Python Variables and Data type
Variables are nothing but reserved memory locations to store values. This means that when you create a variable you reserve some space in memory.
Based on the data type of a variable, the interpreter allocates memory and decides what can be stored in the reserved memory. Therefore, by assigning different data types to variables, you can store integers, decimals or characters in these variables.
Python variables do not need explicit declaration to reserve memory space. The declaration happens automatically when you assign a value to a variable.
Assigning value to python 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 −
#!/usr/bin/python
countofpen = 100 # An integer assignment
priceofpen = 12.50 # A floating point
nameofcustomer = “Satya” # A string
print countofpen
print priceofpen
print nameofcustomer
Python also allows you to assign a single value to several variables simultaneously.
For example:-
a = b = c = 1
Here, an integer object is created with the value 1, and all three variables are assigned to the same memory location.
You can also assign multiple objects to multiple variables.
a, b, c = 1, 2, “Satya”
Here, two integer objects with values 1 and 2 are assigned to variables a and b respectively, and one string object with the value “Satya” is assigned to the variable c.
Python Standard Data Types
Python has various standard data types that are used to define the operations possible on them and the storage method for each of them.
Python has five standard data types −
1. Python Numbers
Number data types store numeric values. Number objects are created when you assign a value to them. For Example:-
test1 = 1
test2 = 2
test3=4
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
- Python allows you to use a lowercase L with long, but it is recommended that you use only an uppercase L to avoid confusion with the number 1. Python displays long integers with an uppercase L.
- A complex number consists of an ordered pair of real floating-point numbers denoted by x + yj, where x and y are the real numbers and j is the imaginary unit.
2. Python Strings
- Strings in Python are identified as a contiguous set of characters represented in the quotation marks.
- Python allows for either pairs of single or double quotes.
- 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.
- The plus (+) sign is the string concatenation operator and the asterisk (*) is the repetition operator
Example:-
#!/usr/bin/python
str = ‘Hello World!’
print str # Prints complete string
print str[0] # Prints first character of the string
print str[2:5] # Prints characters starting from 3rd to 5th
print str[2:] # Prints string starting from 3rd character
print str * 2 # Prints string two times
print str + “Satya” # Prints concatenated string
Output:
Hello World!
H
llo
llo World!
Hello World!Hello World!
Hello World!Satya
3. Python Lists
- Lists are the most versatile of Python’s compound data types.
- A list contains items separated by commas and enclosed within square brackets ([]).
- To some extent, python lists are similar to arrays in C. One difference between them is that all the items belonging to a list can be of different data type.
- The values stored in a list can be accessed using the slice operator ([ ] and [:]) with indexes starting at 0 in the beginning of the list and working their way to end -1.
- The plus (+) sign is the list concatenation operator, and the asterisk (*) is the repetition operator.
Example:
#!/usr/bin/python
list = [ ‘abcd’, 198 , 2.23, ‘john’, 70.2 ]
tinylist = [123, ‘john’]
print list # Prints complete list
print list[0] # Prints first element of the list
print list[1:3] # Prints elements starting from 2nd till 3rd
print list[2:] # Prints elements starting from 3rd element
print tinylist * 2 # Prints list two times
print list + tinylist # Prints concatenated lists
Output:
[‘abcd’, 198, 2.23, ‘john’, 70.200000000000003]
abcd
[198, 2.23]
[2.23, ‘john’, 70.200000000000003]
[123, ‘john’, 123, ‘john’]
[‘abcd’, 198, 2.23, ‘john’, 70.200000000000003, 123, ‘john’]
4. Python Tuples
- A tuple is another sequence data type that is similar to the list.
- A tuple consists of a number of values separated by commas.
- Unlike lists, however, tuples are enclosed within parentheses.
- The main differences between lists and tuples are: Lists are enclosed in brackets ( [ ] ) and their elements and size can be changed, while tuples are enclosed in parentheses ( ( ) ) and cannot be updated.
- Tuples can be thought of as read-only lists.
Example:
#!/usr/bin/python
tuple = ( ‘abcd’, 198 , 2.23, ‘john’, 70.2 )
tinytuple = (123, ‘john’)
print tuple # Prints complete list
print tuple[0] # Prints first element of the list
print tuple[1:3] # Prints elements starting from 2nd till 3rd
print tuple[2:] # Prints elements starting from 3rd element
print tinytuple * 2 # Prints list two times
print tuple + tinytuple # Prints concatenated lists
Output:
(‘abcd’, 198, 2.23, ‘john’, 70.200000000000003)
abcd
(18, 2.23)
(2.23, ‘john’, 70.200000000000003)
(123, ‘john’, 123, ‘john’)
(‘abcd’, 198, 2.23, ‘john’, 70.200000000000003, 123, ‘john’)
Invalid tuple code
#!/usr/bin/python
tuple = ( ‘abcd’, 786 , 2.23, ‘john’, 70.2 )
list = [ ‘abcd’, 786 , 2.23, ‘john’, 70.2 ]
tuple[2] = 1000 # Invalid syntax with tuple
list[2] = 1000 # Valid syntax with list
5. Python Dictionary
- Python’s dictionaries are kind of hash table type.
- They work like associative arrays or hashes found in Perl and consist of key-value pairs.
- A dictionary key can be almost any Python type, but are usually numbers or strings. Values, on the other hand, can be any arbitrary Python object.
- Dictionaries are enclosed by curly braces ({ }) and values can be assigned and accessed using square braces ([]).
Example:
#!/usr/bin/python
dict = {}
dict[‘one’] = “This is one”
dict[2] = “This is two”
tinydict = {‘name’: ‘john’,’code’:6734, ‘dept’: ‘sales’}
print dict[‘one’] # Prints value for ‘one’ key
print dict[2] # Prints value for 2 key
print tinydict # Prints complete dictionary
print tinydict.keys() # Prints all the keys
print tinydict.values() # Prints all the values
Output:
This is one
This is two
{‘dept’: ‘sales’, ‘code’: 6734, ‘name’: ‘john’}
[‘dept’, ‘code’, ‘name’]
[‘sales’, 6734, ‘john’]
