Python Programming - Variables, Objects and Classes

PYTHON
PROGRAMMIN
G
BY
MRS. V. JAYAVANI
ASSISTANT PROFESSOR
DEPARTMENT OF COMPUTER SCIENCE

WHAT IS PYTHON?
 Python is a popular high-level programming language used in various applications.
 Python is an easy language to learn because of its simple syntax.
 Python can be used for simple tasks such as plotting or for more complex tasks like machine
learning.

VARIABLES, OBJECTS, AND CLASSES
 A variable is a reference to a value stored in a computer’s memory.
 Variables can be sorted into a variety of categories (or data types) such as numbers (int/float
etc), boolean values (true/false), and sequences (strings, lists etc).
 An object is a collection of data from a computer’s memory that can be manipulated.
 All variables are objects although some objects can be defined by data referred to
by multiple variables.
 Methods are the functions used to act on/alter an object’s data. they describe what
your object can “do.”

VARIABLES, OBJECTS, AND CLASSES (CONT.)
 A class is a collection of objects who
share the same set of variables/methods.
 The definition of the class provides
a blueprint for all the objects within
it (instances).
 Instances may share the same
variables (color, size, shape, etc.),
but they do not share the same
values for each variable
(blue/red/pink, small/large,
square/circular etc.)
Instance #1
Color: Pink
Name: Polo
Instance #2
Color: Red
Name: Mini
Instance #3
Color: Blue
Name: Beetle

BASIC SYNTAX RULES
 The name of your variable (myint etc.) is placed on the left of the “=“ operator.
 Most variable names are in camel case where the first word begins with a lowercase letter and any
subsequent words are capitalized.
 Variable names may also appear in snake case where all words are lowercase, with underscores between
words.
 The assignment operator (“=“) sets the variable name equal to the memory location where your value is found.
 The value of your variable (“hello, world”) is placed on the right of the “=“ operator.
 The type of this value does not need to be stated but its format must abide by a given object type (as shown).
myString = “Hello, World” myInt = 7
myFloat = 7.0
myList = [7, 8, 9] myBoolean = true

BASIC SYNTAX RULES (CONT.)
 FUNCTION SYNTAX
 def...: indicates that you are defining a new function.
 function() refers to the name of your function. by convention, this name is typically lowercase and represents
a verb/action.
 A,B refers to parameters (values or variables) that can be used within the statements of your function’s
definition (......). if your function has no parameters, an empty parenthetical () is used.
 The return statement is an optional statement that will return a value for your function to your original call.
def function(a, b):
......
return a + b

BASIC SYNTAX RULES (CONT.)
 CALLING A FUNCTION
 Call the function by referring to its name (function()) and by placing any necessary
arguments (1, 2) within the parenthesis separated by commas. myvalue = function(1, 2)
 If you wish, you can set your function call equal to a variable (myvalue). the value
returned by the function will be assigned to your variable name.
myValue = function(1, 2)

COMMON DATA TYPES AND OPERATORS
 A data type is a means of classifying a value and determining what operations can be
performed on it. all objects have a data type.
 Operators are symbols used carry out specific functions/computations.
 https://www.youtube.com/watch?v=v5mr5jnkczi

INPUT/OUTPUT
 Input functions (input()) allow users of a program to place values into programming code.
 The parameter for an input function is called a prompt. this is a string (this can be indicated by “” or ‘’)
such as “enter a number: “
 The user’s response to the prompt will be returned to the input statement call as a string. to use this
value as any other data type, it must be converted with another function (int()).
 Print functions (print()) allow programs to output strings to users on a given interface.
 The parameter of this function is of any type. all types will automatically be converted to strings.
xString = input(“Enter a number: “)
x = int(xString)
y=x+2
print(y)

IF-ELSE STATEMENTS
 If-else statements allow programmers to adapt the function of their code
based on a given condition.
 If a given condition (i.e. x % 2 == 0) is true, then the statements following
the if statement (if) will be executed. if the condition is false, the statements
following the else statement (else) will be executed.
 The condition is tested using the boolean operators == (is equal to), !
= (is not equal to), and (used to test multiple conditions), and or
(used to test if at least one condition is true).
 Additionally, else-if statements (elif) can be used to provide unique
coding statements for multiple conditions.
xString = input(“Enter a number: “)
x = int(xString)
if x % 2 == 0:
print(“This is an even number”)
elif x == 0:
print(“This number equals 0”)
else:
print(“This is an odd number”)

FOR LOOPS
 For loops perform the same task (iterate) for the number of
times specified by an iterable (something that can be evaluated
repeatedly such as a list, string, or range).
 For defines the for loop
 X is the variable defining the number of times the statements
within the loop (print(myint)) are executed.
 The range(start, stop, step) function is often used to define x.
 The starting value is defined by start, the final value is
defined by stop – 1, and the magnitude at which x
changes between loops is defined by step.
 In is a boolean operator that returns true if the given value (x) is
found within a given list, string, range etc.
myString = input(“Enter a number: “)
myInt = int(myString)
for x in range(0, 5, 1): print(myInt)

WHILE LOOPS
● While loops are statements that iterate so long as a given
boolean condition is met.
○ x (the variable determining whether or not the
condition is met) is defined and manipulated outside
of the header of the while loop (while)
○ The condition (x < 5) is a statement containing a
boolean variable.
○ Break is a statement used to exit the current for/while
loop.
○ Continue is a statement used to reject all statements in
the current for/while loop iteration and return to the
beginning of the loop.
myString = input(“Enter a number: “)
myInt = int(myString)
x = 0
while x < 5:
print(myInt)
x= x +1

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