Python Tutorial : Part 3 : Python Datatype

What is Datatype in Python:

Each variable stored in memory has a datatype. Datatypes are actually classes and if you create any variable of a specific datatype, it is an object. Python’s standard datatypes can be grouped into mainly four different classes:

1. Numeric 
2. Sequences
3. Sets
4. Mapping

1.Numeric :
Numeric type includes:

a)  Integer (int): In python, value of an integer can be of unlimited length ( it only depends on the available memory )
b) Long (long): Long integers of unlimited length. But exists only in python 2.x.
c) Float (float): Floating point numbers. Integers and floating point numbers are separated by a decimal point. The maximum no. of places after the decimal for a float is 15 in python.
d) Complex numbers (complex): Complex numbers are represented as ( x + yj ) where x is the real part and y is the imaginary part.

Integer, long, float and complex all are immutable types.

We can use type() function to check which class a variable belongs to.

count1 = 15
print(“count1 type ", type(count1))

count2 = 15.5
print(“count2 type ", type(count2))

count3 = 15 + 6j
print(“count3 type ", type(count3))
Run the above program and you can find the datatype for each variable.

2. Sequences : 

Sequences type includes:

a) Python String (str): String is actually a sequence of 8-bit characters ( in python 2.x ) or a sequence of Unicode characters ( in Python 3.x ). Strings are immutable i.e. we cannot change any character of a String. To represent a String in python, single quote or double quote is used. For multiline strings, a triple quote is used. To print a particular character inside a String, use stringName[position]. Similarly, to print characters in a range, use stringName[firstPosition,lastPosition + 1]

Try to run the following program and check the results:

str1 = 'This is a String'
print str1

str2 = "This is also a String"
print str2

str3 = ''' This is a multiline
String '''
print str3

str4 = """ This is also a multiline
String """
print str4

print("Printing the first character of str1 "+str1[0])
print("Printing the first word of str1 "+str1[0:4])

b) Python list:  
Lists are ordered sequence of variables. A list is mutable, i.e. you can alter any item of a list. Also, list can contain items of different types. To declare a list bracket [] is used. If you want to print or alter a variable inside a list, you can use listname[variablePosition].
Check the following example:

myList = [1,"one",1.0]
print myList

print ("first element of the list is "+str(myList[0]))

myList[0] = "2"

print ("first element is changed")

print ("now , first element is "+myList[0])
At first element was 1. We have changed it to “2”.

c) Python Tuple: 
Python tuple is same as list, the only difference is that it is immutable. To represent tuple in python, we use parentheses ( ). Let’s try with the above example for tuple:

myList = (1,"one",1.0)
print myList

print ("first element of the list is "+str(myList[0]))

myList[0] = "2"

print ("first element is changed")

print ("now , first element is "+myList[0])
It will throw an error on myList[0] = “2” line as we cannot change any values in tuple.

3) Python Sets:

Sets type includes:
a) Set: Set is an unordered collection of unique objects. Each item is separated by a comma inside braces {}.
We can also pass a list to the set function to create a new set.
Check the below example:

mySet1 = set("python")
print mySet1

myList = (1,"one","two")
mySet2 = set(myList)
print mySet2

mySet3 = set([1,1,1,1,1,1])
print mySet3

Output will be like below : 

set(['h', 'o', 'n', 'p', 't', 'y'])
set([1, 'two', 'one'])
You can see that mySet3 contains only one “1” as all values of a set should be unique.
We can perform set operations like add, remove, intersection, union etc on sets.

b) Frozen Sets:
Frozen set is similar as set but they are immutable.  You cannot add any new data to frozen set.

myList = [1,2,3,4]

myFrozenSet = frozenset(myList)
print ("Frozen set "+str(myFrozenSet))

4. Python Mapping:

Mapping type includes:

Python Dictionary:
Python Dictionary is a collection of key-value pairs. Dictionary is an unordered collection. To get any value from dictionary, we must know the key. Dictionaries are defined within braces {}. Each element or key-value pairs can be of any type.

Check the example below :
myDictionary = {"key1":'value1',"key2":2}

print ("Element for key key2 "+str(myDictionary["key2"]))
It will print 2 as value for key “key2” is 2. 


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