UNIT-III. All expressions involving relational and logical operators will evaluate to either true or false

Transcription

1 UNIT-III BOOLEAN VALUES AND OPERATORS: A boolean expression is an expression that is either true or false. The following examples use the operator ==, which compares two operands and produces if they are equal and False otherwise: >>> 5 == 5 >>> 5 == 6 False and False are special values that belong to the type bool; they are not strings: >>> type() <class 'bool'> >>> type(false) <class 'bool'> The == operator is one of the relational operators; the others are: x!= y # x is not equal to y x > y # x is greater than y x < y # x is less than y x >= y # x is greater than or equal to y x <= y # x is less than or equal to y Note: All expressions involving relational and logical operators will evaluate to either true or false CONDITIONAL (IF): The if statement contains a logical expression using which data is compared and a decision is made based on the result of the comparison. Syntax : if expression: If the boolean expression evaluates to TRUE, then the block of inside the if statement is executed. If boolean expression evaluates to FALSE, then the first set of code after the end of the if is executed. a=10 if a>9: print( A is Greater than 9 ) Output: A is Greater than 9

2 ALTERNATIVE IF(IF-ELSE): An else statement can be combined with an if statement. An else statement contains the block of code (false block) that executes if the conditional expression in the if statement resolves to 0 or a FALSE value. The else statement is an optional statement and there could be at most only one else statement following if. if expression: Flowchart: Example Output B is Greater than A a=10 b=20 if a>b: print( A is Greater than B ) print( B is Greater than A ) CHAINED CONDITIONAL IF:(IF-ELIF-ELSE) The elif statement allows us to check multiple expressions for TRUE and execute a block of code as soon as one of the conditions evaluates to TRUE. Similar to the else, the elif statement is optional. However, unlike else, for which there can be at most one statement, there can be an arbitrary number of elif statements following an if. if expression1: elif expression2: elif expression3:

3 Flowchart: var = 100 if var == 200: print 1 - Got a true expression value print var elif var == 150: print 2 - Got a true expression value print var elif var == 100: Output: print 3 - Got a true expression value print var print 4 - Got a false expression value print var print Good bye! 3 - Got a true expression value 100 Good bye! Nested Conditionals: One conditional can also be nested within another.

4 if expression1: if expression2: Flowchart: num = float(input( Enter a number: )) if num >= 0: if num == 0: print( Zero ) print( Positive number ) print( Negative Output: number ) Enter a number: 5 Positive number

5 ITERATION: A loop statement allows us to execute a statement or group of statements multiple times. Repeated execution of a set of statements with the help of loops is called iteration. WHILE LOOP: A while loop statement executes a block of statement again and again until the condition will occur false (or) Repeats a statement or group of statements while a given condition is TRUE. It tests the condition before executing the loop body so this technique is known as Entry controlled loop. while expression: Flowchart: count = 0 while (count < 9): print The count is:, count count = count + 1 print Good bye! FOR LOOP: Executes a sequence of statements multiple times for iterating_var in sequence: statements(s)

6 If a sequence contains an expression list, it is evaluated first. Then, the first item in the sequence is assigned to the iterating variable iterating var. Next, the statements block is executed. Each item in the list is assigned to iterating_var, and the block is executed until the entire sequence is exhausted. Flowchart: for letter in Python : print Current Letter :, letter Output: Current Letter : P Current Letter : y Current Letter : t Current Letter : h Current Letter : o Current Letter : n BREAK : Terminates the loop statement and transfers execution to the statement immediately following the loop. The break statement can be used in both while and for loops. for letter in Python : # First Example if letter == h : break print Current Letter :, letter Output: Current Letter : P Current Letter : y Current Letter : t

7 CONTINUE: It returns the control to the next iteration of the loop. The continue statement rejects all the remaining statements in the current iteration of the loop. The continue statement can be used in both while and for loops. for letter in Python : # First Example if letter == h : continue print Current Letter :, letter Output: Current Letter : P Current Letter : y Current Letter : t Current Letter : o Current Letter : n PASS: The pass statement is a null operation; nothing happens when it executes. The pass is also useful in places where your code will eventually go, but has not been written yet for letter in Python : if letter == h : pass print This is pass block print Current Letter :, letter print Good bye! Output: Current Letter : P Current Letter : y Current Letter : t This is pass block Current Letter : h Current Letter : o Current Letter : n Good bye! FRUITFUL FUNCTIONS vs VOID FUNCTIONS: Any function that returns a value is called Fruitful function. A Function that does not return a value is called a void function *Write any example for both Fruitful and void functions

8 RETURN VALUES: The Keyword return is used to return back the value to the called function. def area(radius): b = * radius**2 return b VARIABLE SCOPE: Global Scope: A variable which is defined in the main body of a file is called a global variable. It will be visible throughout the file, and also inside any file which imports that file. Local Scope: A variable which is defined inside a function is local to that function. It is accessible from the point at which it is defined until the end of the function, and exists for as long as the function is executing # This is still a global variable b = 1 def my_function(c): # this is a local variable d = 3 print(c) print(d) FUNCTION COMPOSITION: Calling a function within another function is called as Function Composition. The output of one function is given as input to another function colors=('red','green','blue') >>> fruits=['orange','banana','cherry'] >>> zip(colors,fruits) <zip object at 0x020A00D0> >>>list(zip(colors,fruits)) [('red', 'orange'), ('green', 'banana'), ('blue', 'cherry')]

9 STRINGS A string is a sequence of characters. We can access the characters one at a time with the bracket operator: >>> fruit = 'banana' >>> letter = fruit[1] The second statement selects character number 1 from fruit and assigns it to letter. The expression in brackets is called an index. The index indicates which character in the sequence we want Strings are immutable It is tempting to use the [] operator on the left side of an assignment, with the intention of changing a character in a string. For example: >>> greeting = 'Hello, world!' >>> greeting[0] = 'J' TypeError: 'str' object does not support item assignment The reason for the error is that strings are immutable, which means we can t change an existing string. The best we can do is create a new string that is a variation on the original: >>> greeting = 'Hello, world!' >>> new_greeting = 'J' + greeting[1:] >>> new_greeting 'Jello, world! STRING SLICES: A segment of a string is called a slice. Selecting a slice is similar to selecting a character: String[start_index:end_index] >>> s = 'Monty Python' >>> s[0:5] 'Monty' >>> s[6:12] 'Python If you omit the first index (before the colon), the slice starts at the beginning of the string.if you omit the second index, the slice goes to the end of the string: >>> fruit = 'banana' >>> fruit[:3] If the first index is greater than or equal to the second the result is an empty string, represented by two quotation marks: >>> fruit = 'banana' >>> fruit[3:3] [ ]

10 STRING METHODS: S.no Method name Description 1. isalnum() Returns true if string has at least 1 character and all characters are alphanumeric and false otherwise. 2. isalpha() Returns true if string has at least 1 character and all characters are alphabetic and false otherwise. 3. isdigit() Returns true if string contains only digits and false otherwise. 4. islower() Returns true if string has at least 1 cased character and all cased characters are in lowercase and false otherwise. 5. isnumeric() Returns true if a string contains only numeric characters and false otherwise. 6. isspace() Returns true if string contains only whitespace characters and false otherwise. 7. istitle() Returns true if string is properly titlecased and false otherwise. 8. isupper() Returns true if string has at least one cased character and all cased characters are in uppercase and false otherwise. 9. replace(old, new [, max]) Replaces all occurrences of old in string with new or at most max occurrences if max given. 10. split() Splits string according to delimiter str (space if not provided) and returns list of substrings; 11. count() Occurrence of a string in another string 12. find() Finding the index of the first occurrence of a string in another string 13. swapcase() Converts lowercase letters in a string to uppercase and viceversa 14. startswith(str, beg=0,end=len(string)) Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwise. Note: All the string methods will be returning either true or false as the result 1.isalnum(): Isalnum() method returns true if string has at least 1 character and all characters are alphanumeric and false otherwise. String.isalnum() >>> string="123alpha" >>> string.isalnum()

11 2.isalpha(): isalpha() method returns true if string has at least 1 character and all characters are alphabetic and false otherwise. String.isalpha() >>> string="nikhil" >>> string.isalpha() 3.isdigit(): isdigit() returns true if string contains only digits and false otherwise. String.isdigit() >>> string=" " >>> string.isdigit() 4.islower(): Islower() returns true if string has characters that are in lowercase and false otherwise. String.islower() >>> string="nikhil" >>> string.islower() 5.isnumeric(): isnumeric() method returns true if a string contains only numeric characters and false otherwise. String.isnumeric() >>> string=" " >>> string.isnumeric() 6. isspace(): isspace() returns true if string contains only whitespace characters and false otherwise. String.isspace() >>> string=" " >>> string.isspace()

12 7.istitle() istitle() method returns true if string is properly titlecased (starting letter of each word is capital) and false otherwise String.istitle() >>> string="nikhil Is Learning" >>> string.istitle() 8.isupper() isupper() returns true if string has characters that are in uppercase and false otherwise. String.isupper() >>> string="hello" >>> string.isupper() 9.replace() replace() method replaces all occurrences of old in string with new or at most max occurrences if max given. String.replace() >>> string="nikhil Is Learning" >>> string.replace('nikhil','neha') 'Neha Is Learning' 10.split() split() method splits the string according to delimiter str (space if not provided) String.split() >>> string="nikhil Is Learning" >>> string.split() ['Nikhil', 'Is', 'Learning'] 11.count() count() method counts the occurrence of a string in another string String.count() >>> string='nikhil Is Learning' >>> string.count('i') 3

13 12. find() Find() method is used for finding the index of the first occurrence of a string in another string String.find( string ) >>> string="nikhil Is Learning" >>> string.find('k') swapcase() converts lowercase letters in a string to uppercase and viceversa String.find( string ) >>> string="hello" >>> string.swapcase() 'hello' 14. startswith() Determines if string or a substring of string (if starting index beg and ending index end are given) starts with substring str; returns true if so and false otherwise. String.startswith( string ) >>> string="nikhil Is Learning" >>> string.startswith('n') 15.endswith() Determines if string or a substring of string (if starting index beg and ending index end are given) ends with substring str; returns true if so and false otherwise. String.endswith( string ) >>> string="nikhil Is Learning" >>> string.startswith('g')

14 STRING MODULE: This module contains a number of functions to process standard Python strings. In recent versions, most functions are available as string methods as well. Example : import string text = Monty Python s Flying Circus print upper, =>, string.upper(text) print lower, =>, string.lower(text) print split, =>, string.split(text) print join, =>, string.join(string.split(text), + ) print replace, =>, string.replace(text, Python, Java ) print find, =>, string.find(text, Python ), string.find(text, Java ) print count, =>, string.c ount(text, n ) ILLUSTRATIVE PROGRAMS: 1. FINDING SQUARE ROOT OF A GIVEN NUMBER while : print("enter x for exit.") num = input("enter a number: ") #input Number if num == 'x': break number = float(num) number_sqrt = number ** 0.5 #compute square root print('square Root of %0.2f is %0.2f' %(number, number_sqrt)) 2. FINDING GCD OF A NUMBER def gcd(a,b): if(b==0): return a return gcd(b,a%b) a=int(input( Enter first number: )) b=int(input( Enter second number: )) GCD=gcd(a,b) print( GCD is: ) print(gcd)

15 Output Case 1: Enter first number:5 Enter second number:15 GCD is: 5 Sum the array of numbers def listsum(numlist): if len(numlist) == 1: return numlist[0] return numlist[0] + listsum(numlist[1:]) print(listsum([1,3,5,7,9])) Output 25 LINEAR SEARCH: def sequentialsearch(alist, item) pos = 0 found = False while pos < len(alist) and not found: if alist[pos] == item: found = pos=pos+1 return found testlist = [1, 2, 32, 8, 17, 19, 42, 13, 0] print(sequentialsearch(testlist, 3)) print(sequentialsearch(testlist, 13)) Output False

16 BINARY SEARCH def binarysearch(alist, item): first = 0 last = len(alist)-1 found = False while first<=last and not found: midpoint = (first + last)//2 if alist[midpoint] == item: found = if item < alist[midpoint]: last = midpoint-1 first = midpoint+1 return found testlist = [0, 1, 2, 8, 13, 17, 19, 32, 42,] print(binarysearch(testlist, 3)) print(binarysearch(testlist, 13))