ogn g Pythonwith Python - ERNETpkalra/csl101/python1.pdf · • t s e used to ex plain the ppg ro...

Introduction to ProgrammingIntroduction to Programmingwith Pythonwith Pythonwith Pythonwith Python

1515K.K. Biswas, IIT Delhi

PYTHON IS A PROGRAMMINGPYTHON IS A PROGRAMMINGLANGUAGE

K.K. Biswas, IIT Delhi 16

What is a program?What is a program?

• Sequence of instructions to perform some computationq p p• Example: A shirt costs Rs 250. How many shirts can one buy

given Rs Rs 2350? What will be the balance amount left?• Solution worked on paper:• Shirts = 2360/250 = 9 (and some money left)• Cost of shirts 250 x 9 2250• Cost of shirts = 250 x 9 = 2250• Balance = Amount �– Cost of shirts = 100


Skeleton of a programSkeleton of a program

• Amount = 2360Amount 2360• Shirts = 2360/250 = 9• Cost of shirts = 250 x 9 = 2250Cost of shirts = 250 x 9 = 2250• Balance = Amount �– Cost of shirts = 100


a python programa python program

• a = 2360a = 2360• c = 250

/• x = a / c• t = c * x• b = a �– t• print bprint b


a better python programa better python program

• amount = 2360amount = 2360• cost_ shirt = 250

hi / hi• shirts = amount / cost_ shirt• total_cost = cost_ shirt * shirts• balance = amount �– total_cost• print balanceprint balance


variables in pythonvariables in python

• amount = 2360• amount ( Variable)• 2360 ( value)• Variable names– amt, b, A, amount5, amt66– amount_given, num_boys, numgirls– 23amount (WRONG !) can not start with a number

high value (WRONG !) can not have a space– high value (WRONG !) can not have a space– also key words not allowed (See page 11 of Think Python )


Data TypesData Types

• 236 (int)( )• 5000 (int)• 7.62 (floating point)• 0.025 (floating point)• 611285.3 (floating point)

• �‘hello, world !�’ (string)• �‘grade is fine�’ (string)• grade is fine (string)• �‘my marks are�’ (string)


Assignment StatementsAssignment Statements

• The syntax of an assignment statement is thaty g• a variable is always on the left hand side of an equal sign,• and the right hand side it could be

– a value– another variable– an arithmetic expressionan arithmetic expression

• variable = expression• amount = 2360• (this means, amount is assigned the value 2360)• x = amount• (this means, x is assigned the value held by amount)



• shirts = amount / cost shirt/ _• amount / cost_ shirt is an expression• (this means, variable shirts is assigned the value of the above

expression)• total_cost = cost_ shirt * shirts• cost shirt * shirts is another expression• cost_ shirt * shirts is another expression



• age = age + 1g g• (this means age is assigned the value

of the expression age + 1)• You can write• variable = variable• x = age

• BUT you cannot write• BUT you cannot write• expression = variable• age + 1 = age ( WRONG !)age 1 age ( WRONG !)


statements in pythonstatements in python

• profit = sale price �– cost priceprofit sale_price cost_price• print profit

• Statements– assignment statements– print statements


Operators and OperandsOperators and Operands

• y = b + ky• ( b and k are called operands)• z = y �– a• w = y * z• shirts = amount / cost_one

/• shirts = 2360 / 250(Note: INTEGER DIVISION, result is always an integer)= 9 and not 9 44= 9 and not 9.44

• p = m ** 3 ( m raised to power 3) EXPONENTIATION


Operators and OperandsOperators and Operands

• How to get the remainder of a division operation?g p• use the mod operator %• a%b evaluates to the remainder of a divided by b.•• 13%5 = 3• 19%6 = 1• 14%7 = 0• 19%200 = 19• 19%200 = 19• 23/6 = 3• 23%6 = 523%6 5


Order of OperationsOrder of Operations

• The PEMDAS ruleThe PEMDAS rule• 6 + 8 * (3 + 7) �– 2 % 9 ** 4P th i hi h t d• Parenthesis are highest order

• Exponentiation( )• Multiplication, Division, (Mod operators)

• Addition and Subtraction• Operators with same precedence evaluated left toright


Order of OperationsOrder of Operations

• To handle the arithmetic expressions properly, the computerp p p y, puses the following order of precedence while doing left toright evaluations.

•( )* / %/ %

+ �–

• Operators with same precedence evaluated left toright


solving a mathematical expressionsolving a mathematical expression

7 / 3 * 1.2 + 3 / 2

7 / 3 * 1 2 + 3 / 27 / 3 * 1.2 + 3 / 2

2 * 1.2 + 3 / 2

2.4 + 3 / 2

2.4 + 1

3.433K.K. Biswas, IIT Delhi

solving a mathematical expressionsolving a mathematical expression

• 2 + 8 * (12 �– 5 ) % 10• 2 + 8 * 7 % 10• 2 + 56 % 10• 2 + 6


Handling int and float valuesHandling int and float values

• a = 9• b = 4• d = 10.0• e = 4• c = a/b• f = d + e• g = d/b• r = a * 1 0 / b• r = a * 1.0 / b• c = 2 f = 14.0• g = 2.5 r = 2.25g 2.5 r 2.25

K.K. Biswas, IIT Delhi 35

solving arithmetic expressionssolving arithmetic expressions

• Try to evaluate the following expressionsTry to evaluate the following expressions• 4 + 6 * 2• 4 * 6 + 24 6 + 2• 49 / 6 + 1• 8 / 2 * 6• 8 / 2 6• 8 * 2 / 6• 8 73 % 9 / 3• 8 �– 73 % 9 / 3


string operationsstring operations

• x = �‘alpha�’x alpha• y = �‘beta�’• print x + yprint x + y• alphabeta• print y * 3• print y 3• betabetabeta


The �“Comment�” statementThe Comment statement

• comment statements are used to explain the program steps.p p g pBasic idea is to help the reader understand the code.

• Example: Suppose a student gets 43 marks out of 75 and weti t f k bt i dare computing percentage of marks obtained.

• # this calculates percentage of marks• percent = ( marks * 100) / 75 0percent = ( marks 100) / 75.0• # marks is int value but percent is floating point

• percent = ( marks * 100) / 75.0 # percent is float value• vel = 6 # velocity is in metres/sec


sample programsample program

• Find the volume of a sphere with radius 5. AnFind the volume of a sphere with radius 5. Anapproximate value would do.

• r = 5• pi = 3.14• volume = (4.0/3) *PI *r * r* rvolume (4.0/3) PI r r r• print volume



• A student gets 92, 72, 83, and 65 in Maths, English, Physicsg , , , , g , yand Chemistry. Add 5 marks to science subjects and find theaverage marks obtained by him.

th 92• math = 92• eng = 72• phy = 83phy = 83• chem = 65• phy = phy + 5p y p y• chem = chem +5• average = ( math + eng + phy + chem)/ 5.0• print average



• Write a program which uses a person�’s age to print number ofp g p g pyears left for retirement (a person retires at 65).

• age = 45• print �‘ you have �‘, 65 �– age , �‘years until retirement.�’

• You can ask the age from the user as well• You can ask the age from the user as well• age = input("How old are you? ")• print ‘your age is ‘, ageprint your age is , age• print ‘ you have ‘, 65 – age , ‘years until retirement.’


Class exerciseClass exercise

• A students camp has got 3 divisions of girls and 5 divisions ofp g gboys. Write a program which asks the user to input number ofboys and girls in each division.It h ld i t• It should print

• number of girls,• number of boys andnumber of boys and• total number of students.


ExerciseExercise• Exercise:Write a Python program that prompts the user fory p g p p

his/her amount of money, then reports how many jean pantsthe person can afford, and how much more money he/she willneed to afford an additional jean pant (cost of jean pant =need to afford an additional jean pant. (cost of jean pant =750)

• Write a program which converts 13 hours and 32 minutes intoseconds.


DebuggingDebugging

• Removing �“bugs�” (errors) from the programg g ( ) p g• Principal = 34000• interest = principal * rate * time

• to r = 1/ 2b/ *• r = 1.0 / 2 * b

• temp 1 = 67• temp 1 = 67• height = 0• width = area / heightwidth area / height


ogn g Pythonwith Python - ERNETpkalra/csl101/python1.pdf · • t s e used to ex plain the ppg ro...

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