Variables in Python

Variables in Python are reserved memory locations to store values. This means that when a variable is created, a space is reserved in memory.

The interpreter allocates memory based on the data type of a variable. Therefore, by assigning different data types to variables, you can store integers, decimals or characters in these variables.

Assigning Values to Variables

Unlike other high level languages, variables in Python do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable. The equal sign (=) is used to assign values to variables.

The operand to the left of the = operator is the name of the variable and the operand to the right of the = operator is the value stored in the variable. For example −

Multiple Assignment

Python allows you to assign a single value to several variables simultaneously. For example

a = b = c = 1
Here, first an integer object is created with the value 1 stored in it, and all three variables are assigned to the same memory location. You can also assign multiple objects to multiple variables. For example −

a,b,c = 1,2,”string”
Here, two integer objects with values 1 and 2 are assigned to variables a and b respectively, and one string object with the value “string” is assigned to the variable c.

Standard Data Types

Python has five standard data types −

• Numbers
• String
• List
• Tuple
• Dictionary

Python Numbers

Number data types are used in Python to store numeric values. Number objects are created when values are assigned to them. For example −

var1 = 1
var2 = 10
You can also delete the reference to a number object by using the del statement. The syntax of the del statement is −

del var1[,var2[,var3[….,varN]]]]
You can delete a single object or multiple objects by using the del statement. For example −

del var1
del var2, var3
Python supports four different numerical types −

• int (signed integers)
• long (long integers, they can also be represented in octal and hexadecimal)
• float (floating point real values)
• complex (complex numbers)

Examples

Here are some examples of numbers −

Integer – 10

Long – 51924361L (Python displays long integers with an uppercase L)

Float – 0.0

Complex – 9+5j

Python Strings

A group of characters enclosed within quotations are called strings. These quotations can either be single or double.

Slicing: Subsets of strings can be taken using the slice operator ([ ] and [:] ) with indexes starting at 0 in the beginning of the string and working their way from -1 at the end.

Concatenation: The plus (+) sign is the string concatenation operator and the asterisk (*) is the repetition operator. For example −

Python Lists

A list contains items separated by commas and enclosed within square brackets ([]). Lists are similar to arrays in C to some extent. Major difference between them is that all the items belonging to a list can be of different data type. Whereas an array contains items of same datatype.

Slicing and concatenation can be used in lists as they are used in strings.

For example −

Python Tuples

A tuple is another sequential data type that is similar to the list with values separated by commas. Tuples are enclosed within parentheses() unlike lists[].

Values in a list can be changed at any time, whereas values inside a tuple cannot be updated.

For example −

Python Dictionary

A Dictionary in Python is similar to a list, but enclosed in curly braces ({ }). Values are stored in a Dictionary in the format of a key:Value Pair.

For example −

Data Type Conversion

There are several built-in functions to perform conversion from one data type to another. These functions return a new object representing the converted value.

Sr.No.	Function & Description
1	int(x [,base]) Converts x to an integer. base specifies the base if x is a string.
2	long(x [,base] ) Converts x to a long integer. base specifies the base if x is a string.
3	float(x) Converts x to a floating-point number.
4	complex(real [,imag]) Creates a complex number.
5	str(x) Converts object x to a string representation.
6	repr(x) Converts object x to an expression string.
7	eval(str) Evaluates a string and returns an object.
8	tuple(s) Converts s to a tuple.
9	list(s) Converts s to a list.
10	set(s) Converts s to a set.
11	dict(d) Creates a dictionary. d must be a sequence of (key,value) tuples.
12	frozenset(s) Converts s to a frozen set.
13	chr(x) Converts an integer to a character.
14	unichr(x) Converts an integer to a Unicode character.
15	ord(x) Converts a single character to its integer value.
16	hex(x) Converts an integer to a hexadecimal string.
17	oct(x) Converts an integer to an octal string.