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Fundamentals of PythonProgramming

Introduction to python programming• High level, interpreted language• Object-oriented• General purpose• Web development (like: Django and Bottle),• Scientific and mathematical computing (Orange, SciPy, NumPy)• Desktop graphical user Interfaces (Pygame, Panda3D).

• Other features of python includes the following:• Simple language which is easier to learn• Free and open source• Portability• Extensible and embeddable• Standard large library

• Created by Guido van Rossum in 1991• Why the name Python?• Not after a dangerous snake.• Rossum was fan of a comedy series from late seventies.• The name "Python" was adopted from the same series "Monty Python'sFlying Circus".

Reasons to Choose Python as First Language• Simple Elegant Syntax• Not overly strict• Expressiveness of the language• Great Community and Support

Installation of Python in Windows• Go to Download Python page on the official site(https://www.python.org/downloads/) and click Download Python3.6.5 (You may see different version name)• When the download is completed, double-click the file and follow theinstructions to install it.• When Python is installed, a program called IDLE is also installed alongwith it. It provides graphical user interface to work with Python.

• Open IDLE, Write the following code below and press enter.print("Hello, World!")• To create a file in IDLE, go to File > New Window (Shortcut: Ctrl+N).• Write Python code and save (Shortcut: Ctrl+S) with .py file extensionlike: hello.py or your-first-program.pyprint("Hello, World!")• Go to Run > Run module (Shortcut: F5) and you can see the output.

Few Important Things to Remember• To represent a statement in Python, newline (enter) is used.• Use of semicolon at the end of the statement is optional (unlikelanguages like C/C++)• In fact, it's recommended to omit semicolon at the end of thestatement in Python• Instead of curly braces { }, indentations are used to represent a block

Python Keywords• Keywords are the reserved words(can not be used as a identifier) inPython• Are case sensitive

Python Identifiers• Name given to entities like class, functions, variables etc. in Python• Rules for writing identifiers• Can be a combination of letters in lowercase (a to z) or uppercase (A to Z) ordigits (0 to 9) or an underscore (_)• myClass, var_1 and print_this_to_screen, all are valid examples• Cannot start with a digit• 1variable is invalid, but variable1 is perfectly fine• Keywords cannot be used as identifiers• Cannot use special symbols like !, @, #, $, % etc. in our identifier• Can be of any length.

Things to care about• Python is a case-sensitive language.• Variable and variable are not the same.• Multiple words can be separated using an underscore,this_is_a_long_variable• Can also use camel-case style of writing, i.e., capitalize every firstletter of the word except the initial word without any spaces• camelCaseExample

Python Statement• Instructions that a Python interpreter can execute are calledstatements.• Two types• Single line statement:• For example, a = 1 is an assignment statement• Multiline statement:• In Python, end of a statement is marked by a newline character.• So, how to make multiline statement?

• Technique1:• make a statement extend over multiple lines with the line continuationcharacter ().• For example:a = 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9

• Technique2:• make a statement extend over multiple lines with the parentheses ( )• For example:a = (1 + 2 + 3 +4 + 5 + 6 +7 + 8 + 9)

• Technique3:• make a statement extend over multiple lines with the brackets [ ] and braces {}.• For example:colors = ['red','blue','green']

• We could also put multiple statements in a single line usingsemicolons, as followsa = 1; b = 2; c = 3

Python Indentation• Most of the programming languages like C, C++, Java use braces { } todefine a block of code• Python uses indentation• A code block (body of a function, loop etc.) starts with indentationand ends with the first un-indented line

Error due to incorrect indentation

Python Comments• To make the code much more readable.• Python Interpreter ignores comment.• Two types of comment is possible in python:• Single line comment and• Multi-line comment

Single line comment• In Python, we use the hash (#) symbol to start writing a comment.• It extends up to the newline character

Multi-line comments• Two way:• By using # sign at the beginning of each line#This is a long comment#and it extends#to multiple lines• By using either ‘ ‘ ‘ or “ “ “ (most common)"""This is also aperfect example ofmulti-line comments"""

Python Variable• a variable is a named location used to store data in the memory.• Alternatively, variables are container that hold data which can bechanged later throughout programming

Declaring Variables• In Python, variables do not need declaration to reserve memoryspace.• The "variable declaration" or "variable initialization" happensautomatically when we assign a value to a variable.• We use the assignment operator = to assign the value to a variable.

Assigning same value to the multiple variable

Assigning multiple values to multiple variables

Constants• Value that cannot be altered by the program during normalexecution.• In Python, constants are usually declared and assigned on a module• And then imported to the file

Rules and Naming convention for variablesand constants• Create a name that makes sense. Suppose, vowel makes more sensethan v.• Use camelCase notation to declare a variable• For example: myName, myAge, myAddress• Use capital letters where possible to declare a constant• For example: PI,G,MASS etc.

• Never use special symbols like !, @, #, $, %, etc.• Don't start name with a digit.• Constants are put into Python modules• Constant and variable names should have combination of letters inlowercase (a to z) or uppercase (A to Z) or digits (0 to 9) or anunderscore (_).• For example: snake_case, MACRO_CASE, camelCase, CapWords

Literals• Literal is a raw data given in a variable or constant. In Python, thereare various types of literals they are as follows:• Numeric literals• String literals• Boolean literals• Special literals

Data Types• In python data types are classes and variables are instance (object) ofthese classes• Different types of data types in python are:• Python numbers• Python lists• Python tuples• Python strings• Python sets• Python dictionary

Python List• Ordered sequence of items• Can contain heterogeneous data• Syntax:• Items separated by commas are enclosed within brackets [ ]• Example: a= [1,2.2,'python']

Extracting elements from the list

• Note: Lists are mutable, meaning, value of elements of a list can bealtered.

Python Tuple• Same as list but immutable.• Used to write-protect the data• Syntax:• Items separated by commas are enclosed within brackets ( )• Example:• t = (5,'program', 1+3j)

Python Strings• use single quotes or double quotes to represent strings.• Multi-line strings can be denoted using triple quotes, ''' or """.• Example:s = "This is a string"s = '''a multilinestring’’’• Strings are also immutable.

Python Set• Unordered collection of unique items• defined by values separated by comma inside braces { }

• Set have unique values. They eliminate duplicates.• Example:

• Since, set are unordered collection, indexing has no meaning.• Hence the slicing operator [] does not work.• Example:

Python Dictionary• An unordered collection of key-value pairs.• Must know the key to retrieve the value.• Are defined within braces {} with each item being a pair in the formkey: value• Key and value can be of any type

Conversion between data types• Conversion can be done by using different types of type conversionfunctions like:• int(),• float(),• str() etc.

convert one sequence to another

• To convert to dictionary, each element must be a pair:

Python Type Conversion and Type Casting• The process of converting the value of one data type (integer, string,float, etc.) to another data type is type conversion• Python has two types of type conversion.• Implicit Type Conversion• Explicit Type Conversion

• Type Conversion is the conversion of object from one data type toanother data type• Implicit Type Conversion is automatically performed by the Pythoninterpreter• Python avoids the loss of data in Implicit Type Conversion• Explicit Type Conversion is also called Type Casting, the data types ofobject are converted using predefined function by user• In Type Casting loss of data may occur as we enforce the object tospecific data type

Implicit Type Conversion• Automatically converts one data type to another data type• Always converts smaller data type to larger data type to avoid the lossof data

Problem in implicit type conversion

Explicit Type Conversion• Users convert the data type of an object to required data type.• Predefined functions like int(), float(), str(), etc. are to perform explicittype conversion• Is also called typecasting because the user casts (change) the datatype of the objects.• Syntax :• (required_datatype)(expression)• Int(b)

Python Input, Output and Import• Widely used functions for standard input and output operations are:• print() and• input()

Python Output Using print() function

Output formatting• Can be done by using the str.format() method• Is visible to any string object• Here the curly braces {} are used as placeholders. We can specify theorder in which it is printed by using numbers (tuple index).

• We can even use keyword arguments to format the string

• We can even format strings like the old printf() style used in C• We use the % operator to accomplish this

Input() function• input() function to take the input from the user.• The syntax for input() is :• input([prompt])• where prompt is the string we wish to display on the screen.• It is optional

• Entered value 10 is a string, not a number.• To convert this into a number we can use int() or float() functions• This same operation can be performed using the eval(). It canevaluate expressions, provided the input is a string.

Python Import• When our program grows bigger, it is a good idea to break it intodifferent modules.• A module is a file containing Python definitions and statements.• Python modules have a filename and end with the extension .py• Definitions inside a module can be imported to another module orthe interactive interpreter in Python• We use the import keyword to do this

• import some specific attributes and functions only, using the fromkeyword.

Python Operators• Operators are special symbols in Python that carry out arithmetic orlogical computation.• The value that the operator operates on is called the operand.• For example:>>> 2+35• Here, + is the operator that performs addition.• 2 and 3 are the operands and 5 is the output of the operation.

Bitwise operators• Bitwise operators act on operands as if they were string of binarydigits. It operates bit by bit, hence the name.• For example, 2 is 10 in binary and 7 is 111.• In the table below: Let x = 10 (0000 1010 in binary) and y = 4 (00000100 in binary)

Assignment operators• Assignment operators are used in Python to assign values tovariables.• a = 5 is a simple assignment operator that assigns the value 5 on theright to the variable a on the left.• There are various compound operators in Python like a += 5 that addsto the variable and later assigns the same.• It is equivalent to a = a + 5.

Special operators• identity operator• membership operator

Identity operators• is and is not are the identity operators in Python.• They are used to check if two values (or variables) are located on thesame part of the memory.• Two variables that are equal does not imply that they are identical.

Membership operators• in and not in are the membership operators in Python• They are used to test whether a value or variable is found in asequence (string, list, tuple, set and dictionary).• In a dictionary we can only test for presence of key, not the value

Python Namespace and Scope• Name (also called identifier) is simply a name given to objects.• Everything in Python is an object• Name is a way to access the underlying object.• For example:• when we do the assignment a = 2, here 2 is an object stored in memory and ais the name we associate it with• We can get the address (in RAM) of some object through the built-in function,id()

A name could refer to any type of object

Functions are objects too, so a name canrefer to them as well

What is a Namespace in Python?• namespace is a collection of names.• Help to eliminate naming collision/naming conflict

• A namespace containing all the built-in names is created when westart the Python interpreter and exists as long we don't exit• Each module creates its own global namespace• Modules can have various user defined functions and classes.• A local namespace is created when a function is called, which has allthe names defined in it.• Similar, is the case with class

Python Variable Scope• All namespaces may not be accessible from every part of the program• Scope is the portion of the program from where a namespace can beaccessed directly without any prefix

• At any given moment, there are at least three nested scopes.• Scope of the current function which has local names• Scope of the module which has global names• Outermost scope which has built-in names• When a reference is made inside a function, the name is searched inthe local namespace, then in the global namespace and finally in thebuilt-in namespace.• If there is a function inside another function, a new scope is nestedinside the local scope.

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