CH-3 FEATURES OF PYTHON, data types token

Python Character Set Is a set of valid characters that python can recognize. A character represent letters, digits or any symbol. Python support UNICODE encoding standard. Following are the Python character set  Letter s  Digits : A-Z, a-z : 0-9  Special symbols :space +-*/()~`!@#$%^ & [{ ]};:‟”,<.>/?  White spaces : Blank space, Enter, Tab  Other character : python can process all ASCII and UNICODE as a part of data or literal

TOKENS In a passage of text, individual words and punctuation marks are called tokens or lexical units or lexical elements. The smallest individual unit in a program is known as Tokens. Python has following tokens:  Keywords  Identifiers(Name)  Literals  Operators  Punctuators

KEYWORDS VINOD KUMAR VERMA, PGT(CS), KV OEF KANPUR & SACHIN BHARDWAJ, PGT(CS), KV NO.1 TEZPUR Keywords are the reserved words and have special meaning for python interpreter. Every keyword is assigned specific work and it can be used only for that purpose. A partial list of keywords in Python is

IDENTIFIERS Are the namesgiven to differentparts of program like variables, objects, classes, functions etc. Identifier forming rules of Python are :  Is an arbitrarily long sequence of letters and digits  The first character must be letter or underscore  Upper and lower case are different  The digits 0-9 are allowed except for first character  It must not be a keyword  No special characters are allowed other than underscore is allowed.  Space not allowed

GradePay GRADEPA Y File_12_2018 _ismarried JAMES007 _to_updat e The following are some valid identifiers The following are some invalid identifiers

Literals / Values  Literals are data items that have a fixed value. Python supports several kinds of literals: 🞑 String Literal 🞑 Numeric Literals 🞑 Boolean Literals 🞑 Special Literals – None 🞑 Literal Collections

String Literals  It is a collection of character(s) enclosed in a double or single quotes  Examples of String literals 🞑 “Python” 🞑 “Mogambo” 🞑 „123456‟ 🞑 „Hello How are your‟ 🞑 „$‟, „4‟,”@@”  In Python both single character or multiple characters enclosed in quotes such as “kv”, „kv‟,‟*‟,”+” are treated as same

Non-Graphic (Escape) characters  They are the special characters which cannot be type directly from keyboard like backspace, tabs, enter etc. When the characters are typed they perform some action. These are represented by escape characters. Escape characters are always begins from backslash() character .

List of Escape characters Escape Sequence What it does Escape Sequence What it does Backslash r Carriage return ‟ Single quotes t Horizontal tab ” Double quotes uxxxx Hexadecim al value(16 bit) a ASCII bell Uxxxx Hexadecim al value(32 bit) b Back Space v vertical tab n New line ooo Octal value

String type in Python  Python allows you to have two string types: 🞑 Single Line Strings  The string we create using single or double quotes are normally single-line string i.e. they must terminate in one line.  For e.g if you type as  Name="KV and press enter  Python we show you an error “EOL while scanning string literal”  The reason is quite clear, Python by default creates single-line string with both single quotes and it must terminate in the same line by quotes

String type in Python  Multiline String 🞑 Some times we need to store some text across multiple lines. For that Python offers multiline string. 🞑 T o store multiline string Python provides two ways: (a) By adding a backslash at the end of normal Single / Double quoted string. For e.g. >>> Name="1/6 Mall Road Kanpur" >>> Name '1/6 Mall RoadKanpur' >>>

String type in Python  Multiline String (b) By typing text in triple quotation marks for e.g. >>> Address="""1/7 Preet Vihar New Delhi India""" >>> print(Address) 1/7 Preet Vihar New Delhi India >>> Address '1/7 Preet Vihar nNew Delhi nIndia'

Size of String  Python determines the size of string as the count of characters in the string. For example size of string “xyz” is 3 and of “welcome” is 7. But if your string literal has an escape sequence contained in it then make sure to count the escape sequence as one character. For e.g.  You can check these size using len() function of Python. For example  >>>len(„abc ) ‟ and press enter, it will show the size as 3 String Size „‟ 1 „abc‟ 3 „ab‟ 2 “Meera‟s Toy” 11 “Vicky‟s” 7

Size of String  For multiline strings created with triple quotes : while calculating size the EOL character as the end of line is also counted in the size. For example, if you have created String Address as: >>> Address="""Civil lines Kanpur""" >>> len(Address) 18  For multiline string created with single/double quotes the EOL is not counted. >>> data="ab bc cd" >>> len(data) 6

Numeric Literals  The numeric literals in Python can belong to any of the following numerical types: 1)Integer Literals: it contain at least one digit and must not contain decimal point. It may contain (+) or (-) sign. 🞑 Types of Integer Literals: a) Decimal : 1234, -50, +100 b)Octal : it starts from symbol 0o (zero followed by letter ‘o’)  For e.g. 0o10 represent decimal 8

Numeric Literals >>> num = 0o10 >>> print(num) It will print the value 8 c) Hexadecimal : it starts from 0x (zero followed by letter ‘x’) >>> num = 0oF >>> print(num) it will print the value 15

Numeric Literals  2) Floating point Literals: also known as real literals. Real literals are numbers having fractional parts. It is represented in two forms Fractional Form or Exponent Form  Fractional Form: it is signed or unsigned with decimal point 🞑 For e.g. 12.0, -15.86, 0.5, 10. (will represent 10.0)  Exponent Part: it consists of two parts “Mantissa” and “Exponent”. 🞑 For e.g. 10.5 can be represented as 0.105 x 102 = 0.105E02 where 0.105 is mantissa and 02 (after letter E) is exponent

Points to remember <class 'tuple'>  Numeric values with commas are not considered int or float value, rather Python treats them as tuple. Tuple in a python is a collection of values or sequence of values. (will be discussed later on)  You can check the type of literal using type() function. For e.g. >>> a=100 >>> type(a) <class 'int'> >>> b=10.5 >>> type(b) <class 'float'> >>> name="hello“ >>> type(name) <class 'str'> >>> a=100,50,600 >>> type(a)

Boolean Literals A Boolean literals in Python is used to represent one of the two Boolean values i.e. True or False These are the only two values supported for Boolean Literals For e.g. >>> isMarried=True >>> type(isMarried) <class 'bool'>

Special Literals None Python has one special literal, which is None. It indicate absence of value. In other languages it is knows as NULL. It is also used to indicate the end of lists in Python. >>> salary=None >>> type(salary) <class 'NoneType'>

Complex Numbers Complex: Complex number in python is made up of two floating point values, one each for real and imaginary part. For accessing different parts of variable (object) x; we will use x.real and x.image. Imaginary part of the number is represented by “j” instead of “I”, so 1+0j denotes zero imaginary. part. Example >>> x = 1+0j >>> print x.real,x.imag 1.0 0.0 Example >>> y = 9-5j >>> print y.real, y.imag 9.0 -5.0

Conversion from one type to another  Python allows converting value of one data type to another data type. If it is done by the programmer then it will be known as type conversion or type casting and if it is done by compiler automatically then it will be known as implicit type conversion. Example of Implicit type conversion >>> x = 100 >>> type(x) <type 'int'> >>> y = 12.5 >>> type(y) <type 'float'> >>> x=y >>> type(x) <type 'float'> # Here x is automatically converted to float

Conversion from one type to another Explicit type conversion T o perform explicit type conversion Python provide functions like int(), float(), str(), bool() >>> a=50.25 >>> b=int(a) >>> print b 50 Here 50.25 is converted to int value 50 >>>a=25 >>>y=floa

Simple Input and Output  In python we can take input from user using the built-in function input().  Syntax variable = input(<message to display>) Note: value taken by input() function will always be of String type, so by default you will not be able to perform any arithmetic operation on variable. >>> marks=input("Enter your marks ") Enter your marks 100 >>> type(marks) <class 'str'> Here you can seeeven we are entering value 100 but it will be treated as string and will not allow any arithmetic operation

Simple Input and Output >>> salary=input("Enter your salary ") Enter your salary 5000 >>> bonus = salary*20/100 Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: unsupported operand type(s) for /: 'str' and 'int'

Reading / Input of Numbers  Now we are aware that input() function value will always be of string type, but what to do if we want number to be entered. The solution to this problem is to convert values of input() to numeric type using int() or float() function.

Possible chances of error while taking input as numbers 1. Entering float value while converting to int >>> num1=int(input("Enter marks ")) Enter marks 100.5 Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: invalid literal for int() with base 10: '100.5‘ 2. Entering of values in words rather than numeric >>> age=int(input("What is your age ")) What is your age Eighteen Traceback (most recent call last):

Possible chances of error while taking input as numbers 3. While input for float value must be compatible. For e.g. Example 1 >>> percentage=float(input("Enter percentage ")) Enter percentage 12.5.6 Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: could not convert string to float: '12.5.6' Example 2 >>> percentage=float(input("E nter percentage ")) Enter percentage 100 percent Traceback (most recent call last): File "<stdin>", line 1, in <module> ValueError: could not convert string to float: „100 percent'

Program 1 Open a new script file and type the following code: num1=int(input("Enter Number 1 ")) num2=int(input("Enter Number 2 ")) num3 = num1 + num2 print("Result =",num3) Save and execute by F5 and

Let us write few programs  WAP to enter length and breadth and calculate area of rectangle  WAP to enter radius of circle and calculate area of circle  WAP to enter Name, marks of 5 subject and calculate total & percentage of student  WAP to enter distance in feet and convert it into inches  WAP to enter value of temperature in Fahrenheit and convert it into Celsius.  WAP to enter radius and height of cylinder and calculate volume of cylinder.

Operator s  are symbol that perform specific operation when applied on variables. Take a look at the expression: (Operator) 10 + 25 (Operands) Above statement is an expression (combination of operator and operands) i.e. operator operates on operand. some operator requires two operand and some requires only one operand to operate

Types of Operators  Unary operators: are those operators that require one operand to operate upon. Following are some unary operators: Operator Purpose + Unary plus - Unary minus ~ Bitwise complement Not Logical negation

Types of Operators  Binary Operators:are those operators that require two upon. Following are some Binary operand to operate operators: 1. Arithmetic Operators Operator Action + Addition - Subtraction * Multiplication / Division % Remainder ** Exponent / / Floor division

Exampl e >>> num1=20 >>> num2=7 >>> val = num1 % num2 >>> print(val) 6 >>> val = 2**4 >>> print(val) 16 >>> val = num1 / num2 >>> print(val) 2.85714285714285 7 >>> val = num1 / /

Bitwise operator Operator Purpose Action & Bitwise AND Return 1 if both inputs are 1 ^ Bitwise XOR Return 1, if the number of 1 in input is in odd | Bitwise OR Return 1 if any input is 1 Bitwise operator works on the binary value of number not on the actual value. For example if 5 is passed to these operator it will work on 101 not on 5. Binary of 5 is 101, and return the result in decimal not in binary.

Exampl e Binary of 12 is 1100 and 7 is 0111, so applying & 1100 0111 ------- 0100 Which is equal to decimal value 4 Guess the output with | and ^ ? Let us see one practical example, T o check whether entered number is divisible of 2 (or in a power of 2 or not) like 2, 4, 8, 16, 32 and so on T o check this, no need of loop, simply find the bitwise & of n and n-1, if the result is 0 it means it is in power of 2 otherwise not Here we can see 0, it means 32 is in power of 2 Here we can see 16, it means 24 is not in power of 2 Later on by using „if‟ we can print meaningful message

Identity Operators Operators Purpose << Shift left >> Shift right Operators Purpose is Is the Identity same? is not Is the identity not same?

Relational Operators Operators Purpose < Less than > Greater than <= Less than or Equal to >= Greater than or Equal to == Equal to != Not equal to

Logical Operators Operators Purpose and Logical AND or Logical OR not Logical NOT

Assignment Operators Operators Purpose = Assignment / = Assign quotient += Assign sum -= Assign difference *= Assign product **= Assign Exponent / / = Assign Floor division

Membership Operators Operators Purpose in Whether variable in sequence not in Whether variable not in sequence

Punctuato rs  Punctuators are symbols that are used in programming languages to organize sentence structure, and indicate the rhythm and emphasis of expressions, statements, and program structure.  Common punctuators are: „ “ # $ @ []{}=:;(),.

Barebones of Python Program  It means basic structure of a Python program  Take a look of following code: #This program shows a program‟s component # Definition of function SeeYou() follows def SeeYou(): print(“This is my function”) #Main program A=10 B=A+20 C=A+B if(C>=100) #checking condition print(“Value is equals or more than 100”) else: print(“Value is less than 100”) SeeYou() #Calling Function Commen ts Functio n Stateme nts Expressio ns Inline Comment Bloc k Indentatio n

Expressio n  An expression is any legal combination of symbols that represents a value. An expression is generally a combination of operators and operands Example: expression of values only 20, 3.14 Expression that produce a value when evaluated A+10 Salary * 10 / 100

Statemen t  It is a programming instruction that does something i.e. some action takes place.  Example print(“Welcome to python”) The above statement call print function When an expression is evaluated a statement is executed i.e. some action takes place. a=100 b = b + 20

Comme nts addition al informationwritten in a  Comments are program which is not executed by interpreter i.e. ignored by Interpreter. Comment contains information regarding statements used, program flow, etc.  Comments in Python begins from #  Python supports 3 ways to enter comments: 1. Full line comment 2. Inline comment 3. Multiline comment

Comme nts  Full line comment Example: #This is program of volume of cylinder  Inline comment Example # calculating area of rectangle area = length*breadth  Multiline comment Example 1 (using #) # Program name: area of circle # Date: 20/07/18 #Language : Python

Comme nts  Multiline comment (using “ “ “) triple quotes Example “ “ “ Program name : swapping of two number Date Logi c : 20/07/18 : by using third variable FF F

Function s  Function is a block of code that has name and can be reused by specifying its name in the program where needed. It is created with def keyword. Example def drawline(): print(“======================“) print(“Welcome to PythonF) drawline() print(“Designed by Class XIF) drawline()

Block and Indentation  Group of statement is known as block like function, conditions or loop etc.  For e.g. def area(): a = 10 b = 5 c = a * b Indentation means extra space before writing any statement. Generally four space together marks the next indent level.

Variable s  Variables are named temporary location used to store values which can be further used in calculations, printing result etc. Every variable must have its own Identity, type and value. Variable in python is created by simply assigning value of desired type to them.  For e.g  Num = 100  Name=“JamesF

Variable s  Note: Python variables are not storage containers like other programming language. Let us analyze by example.  In C++, if we declare a variable radius: radius = 100 [suppose memory address is 41260] Now we again assign new value to radius radius = 500 Now the memory address will be still same only value will change

Variable s  Now let us take example of Python: radius = 100 [memory address 3568] radius = 700 [memory addres s 8546] Now you can see that In python, each time you assign new value to variable it will not use the same memory address and new memory will be assigned to variable. In python the location they refer to changes every time their value change.(This rule is not for all types of variables)

Lvalues and Rvalues  Lvalue : expressionthat comes on the Left hand Side of Assignment.  Rvalue : expression that comes on the Right hand Side of Assignment Lvalue refers to object to which you can assign value. It refers to memory location. It can appear LHS or RHS of assignment Rvalue refersto the value we assign to any variable.It can appear on RHS of assignment

Lvalues and Rvalues For example (valid use of Lvalue and Rvalue) x = 100 y = 200 Invalid use of Lvalue and Rvalue 100 = x 200 = y a+b = c Note: values cannot comes to the left ofassignment. LHS must be a memory location

Multiple Assignments  Python is very versatile with assignments. Let‟s see in how different ways we can use assignment in Python: 1. Assigning same value to multiple variable a = b = c = 50 2. Assigning multiple values to multiple variable a,b,c = 11,22,33 Note: While assigningvaluesthrough multiple assignment,remember that Python first evaluates the RHS and then assigns them to LHS Examples:

Multiple Assignments #Statement 1 #Statement 2 x,y,z = 10,20,30 z,y,x = x+1,z+10,y-10 print(x,y,z) Output will be 10 40 11 Now guess the output of following code fragment x,y = 7,9 y,z = x-2, x+10 print(x,y,z)

Multiple Assignments Let us take another example y, y = 10, 20 In above code first it will assign 10 to y and again it assign 20 to y, so if you print the value of y it will print 20 Now guess the output of following code x, x = 100,200 y,y = x + 100, x +200 print(x,y)

Variable definition  Variable in python is create when you assign value to it i.e. a variable is not create in memory until some value is assigned to it.  Let us take as example(if we execute the following code) print(x) Python will show an error „x‟ not defined So to correct the above code: x=0 print(x) #now it will show no

Dynamic Typing  In Python, a variable declared as numeric type can be further used to store string type or another.  Dynamic typing means a variable pointing to a value of certain type can be made to point to value/object of different type.  Lets us understand with example x = 100 print(x) x=“KVians ” print(x) # numeric type # now x point to string type

Dynamic Typing x x=1 0 0 x=“K Vians” x int: 100 int:10 0 string:KVian s

Caution with Dynamic Typing  Always ensure correct operation during dynamic typing. If types are not used correctly Python may raise an error . Take an example x = 100 y = 0 y = x / 2 print(y) x='Exam '

Determining type of variable  Python provides type() function to check the datatype of variables. >>> salary=100 >>> type(salary) <class 'int'> >>> salary=2000.50 >>> type(salary) <class 'float'> >>> name="raka" >>> type(name) <class 'str'>

Output through print()  Python allows to display output using print().  Syntax: print(message_to_print[,sep=“string”,end=“string”] ) Example 1 print(“Welcom e”) Example 2 Age=20 print(“Your age is “, Age)

Output through print() Example 3 r = int(input("Enter Radius ")) print("Area of circle is ",3.14*r*r) Note: from the Example 2 and Example 3 we can observe that while printing numeric value print() convert it into equivalent string and print it. In case of expression (Example 3) it first evaluate it and then convert the result to string before printing.

Output through print() Note: print() automatically insert space between different values given in it. The default argument of sep parameter of print() is space(‘ ‘) . Example print(“Name is”,”Vicky”) Output Name is Vicky

Output through print() Note: Python allows to change the separator string. Example print(“Name is”,”Vicky”,”Singh”,sep=“##”) Output Name is ##Vicky##Singh

Output through print() Note: Be defaulteach printstatement print the value to next line. The default value of end is “ n” Example print(“Learning Python”) print(“Developed by Guido Van Rossum”) Output Learning Python Developed by Guido Van Rossum

Output through print() Note: We can change the value of end to any other value. Example print(“Learning Python”,end=“ “) print(“Developed by Guido Van Rossum”) Output Learning Python Developed by Guido Van Rossum

Output through print() Can you Guess the output Name=“James” Salary=20000 Dept=“IT” print(“Name is “,Name,end=“@”) print(Dept) print(“Salary is “,Salary)

Just a minute…  What is the difference between keywords and identifiers  What are literals in Python? How many types of literals in python?  What will be the size of following string „a‟ , “a” , “Reena‟s”, „”‟, “It‟s”, “XY , “ “ “XY⮠ YZ” YZ”””  How many types of String in python?

Just a minute…  What are the different ways to declare multiline String?  Identify the type of following literal: 41.678, 12345, True,„True , ‟ “False”, 0xCAFE, 0o456,0o971  Difference between Expression and Statement  What is the error inn following python program: print(“Name is “, name) Suggest a solution

Just a minute…  Which of the following string will be the syntactically correct? State reason. 1. “Welcome to IndiaF 2. „He announced “Start the matchF very loudly‟ 3. “Sayonara‟ 4. „Revise Python Chapter 1‟ 5. “Bonjour 6. “Honesty is the „best‟ policyF

Just a minute…  The following code is not giving desired output. We want to enter value as 100 and obtain output as 200. Identify error and correct the program num = input("enter any number") double_num = num * 2 Print("Double of",num,"is",double_num)

Just a minute…  Why the following code is giving error? Name="James" Salary=2000 0 Dept="IT" print("Name is ",Name,end='@') print(Dept) print("Salary is ",Salary)

Just a minute…  WAP to obtain temperature in Celsius and convert it into Fahrenheit.  What will be the output of following code: x, y = 6,8 x,y = y, x+2 print(x,y)  What will be the output of following code: x,y = 7,2 x,y,x = x+4, y+6, x+100 print(x,y)

CH-3 FEATURES OF PYTHON, data types token

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