Python Keywords, Literals, Operators & Comments

Keywords, Literals, Operators & Comments

Python Keywords

Python Keywords are special reserved words which convey a special meaning to the compiler/interpreter. Each keyword have a special meaning and a specific operation. These keywords can't be used as variable. Following is the List of Python Keywords.

True	False	None	and	as
asset	def	class	continue	break
else	finally	elif	del	except
global	for	if	from	import
raise	try	or	return	pass
nonlocal	in	not	is	lambda

Python Literals

Literals can be defined as a data that is given in a variable or constant.

Python support the following literals:

I. String literals:

String literals can be formed by enclosing a text in the quotes. We can use both single as well as double quotes for a String.

Eg:

"Aman" , '12345'

Types of Strings:

There are two types of Strings supported in Python:

a).Single line String- Strings that are terminated within a single line are known as Single line Strings.

Eg:

text1 = ‘hello’

b).Multi line String- A piece of text that is spread along multiple lines is known as Multiple line String.

There are two ways to create Multiline Strings:

1). Adding black slash at the end of each line.

Eg:

>>> text1='hello\ 

user' 

>>> text1 

'hellouser' 

2).Using triple quotation marks:-

Eg:

>>> str2='''''welcome

to

SSSIT''' 

>>> print str2 

welcome 

to 

SSSIT 

II.Numeric literals:

Numeric Literals are immutable. Numeric literals can belong to following four different numerical types.

Int(signed integers)        

Long(long integers)       

float(floating point)        

Complex(complex)

III. Boolean literals:

A Boolean literal can have any of the two values: True or False.

IV. Special literals.

Python contains one special literal i.e., None.

None is used to specify to that field that is not created. It is also used for end of lists in Python.

Eg:

>>> val1=10 

>>> val2=None 

>>> val1 

10 

>>> val2 

>>> print val2 

None

V.Literal Collections.

Collections such as tuples, lists and Dictionary are used in Python.

List:

• List contain items of different data types. Lists are mutable i.e., modifiable.
• The values stored in List are separated by commas(,) and enclosed within a square brackets([]). We can store different type of data in a List.
• Value stored in a List can be retrieved using the slice operator([] and [:]).
• The plus sign (+) is the list concatenation and asterisk(*) is the repetition operator.

Eg:

>>> list=['aman',678,20.4,'saurav'] 

>>> list1=[456,'rahul'] 

>>> list 

['aman', 678, 20.4, 'saurav'] 

>>> list[1:3] 

[678, 20.4] 

>>> list+list1 

['aman', 678, 20.4, 'saurav', 456, 'rahul'] 

>>> list1*2 

[456, 'rahul', 456, 'rahul']  

Python Operators

The operator can be defined as a symbol which is responsible for a particular operation between two operands. Operators are the pillars of a program on which the logic is built in a particular programming language. Python provides a variety of operators described as follows.

• Arithmetic operators

• Comparison operators

• Assignment Operators

• Logical Operators

• Bitwise Operators

• Membership Operators

• Identity Operators

Arithmetic operators:

Arithmetic operators are used to perform arithmetic operations between two operands. It includes +(addition), - (subtraction), *(multiplication), /(divide), %(reminder), //(floor division), and exponent (**).

Comparison Operators:

Comparison operators are used to comparing the value of the two operands and returns boolean true or false accordingly. It includes ==, !=, <=, >=, <>, >, <.

Python Assignment Operators:

The assignment operators are used to assign the value of the right expression to the left operand. It includes =, +=, -=, *=, %=, **=, //=.

Bitwise operators:

The bitwise operators perform bit by bit operation on the values of the two operands. It includes &(binary and), |(binary or), ^(binary xor), ~(negation), <<(left shift), >>(right shift).

Logical operators:

The logical operators are used primarily in the expression evaluation to make a decision. It includes not, and, or.

Membership operators:

Python membership operators are used to check the membership of value inside a data structure. If the value is present in the data structure, then the resulting value is true otherwise it returns false. It includes in and not in.

Identity operators:

is and is not are identity operators

Operator Precedence:

The precedence of the operators is important to find out since it enables us to know which operator should be evaluated first. The precedence table of the operators in python is given below.

Operator	Description
**	The exponent operator is given priority over all the others used in the expression.
~ + -	The negation, unary plus and minus.
* / % //	The multiplication, divide, modules, reminder, and floor division.
+ -	Binary plus and minus
>> <<	Left shift and right shift
&	Binary and.
^ |	Binary xor and or
<= < > >=	Comparison operators (less then, less then equal to, greater then, greater then equal to).
<> == !=	Equality operators.
= %= /= //= -= += *= **=	Assignment operators
is is not	Identity operators
in not in	Membership operators
not or and	Logical operators

Python Comments

Python supports two types of comments:

1) Single Line Comments

In case user wants to specify a single line comment, then comment must start with ?#?

Eg:

# This is single line comment.

2) Multiline comments

Multi lined comment can be given inside triple quotes.

Eg:

''''' This 

    Is 

    Multipline comment'''