SEQUENCES:STRINGS,LISTS AND TUPLES

SEQUENCES Are items that are ordered sequentially and

accessible via index offsets into its set of elements.

Examples: strings, lists and tuples String – consists of a sequence of characters

String =“Hello” The first character of string “Hello” is ‘H’

H E L L O0 1 2 3 4

-5 -4 -3 -2 -1

Figure2-1:How sequence of elements are stored and accessed

CONTINUE.. Sequence types works with all standard type

operators (*,/,+,**) There are operators belongs to sequence type

operators as below:Sequence operator

Function

seq[ind] Element located at index ind of seqseq[ind1:ind2] Elements from ind1 up to but not

including ind2 of seqseq * expr seq repeated expr timesseq1 + seq2 Concatenates sequences seq1 and

seq2Obj in seq Tests if obj is a member of sequence

seqObj not in seq Tests if obj is not a member of

sequence seq

STRINGS Strings can be created by enclosing

characters in quotes. Single ‘ ’, double ‘” ” are same in Python Python used raw_string operator to create

literal quotes Strings are a literal or scalar type means that

they are treated by the interpreter as a singular value and not are not containers that hold other Python objects.

String are immutable meaning that changing an element of a string requires creating a new string.

CREATING AND ASSIGNING STRINGS Can assign using scalar value or having str ( )

factory function make one and assigning it to a variable.

examples:>>> aString =‘Hello world!’>>> anotherString =“Python is cool!”Print aStringHello world>>>anotherString‘Python is cool!’>>> s=str(range(4))>>> s‘[0,1,2,3]’

UPDATE STRING String can be update by reassigning a

variable to another string. The new value can be related to its previous

value or to a completely new string Example:>>>aString =‘Hello World!’>>>aString=aString[:6] +’Python!’>>> aString‘Hello Python!’>>>aString =‘new string’>>>aString‘new string’

REMOVE CHARACTERS AND STRINGS Recall- string are immutable meaning that it

individual characters cannot be remove from an existing string.

To allow this, the string needs to be empty or put together another string that drops the pieces that were not interested in.

Example: we want to remove one letter from “Hello World!”, sat letter l.

>>>aString =‘Hello World!’>>>aString= aString[:3]+aString[4:]>>>aString‘Helo World!’

CONTINUE.. To clear or remove a string, assign an empty

string or use the del statement. Examples:>>>aString=‘ ‘>>>aString‘ ‘>>>del aString

STRINGS AND OPERATORS>>> str1=‘abc’>>>str2=‘lmn’>>>str3=‘xyz’>>>str1<str2True>>>str2 !=str3True>>>str1<str3 and str2==‘xyz’False

Strings are compared

lexicographically (ASCII value

order)

MEMBERSHIP 2 operators –in, not in The membership asks whether a string / sub

string appears in another string. If that character appears in the string, return

True else False Membership operation is not used to

determine if a substring is within a string. To determine substring in string used the

string methods or string module functions such as find()/index() (and their brethren rfind() and rindex()).

CONTINUE..>>> ‘bc’ in ‘abcd’True>>>’n’ in ‘abcd’False>>>’nm’ not in ‘abcd’True

BUILT-IN FUNCTIONS Standard type functions – cmp()

Similar to value comparison operators, the cmp() build-in function also performs a lexicographic (ASCII value –based) comparison for strings.

>>>str1=‘abc’>>>str2=‘lmn’>>>str3=‘xyz’>>>cmp(str1,str2)-11 [ 97-108=-11, based on character a=97,

l=108]>>>cmp(str3,str1)23 >>>cmp(str2,’lmn’)0

CONTINUE Sequence type

functions – len() Returns the number

of characters in the string

>>>str1 = ‘abc’>>>len(str1)3>>>len(‘Hello world!’)12 max() and min()>>> str2=‘lmn’>>>str3=‘xyz’>>>max(str2)‘n’>>>min(str3)‘x’

Max() return the greatest value and min() the smallest

value of characters in strings based on

lexicographic order

>>> min(‘abc12cd’‘1’>>>min(‘ABCDabcd’)‘A’

CONTINUE enumerate() - Return an enumerate objectExample:s=‘foobar’>>>For i,t in enumerate (s):

print i,t0 f1 o2 03 b4 a5 r

Assign ‘foobar’ to s-enumerate

object

CONTINUE zip() - This function returns a list of tuples>>> s,t=‘foa’, ’obr’>>>zip(s,t)[(‘f’,’o’,),(‘o’,’b’),(‘a’,’r’)]

f O a o b r

CONTINUE String type functions

raw_input() – prompts the user with a given string and accepts and returns a user-input string.

>>>user_input = raw_input(“Enter your name: “)

Enter your name: John Doe>>>user_input‘John Doe’>>>len(user_input)8

Use input for entering NUMBER

Use raw_input for entering string

INPUT AND VARIABLES

num = input("Type in a Number: ")str = raw_input("Type in a string:")

print "num =", numprint "num * 2 =",num*2print "str =", strprint "str * 2 =",str*2IMPORTANT

OUTPUT :

Type in a Number: 12.34Type in a String: Hellonum = 12.34num * 2 = 24.68str = Hellostr * 2 = HelloHello

CONTINUE.. num variable gets data from input str variable gets data from raw_input If you want the user to type in a number use input because it returns a number

If you want the user to type in a string use raw_input because it returns a string

CONTINUE.. Numbers are of type int or float (which are

short for ’integer’ and ’floating point’ respectively) Strings are of type string Integers and floats can be worked on by

mathematical functions, strings cannot.

EXAMPLE #This programs calculates rate and distance problems

print "Input a rate and a distance"rate = input("Rate:")distance = input("Distance:")print "Time:",distance/rate

OUTPUT :Input a rate and a distanceRate:5Distance:10Time: 2

CONTINUE..

5

ratedistance

10

10/5=2

time = distance/rateVariables

Variables

EXERCISE 1

As a programmer you were asked to write a program that accepts user name, age and gender. Display user name, age and gender.

Based on the given problem: Identify the input

Determine the data type for each input /output Identify the output Design the solution using flowchart and

pseudocode Transform the design to Python language

EXERCISE 2 As a programmer, you were asked to write a

program that able to compare the two input strings. Your program must allow user to input both strings and make a comparison on which string is bigger that the other. Based on the given problem: Identify the input Identify the output Design the solution using flowchart and

pseudocode Transform the design to Python language

EXERCISE 3 Write a program to convert an input number of

nickels and dime into a total number of cents. For example, if the user inputs 3 and 7 for the number of nickels and dimes, respectively, the screen display at the end of the run would be :

Enter number of nickels and dimes 3 7Example output:3 nickels and 7 dimes = 85 cents.

Design the solution with flowchart and transform the flowchart into Python’s code

EXERCISE 4 Design a program using list that allow user to

input 5 numbers in a lists and get the average value.

Design your solution with a pseudocode and transform the design to Python’s code.