Python Fundamentals

 

Python Fundamentals

• In order to provide an input, process it and to receive output, we need to write a program. 
• Program, is a group of instructions which controls processing. 
• In other words, base for processing is ‘the Program’. 
• In this chapter we will come to know about various element of processing like – character set, token, expressions, statements, input.

Python Character Set

Character Set-is a group of letters or signs which are specific to a language. 

• Character set includes letter, sign, number, symbol. 
• Letters: A-Z, a-z 
• Digits: 0-9  
• Special Symbols: _, +, -, *, /, (, ), {, } . . . Etc. 
• White Spaces: blank space, tab, carriage return, newline, formfeed etc. 
• Other characters: Python can process all characters of ASCII and UNICODE.

Tokens

Token- is the smallest unit of any programming language.

           It is also known as  Lexical Unit. 

Types of token are :-

1. Keywords 
2. Identifiers (Names) 
3. Literals 
4. Operators 
5. Punctuators

Keywords

Keywords are those words which provides a special meaning to interpreter. 

• These are reserved for specific functioning. 
• These can not be used as identifiers, variable name or any other purpose. 
• Available keywords in Python are :-

Identifiers 

These are building blocks of a program and are used to give names to different parts/blocks of a program like - variable, objects, classes, functions. 

• An identifier may be a combination of letters and numbers. 
• An identifier must begin with an alphabet or an underscore( _ ). Subsequent letters may be numbers(0-9). 
• Python is case sensitive. Uppercase characters are distinct from lowercase characters (P and p are different for interpreter). 
• Length of an Identifier is unlimited. 
• Keywords can not be used as an identifier. 
• Space and special symbols are not permitted in an identifier name except an underscore( _ ) sign. 
• Some valid identifiers are – – Myfile, Date9_7_17, Z2T0Z9, _DS, _CHK FILE13. 
• Some invald identifiers are – – DATA-REC, 29COLOR, break, My.File.

Literals / Values 

Literals are often called Constant Values. 

Python permits following types of literals - 

• String literals :- “Pankaj” 
• Numeric literals :– 10, 13.5, 3+5i 
• Boolean literals :– True or False 
• Special Literal None :– Literal collections.

String Literals 

String Literal is a sequence of characters that can be a combination of letters, numbers and special symbols, enclosed in quotation marks, single, double or triple(“ “ or ‘ ‘ or “’ ‘”). 

In python, string is of 2 types- 

• Single line string :- 
• Text = “Hello World” or Text = ‘Hello World’ 
• Multi line string :-
• Text = ‘hello\

                         world’ 
           or 

• Text = ‘’’hello  word ‘’’ 

Numeric Literals 

Numeric values can be of three types - 

1. int (signed integers)
• Decimal Integer Literals :– 10, 17, 210 etc. 
• Octal Integer Literals :- 0o17, 0o217 etc. 
• Hexadecimal Integer Literals :– 0x14, 0x2A4, 0xABD etc. 

    2. float ( floating point real value) 

• Fractional Form :– 2.0, 17.5 -13.5, -.00015 etc. 
• Exponent Form : -1.7E+8, .25E-4 etc. 

    3. Complex (complex numbers) : 

• 3+5i etc. 

Boolean Literals 

It can contain either of only two values – True or False 

•  A= True 
•  B= False 

 

Special Literals 

 None, which means nothing (no value). 

•  X = None

Operators 

An Operator is a symbol that trigger some action when applied to identifier (s)/ operand (s) . 

Therefore, an operator requires operand (s) to compute upon. 

example : c = a + b 

• Here, a, b, c are operands and operators are = and + which are performing differently.

Types of Operators 

 Python supports following types of operators - 

• Unary Operator 
• Unary plus (+) 
• Unary Minus (-) 
• Bitwise complement (~) 
• Logical Negation (not) 
• Binary Operator 
• Arithmetic operator (+, -, *, /, %, **, //) 
• Relational Operator(<, >, <=, >=, ==, != ) 
• Logical Operator (and, or) 
• Assigment Operator (=, /=, +=, -=, *=, %=, **=, //=) 
• Bitwise Operator (& bitwise and, ^ bitwise xor, | bitwise or) 
• Shift operator (<< shift left, >> shift right) 
• Identity Operator (is, is not) 
• Membership Operator (in, not in) 

Punctuators 

In Python, punctuators are used to construct the program and to make balance between instructions and statements.

• Punctuators have their own syntactic and semantic significance. 
• Python has following Punctuators - ‘ , ” , #, \, (, ), [, ], {, }, @. ,, :, .. `, =

A Python Program Structure