, Pyglet, PyGTK

Interfaces with Python
Web interfaces with Flask
● Microframework for Python
● Supports extensions that can add application features.
● Flask does not have database abstraction layer, form validation by default
● Easy to setup and works well for smaller applications
● Has built in development server and debugger
● Alternatives for Flask
○ Django, Pyjs, Tornado

Books
● Learn Python - The Hard Way - EBook
○ https://learnpythonthehardway.org/book/
● A Byte of Python - EBook
○ https://python.swaroopch.com/
● Think Python: How to Think Like a Computer Scientist - EBook (PDF/HTML)
○ http://greenteapress.com/thinkpython/html/index.html
● Intro CS - Harvey Mudd College - Lecture Series (This covers more than
programming)
○ https://www.cs.hmc.edu/csforall/

Video Lectures
● Learn Python - Codecademy
○ https://www.codecademy.com/learn/learn-python
● Google for Education - Python
○ https://developers.google.com/edu/python/
● Intro to Python for Data Science - Video lectures
○ https://www.datacamp.com/courses/intro-to-python-for-data-science
● MIT 6.00SC Introduction to Computer Science and Programming (26 Lectures)
○ https://www.youtube.com/playlist?list=PLB2BE3D6CA77BB8F7

Online Resources
● The Python Tutorial
○ https://docs.python.org/3/tutorial/index.html
● Python Tricks - Newsletter - short python code snippets
○ https://realpython.com/python-tricks/
● Learn X in Y minutes - Where X=Python
○ https://learnxinyminutes.com/docs/python/
● List of Python Frameworks, Libraries, Softwares and Resources
○ https://github.com/vinta/awesome-python

Python Challenge
● http://www.pythonchallenge.com/
● Python based online programming riddle
● All levels have to be solved using Python Scripts
● Helps you explore the language in an entertaining way
● Form groups and try to crack the challenge

That’s all folks :) :)
Have a wonderful career

Blueprints: Introduction to Python programming

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