XII (IP)

BASICS OF PYTHON

Program :- A program is a set of instructions that perform a specific tasks.

Python :-

• It is created by Guido Van Rossum in the late 1980's at National research Institute for Mathematics and Computer Science in the Netherlands.
• Easy to learn and use.
• It is very powerful and expressive high level language.
• It is an open source, cross-platform, dynamic and interpreted high level language.
• It is derived from many other languages such as ABC, Modula-3, C, C++, Algol-68, SmallTalk, and unix shell.
• It's interpreter and extensive standard library available at "http://www.python.org/"

Features of Python :-

• It is easy to use and learn.
• It has a broad library.
• It is a free and open source.
• It is portable and interpreted.
• It is based on object-oriented concepts.
• It is extensible.
• It is dynamically typed.

Modes of writing python code :- Basically we can write the python code in two modes

1. Interactive Mode.
2. Script mode.

Interactive mode :- 

• Interactive mode is a command line shell which gives immediate results for each statement.
• Interactive mode makes it easy to test code snippets before incorporating them into a larger program.
• The ">>>" is called Python Prompt which indicates that we are in interactive mode i.e. it is ready to take input from the user.

Script Mode :- 

• We use the script mode to write a set of statements in Python.
• In this mode, a set of statements is stored in a file with .py extension.

IDLE :- It is a graphical "Integrated Development Environment" for Python. It contains a Python shell program that lets us type instruction into the compiler.

Different IDE where python code can be executed

• Jupyter
• Anaconda
• Spyder
• Gitbash with VSode
• Pycharm
• PyScripter IDE
• Jython (Java)
• IronPython (.NET)

Python as Interpreted Language :-

• Python is interpreted language , i.e. it is processed at runtime by the interpreter and it need not to compile the program before executing it.
• The interpreter checks through the code for errors and interprets the instructions into machine readable "bytecode"
• This is similar to PERL and PHP.

Byte Code :- 

• Python code is translated into intermediate code called byte code, which has to be executed by a virtual machine known as Python Virtual Machine (PVM).
• A bytecode is a byte-long instruction that python interpreter generates and executes.
• Execution of a python program means execution of the byte code on the Python Virtual Machine (PVM).

Applications of Python

• Web development
• Machine Learning
• Deep learning
• Rapid Prototyping
• Scripting
• Game development
• System administration
• GUI Programming

Python Character Set :- Character sets are the building blocks of any programming language. In Python basic program elements are identifier or variable, array, etc as given below.
Letters :- Uppercase Letters (A-Z)
                Lowercase Letters (a-z)
Digits :- 0.........9
Special Characters :- / * + \ " < > # ( ) = | { % - ; } [] / ^ - :' ? & _ '. 
                                (blank)
White spaces :- Blank spaces, Tab, carriage return, newline, form feed
Other Characters :- It can process all ASCII and UNICODE character as part of data or literals.

Token :-  A token is the smallest unit of the program. The various tokens of python are shown below :

• It is also known as Lexical unit.
• In a passage of text, individual words and punctuation marks are called token or lexical units
• Python has following tokens: -

1. Keywords
2. Identifiers
3. Literals
4. Operators
5. Punctuation.

Keywords in Python :- 

• Python keywords are special reserved words.
• Convey a special meaning to the compiler / interpreter.
• Each keyword has a special meaning and a specific operation.
• It is not used as variable, method or class names.
• There are 33 keywords in Python and are case sensitive.
• Example : True, False, None, and, as , asset, def, class etc.

Literals in Python :- In Python literals mean data items that have a constant value. Following are the types of literals :-

1. String Literals
2. Numeric Literals
3. Boolean Literals
4. Special Literals

** These are the data which are stored in a variable.

String Literals :- It is a sequence of characters surrounded by quotes ( single, double or triple)
Example : - >>> name1 = "John"
                  >>> name2 = 'James'

Numeric Literals :-

Int	long	float	complex
+ve & -ve numbers (integers) with no fractional part Example :- 100, 24	unlimited integer size followed by upper or lower case L Example :- 2345446L	Real numbers with both integers and fractional part Example:- 213.32	In the form of a + bj. 'a' form the real part & 'bj' forms the imaginary parts Example :- 3+4j

Boolean Literals :- It can have two values "True" or "False" , where condition of two value is required.

Special Literals :- Python has one special Literal : None, It is used to specify that field which is not created.

Example:-   >>> val2 = None ("There is nothing here")

Identifier :- Identifiers are names given to program elements such as variables, arrays and functions. Basically, identifiers are the sequences of alphabet or digits.

Variable :- 

• A variable is declared to hold some spaces in the memory.
• The data stored in a variable can then be modified, stored or displayed whenever needed.
• Example :- sum = 0   ("here sum is variable with a default value of 0 and when a user enters data, the variable changes to the data entered by users.

Escape Sequence :- 

• It is a special character followed by a backslash (\).
• This makes the normal character to be interpreted with a new meaning.
• Example :- 'n' becomes new line character after adding (\), i.e. '\n'.
• \\ - Backslash (\)
• \' - single quote (')
• \r - carriage return
• \t - Horizontal tab
• \000 - character set with octal value

Comment :- 

• A line of text which starts with a hash (#) symbol is known as comment in Python
• It will be skipped by the interpreter during the program execution. 
• A comment can be written as a new line or with the statement or expression line.
• Example : - >>> # This is a new line comment at interactive mode                              >>> x = 20  # This is comment with expression line

Delimiters :- Delimiters can be defined as a sequence of one or more characters that is used to specify the boundary between separate independent regions in plain text or other data streams.
Example :- Delimiter example is comma(,). for some method like split(), default limiter is whitespace.

Data :-  

• The data we manipulate in Python consists of objects and names.
• Each object in Python has three key attributes: a type,   a value & an id.

Data Types :- 

•  Data type of a variable indicate the kind of value that a variable can store.
• The data types indicates the attributes of the variable, such as range of values that can be stored and the operators that can be used to manipulate the variable,.
• Python has a rich collection of data types.