Python
Programming Notes and Practical Programs BCA 3rd Semester CSJM
University Kanpur
Python Variables with examples
Variables are used to store data, they take memory
space based on the type of value we assigning to them. Creating variables in
Python is simple, you just have write the variable name on the left side of =
and the value on the right side, as shown below.
Num = 20 #num is of type int
str = "Ankit" #str is of type string
Variable name – Identifiers
Variable name is known as identifier. There are few
rules that you have to follow while naming the variables in Python.
1. The name of the variable must always start with either a letter or an
underscore (_). For example: _str, str,
num, _num are all valid name for the variables.
2. The name of the variable cannot start with a number. For example: 9num is not a valid variable name.
3. The name of the variable cannot have special characters such as %, $, #
etc, they can only have alphanumeric characters and underscore (A to Z, a to z,
0-9 or _).
4. Variable name is case sensitive in Python which means num and NUM are two different
variables in python.
Python Variable Example
num = 100
str = "BeginnersBook"
print(num)
print(str)
Output:
100
BeginnersBook
Python multiple assignment
We can assign multiple variables in a single
statement like this in Python.
x = y = z = 99
print(x)
print(y)
print(z)
Output:
99
99
99
Another example of multiple assignment
a, b, c = 5, 6, 7
print(a)
print(b)
print(c)
Output:
5
6
7
Plus and concatenation operation on the variables
x = 10
y = 20
print(x + y)
p = "Hello"
q = "World"
print(p + " " + q)
Output:
30
Hello World
However if you try to use the + operator with
variable x and p then you will get the following error.
unsupported operand type(s) for +: 'int' and 'str'
Data Types
A data type defines the type of data, for example 123 is an integer data while “hello” is a String type of data. The
data types in Python are divided in two categories:
1. Immutable data types – Values
cannot be changed.
2. Mutable data types – Values can
be changed
Immutable
data types in Python are:
1. Numbers
2. String
3. Tuple
Mutable
data types in Python are:
1. List
2. Dictionaries
3. Sets
1. Numeric Data Type in Python
Integer – In Python 3,
there is no upper bound on the integer number which means we can have the value
as large as our system memory allows.
# Integer number
num = 100
print(num)
print("Data Type of variable num is", type(num))
Output:
100
Data Type
of variable num is <class ‘int’>
Long – Long data type is deprecated in Python 3 because there is no need for it, since the integer has no upper limit, there is no
point in having a data type that allows larger upper limit than integers.
Float – Values with decimal points are the float
values, there is no need to specify the data type in Python. It is
automatically inferred based on the value we are assigning to a variable. For
example here fnum is a float data type.
# float number
fnum = 34.45
print(fnum)
print("Data Type of variable fnum is", type(fnum))
Output:
34.45
Data Type of variable fnum
is <class ‘float’>
Complex Number –
Numbers with real and imaginary parts are known as complex numbers. Unlike
other programming language such as Java, Python is able to identify these
complex numbers with the values. In the following example when we print the
type of the variable cnum, it prints as complex number.
# complex number
cnum = 3 + 4j
print(cnum)
print("Data Type of variable cnum is", type(cnum))
Output:
(3+4j)
Data Type of variable cnum is
<class ‘complex’>
Binary, Octal and Hexadecimal numbers
In Python we can print decimal equivalent of binary,
octal and hexadecimal numbers using the prefixes.
0b(zero + ‘b’) and 0B(zero + ‘B’) – Binary Number
0o(zero + ‘o’) and 0O(zero + ‘O’) – Octal Number
0x(zero + ‘x’) and 0X(zero + ‘X’) – Hexadecimal Number
# integer equivalent of binary number 101
num = 0b101
print(num)
# integer equivalent of Octal number 32
num2 = 0o32
print(num2)
# integer equivalent of Hexadecimal number FF
num3 = 0xFF
print(num3)
Output:
5
26
255
2. Python Data Type – String
String is a sequence of characters in Python. The
data type of String in Python is called “str”.
Strings in Python are either enclosed with single
quotes or double quotes. In the following example we have demonstrated two
strings one with the double quotes and other string s2 with the single quotes.
# Python program to print strings and type
s = "This is a String"
s2 = 'This is also a String'
# displaying string s and its type
print(s)
print(type(s))
# displaying string s2 and its type
print(s2)
print(type(s2))
Output:
This is a String
<class ‘str’>
This is also a String
<class ‘str’>
3. Python Data Type – Tuple
Tuple is immutable data type in Python which means
it cannot be changed. It is an ordered collection of elements enclosed in round
brackets and separated by commas.
# tuple of integers
t1 = (1, 2, 3, 4, 5)
# prints entire tuple
print(t1)
# tuple of strings
t2 = ("hi", "hello", "bye")
# loop through tuple elements
for s in t2:
print (s)
# tuple of mixed type elements
t3 = (2, "Lucy", 45, "Steve")
'''Print a specific elementindexes start with zero'''
print(t3[2])
Output:
(1, 2, 3, 4, 5)
Hi
Hello
Bye
45
4. Python Data Type – List
List is similar to tuple, it is also an ordered
collection of elements, however list is a mutable data type which means it can
be changed unlike tuple which is an immutable data type.
A list is enclosed with square brackets and elements
are separated by commas.
# list of integers
lis1 = [1, 2, 3, 4, 5]
# prints entire list
print(lis1)
# list of strings
lis2 = ["Apple", "Orange", "Banana"]
# loop through list elements
for x in lis2:
print (x)
# List of mixed type elements
lis3 = [20, "csa ", 15, "csaankit"]
'''Print a specific element in listindexes start with zero'''
print("Element at index 3 is:",lis3[3])
Output:
[1, 2, 3, 4, 5]
Apple
Orange
Banana
Element at index 3 is: csaankit
5. Python Data Type – Dictionary
Dictionary is a collection of key and value pairs. A
dictionary doesn’t allow duplicate keys but the values can be duplicate. It is
an ordered, indexed and mutable collection of elements.
The keys in a dictionary doesn’t necessarily to be a
single data type, as you can see in the following example that we have 1
integer key and two string keys.
# Dictionary example
dict = {1:"Ankit","lastname":"Shukla", "age":28}
# prints the value where key value is 1
print(dict[1])
# prints the value where key value is "lastname"
print(dict["lastname"])
# prints the value where key value is "age"
print(dict["age"])
Output:
Ankit
Shukla
28
6. Python Data Type – Set
A set is an unordered and unindexed collection of
items. This means when we print the elements of a set they will appear in the
random order and we cannot access the elements of set based on indexes because
it is unindexed.
Elements of set are separated by commas and enclosed in curly braces. Lets take an example to understand the set.
# Set Example
myset = {"hi", 2, "bye", "Hello World"}
# loop through set
for a in myset:
print(a)
# checking whether 2 exists in myset
print(2 in myset)
# adding new element
myset.add(99)
print(myset)
Output:
hi
2
bye
Hello World
True
{'hi', 2, 99, 'Hello World', 'bye'}