CHAPTER 1
PYTHON
• Interactive, interpreted, and object-oriented programming
language.
• Simple syntax
• Developed by Guido Van Rossum in 1991 at the National
Research Institute for Mathematics and Computer Science in the Netherlands.
• Name was inspired by: Monty Python’s Flying Circus
1.1
PYTHON PROGRAMMING ENVIRONMENT
• Available on a wide variety of platforms including Windows,
Linux and Mac OS X.
• Official Website: python.org
• IDLE stands for Integrated Development and Learning
Environment. Python IDLE com- prises Python Shell and Python Editor. Python
Shell Python Editor
1.2
Display on screen
>>>print('hello world')
hello world
1.3
Names (Variables) and Assignment Statements
• Variables provide a means to name values so that they can
be used and manipulated later.
• Assignment Statement: Statement that assigns value to a
variable.
>>> english = 57
>>>print(english)
Python associates the name
(variable) english with value 57 i.e. the name (variable) english is assigned
the value 57, or that the name (variable) english refers to value 57. Values
are also called objects.
1.3.1
Rules for creating a name (variable)
• Must begin with a letter or _ (underscore character)
• May contain any number of letters, digits, or underscore
characters. No other character apart from these is allowed.
1.3.2
Shorthand Notation
In [3]: a = 6
a = a + 5
print(a)
a = 6
a += 5
print(a)
11
11
2
1.3.3
Multiple Assignments
• Used to enhance the readability of the program.
>>>msg, day, time = 'Meeting', 'Mon', '9'
totalMarks = count = 0
1.4
Arithmetic Operators
>>>print("18 + 5 =", 18 + 5) #Addition
print("18
- 5 =", 18 - 5) #Subtraction
print("18
* 5 =", 18 * 5) #Multiplication
print("27
/ 5 =", 27 / 5) #Division
print("27
// 5 =", 27 // 5) #Integer Division
print("27
% 5 =", 27 % 5) #Modulus
print("2
** 3 =", 2 ** 3) #Exponentiation
print("-2
** 3 =", -2 ** 3) #Exponentiation
18 + 5 = 23
18 - 5 = 13
18 * 5 = 90
27 / 5 = 5.4
27 // 5 = 5
27 % 5 = 2
2 ** 3 = 8
-2 ** 3 = -8
>>>print("'how'
+ ' are' + ' you?':", 'how' + ' are' + ' you?')
print("'hello' * 5 :", 'hello' * 5)
'how' + ' are' + ' you?': how are you? 'hello' * 5 :
hellohellohellohellohello
Precedence
of Arithmetic Operators
1.5
Relational Operators
• Used for comparing two expressions and yield True or
False.
• The arithmetic operators have higher precedence than the
relational operators.
>>> print("23 < 25 :", 23 < 25)
#less than
print("23
> 25 :", 23 > 25) #greater than
print("23 <= 23 :", 23 <= 23)
#less than or equal to
print("23
- 2.5 >= 5 * 4 :", 23 - 2.5 >= 5 * 4) #greater than or equal to
print("23
== 25 :", 23 == 25) #equal to
print("23
!= 25 :", 23 != 25) #not equal to
• When the relational operators are applied to strings,
strings are compared left to right, character by character, based on their
ASCII codes, also called ASCII values.
>>>print("'hello'
< 'Hello' :", 'hello' < 'Hello')
>>>print("'hi'
> 'hello' :", 'hi' > 'hello')
'hello' < 'Hello' : False 'hi' > 'hello' : True’
1.6
Logical Operators
• The logical operators not, and, and or are applied to
logical operands True and False, also called Boolean values, and yield either
True or False.
• As compared to relational and arithmetic operators,
logical operators have the least precedence level.
>>>print("not
True < 25 :", not True) #not operator
>>>print("10
< 25 and 5 > 6 :", 10 < 25 and 5 > 6) #and operator
>>>
print("10 < 25 or 5 > 6 :", 10 < 25 or 5 > 6) #or operator
Precedence
of Logical Operators
Python
Keywords
• Reserved words that are already defined by the Python for
specific uses.
>>>import keyword
print(keyword.kwlist)
[’False’,
’None’, ’True’, ’and’, ’as’, ’assert’, ’break’, ’class’,’continue’, ’def’,
’del’, ’elif’, ’else’, ’except’, ’finally’, ’for’, ’from’, ’global’, ’if’,
’import’, ’in’, ’is’, ’lambda’,’nonlocal’, ’not’, ’or’, ’pass’, ’raise’,
’return’, ’try’, ’while’, ’with’, ’yield’]
