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Class 11 - Computer Science with Python Sumita Arora
String Manipulation

Chapter 10
String Manipulation
Class 11 - Computer Science with Python Sumita Arora

Multiple Choice Questions
Question 1
Negative index -1 belongs to .......... of string.

first character
last character ✓
second last character
second character
Question 2
Which of the following is/are not legal string operators?

in
+
*
/ ✓
Question 3
Which of the following functions will return the total number of characters in a string?

count()
index()
len() ✓
all of these
Question 4
Which of the following functions will return the last three characters of a string s?

s[3:]
s[:3]
s[-3:] ✓
s[:-3]
Question 5
Which of the following functions will return the first three characters of a string s?

s[3:]
s[:3] ✓
s[-3:]
s[:-3]
Question 6
Which of the following functions will return the string in all caps?

upper() ✓
toupper()
isupper()
to-upper()
Question 7
Which of the following functions will return the string with every 'P' replaced with a 'z'?

find()
index()
replace() ✓
split()
Question 8
Which of the following functions will return a list containing all words of the string?

find()
index()
partition()
split() ✓
Question 9
Which of the following functions will always return a tuple of 3 elements?

find()
index()
partition() ✓
split()
Question 10
What is the output of the following code?

str1 = "Mission 999"
str2 = "999"
print(str1.isdigit(),str2.isdigit())
False True ✓
False False
True False
True True
Question 11
Choose the correct function to get the ASCII code of a character.

char('char')
ord('char') ✓
ascii('char')
All of these
Question 12
Which method should I use to convert String "Python programming is fun" to "Python Programming Is Fun" ?

capitalize()
title() ✓
istitle()
upper()
Question 13
Guess the correct output of the following String operations.

str1 = 'Wah'
print(str1*2)
WahWah ✓
TypeError: unsupported operand type(s) for * : 'str' and 'int'
WWaahh
Wah2
Question 14
What is the output of the following string operation?

str = "My roll no. is 12"
print(str.isalnum())
True
False ✓
Error
No output
Question 15
Select the correct output of the following String operations.

str1 = 'Waha'
print(str1[:3] + 'Bhyi' + str1[-3:])
Wah Bhyi Wah
WahBhyiaha ✓
WahBhyiWah
WahBhyiWaha
Question 16
Select the correct output of the following String operations.

str = "my name is Anu John"
print(str.capitalize())
'My name is anu john' ✓
TypeError: unsupported operand type(s) for * : 'str' and 'int'
'My name is Anu John'
'My Name Is Anu John'
Question 17
Choose the correct function to get the character from ASCII number.

ascii(number)
char(number)
chr(number) ✓
all of these
Question 18
s = ' '(single space). Then s.isalnum() will return.

True
False ✓
Error
nothing
Question 19
Which of the following functions removes all leading and trailing spaces from a string?

lstrip()
rstrip()
strip() ✓
all of these
Question 20
Which of the following functions will raise an error if the given substring is not found in the string?

find()
index() ✓
replace()
all of these
Fill in the Blanks
Question 1
The string indexes begin 0 onwards.

Question 2
For strings, + operator performs concatenation.

Question 3
For strings, * operator performs replication.

Question 4
The in and not in are membership operators for strings (in, not in).

Question 5
The ord() returns the ASCII value of a given character.

Question 6
If a string contains letters and digits, function isalnum() will return true.

Question 7
'ab'.isalpha() will return value as True.

Question 8
To get each word's first letter capitalized, title() function is used.

Question 9
Function index() raises an exception if the substring is not found.

Question 10
Function split() divides a line of text into individual words.

True/False Questions
Question 1
Strings have both positive and negative indexes.
True

Question 2
Python does not support a character type; a single character is treated as strings of length one.
True

Question 3
Strings are immutable in Python, which means a string cannot be modified.
True

Question 4
Like '+', all other arithmetic operators are also supported by strings.
False

Question 5
Functions capitalize() and title() return the same result.
False

Question 6
Functions partition() and split() work identically.
False

Question 7
The find() and index() are similar functions.
True

Question 8
The find() does not raise an exception if the substring is not found.
True

Question 9
The partition() function's result is always a 3-element tuple.
True

Question 10
The split() returns always a 3-element list.
False

Type A : Short Answer Questions/Conceptual Questions
Question 1
Write a Python script that traverses through an input string and prints its characters in different lines — two characters per line.

Answer

str = input("Enter the string: ")
length = len(str)
for a in range(0, length, 2):
    print(str[a:a+2])
Output

Enter the string: KnowledgeBoat
Kn
ow
le
dg
eB
oa
t
Question 2
Out of the following operators, which ones can be used with strings in Python?

=, -, *, /, //, %, >, <>, in, not in, <=

Answer

The following Python operators can be used with strings:

=, *, >, in, not in, <=

Question 3
What is the result of following statement, if the input is 'Fun'?

print(input("...") + "trial" + "Ooty" * 3)

Answer

The result of the statement is:

FuntrialOotyOotyOoty

Question 4
Which of the following is not a Python legal string operation?

(a) 'abc' + 'abc'
(b) 'abc' * 3
(c) 'abc' + .3
(d) 'abc.lower()

Answer

'abc' + .3 is not a legal string operation in Python. The operands of + operator should be both string or both numeric. Here one operand is string and other is numeric. This is not allowed in Python.

Question 5
Can you say strings are character lists? Why? Why not?

Answer

Strings are sequence of characters where each character has a unique index. This implies that strings are iterable like lists but unlike lists they are immutable so they cannot be modified at runtime. Therefore, strings can't be considered as character lists. For example,

str = 'cat'
# The below statement
# is INVALID as strings
# are immutable
str[0] = 'b' 

# Considering character lists
strList = ['c', 'a', 't']
# The below statement
# is VALID as lists
# are mutable
strList[0] = 'b'
Question 6
Given a string S = "CARPE DIEM". If n is length/2 (length is the length of the given string), then what would following return?

(a) S[: n]
(b) S[n :]
(c) S[n : n]
(d) S[1 : n]
(e) S[n : length - 1]

Answer

(a) CARPE
(b) DIEM
(c) (Empty String)
(d) ARPE
(e) DIE

Question 7
From the string S = "CARPE DIEM", which ranges return "DIE" and "CAR"?

Answer

S[6:9] returns DIE
S[:3] returns CAR
Question 8
What happens when from a string slice you skip the start and/or end values of the slice?

Answer

If start value is skipped, it is assumed as 0 i.e. the slice begins from the start of the string.

If end value is skipped, it is assumed as the last index of the string i.e. the slice extends till the end of the string.

Question 9
What would the following expressions return?

"Hello World".upper( ).lower( )
"Hello World".lower( ).upper( )
"Hello World".find("Wor", 1, 6)
"Hello World".find("Wor")
"Hello World".find("wor")
"Hello World".isalpha( )
"Hello World".isalnum( )
"1234".isdigit( )
"123FGH".isdigit( )
Answer

hello world
HELLO WORLD
-1
6
-1
False
False
True
False
Explanation

upper() first converts all letters of "Hello World" to uppercase. Then "HELLO WORLD".lower() converts all letters to lowercase.
lower() first converts all letters of "Hello World" to lowercase. Then "hello world".upper() converts all letters to uppercase.
"Hello World".find("Wor", 1, 6) searches for the presence of substring "Wor" between 1 and 6 indexes of string "Hello World". Substring from 1 to 6 index is "ello W". As "Wor" is not present in this hence the result is False.
"Hello World".find("Wor") searches for the presence of substring "Wor" in the entire "Hello World" string. Substring "Wor" starts at index 6 of "Hello World" hence the result is 6.
"Hello World".find("wor") searches for the presence of substring "wor" in the entire "Hello World" string. find() performs case sensitive search so "wor" and "Wor" are different hence the result is -1.
"Hello World".isalpha( ) checks if all characters in the string as alphabets. As a space is also present in the string hence it returns False.
"Hello World".isalnum( ) checks if all characters in the string are either alphabets or digits. As a space is also present in the string which is neither an alphabet nor a string hence it returns False.
"1234".isdigit( ) checks if all characters in the string are digits or not. As all characters are digits hence the result is True.
As "FGH" in the string "123FGH" are not digits hence the result is False.
Question 10
Which functions would you choose to use to remove leading and trailing white spaces from a given string?

Answer

lstrip() removes leading white-spaces, rstrip() removes trailing white-spaces and strip() removes leading and trailing white-spaces from a given string.

Question 11
Try to find out if for any case, the string functions isalnum( ) and isalpha( ) return the same result

Answer

isalnum( ) and isalpha( ) return the same result in the following cases:

If string contains only alphabets then both isalnum( ) and isalpha( ) return True. For example, "Hello".isalpha() and "Hello".isalnum() return True.
If string contains only special characters and/or white-spaces then both isalnum( ) and isalpha( ) return False. For example, "*#".isalpha() and "*#".isalnum() return False.
Question 12
Suggest appropriate functions for the following tasks:

To check whether the string contains digits
To find for the occurrence a string within another string
To convert the first letter of a string to upper case
to capitalize all the letters of the string
to check whether all letters of the string are in capital letters
to remove from right of a string all string-combinations from a given set of letters
to remove all white spaces from the beginning of a string
Answer

isdigit()
find()
capitalize()
upper()
isupper()
rstrip(characters)
lstrip()
Question 13
In a string slice, the start and end values can be beyond limits. Why?

Answer

String slicing always returns a subsequence and empty subsequence is a valid sequence. Thus, when a string is sliced outside the bounds, it still can return empty subsequence and hence Python gives no errors and returns empty subsequence.

Question 14
Can you specify an out of bound index when accessing a single character from a string? Why?

Answer

We cannot specify an out of bound index when accessing a single character from a string, it will cause an error. When we use an index, we are accessing a constituent character of the string. If the index is out of bounds there is no character to return from the given index hence Python throws string index out of range error.

Question 15
Can you add two strings? What effect does ' + ' have on strings?

Answer

Yes two strings can be added using the '+' operator. '+' operator concatenates two strings.

Type B: Application Based Questions
Question 1a
What is the result of the following expression?

print("""
1
 2
  3
""")
Answer


1
 2
  3

Question 1b
What is the result of the following expression?

text = "Test.\nNext line."
print (text)
Answer

Test.
Next line.
Question 1c
What is the result of the following expression?

print ('One', ' Two ' * 2)
print ('One ' + 'Two' * 2)
print (len('10123456789'))
Answer

One  Two  Two 
One TwoTwo
11
Question 1d
What is the result of the following expression?

s = '0123456789'
print(s[3], ", ", s[0 : 3], " - ", s[2 : 5])
print(s[:3], " - ", s[3:], ", ", s[3:100])
print(s[20:], s[2:1], s[1:1])
Answer

3 ,  012  -  234
012  -  3456789 ,  3456789

Question 1e
What is the result of the following expression?

s ='987654321'
print (s[-1], s[-3])
print (s[-3:], s[:-3])
print (s[-100:-3], s[-100:3])
Answer

1 3
321 987654
987654 987
Question 2a
What will be the output produced by following code fragments?

y = str(123)
x = "hello" * 3
print (x, y)
x = "hello" + "world"
y = len(x)
print (y, x)
Answer

Output
hellohellohello 123
10 helloworld
Explanation
str(123) converts the number 123 to string and stores in y so y becomes "123". "hello" * 3 repeats "hello" 3 times and stores it in x so x becomes "hellohellohello".

"hello" + "world" concatenates both the strings so x becomes "helloworld". As "helloworld" contains 10 characters so len(x) returns 10.

Question 2b
What will be the output produced by following code fragments?

x = "hello" + \
"to Python" + \
"world"
for char in x :
    y = char
    print (y, ' : ', end = ' ')
Answer

Output
h  :  e  :  l  :  l  :  o  :  t  :  o  :     :  P  :  y  :  t  :  h  :  o  :  n  :  w  :  o  :  r  :  l  :  d  : 
Explanation
Inside the for loop, we are traversing the string "helloto Pythonworld" character by character and printing each character followed by a colon (:).

Question 2c
What will be the output produced by following code fragments?

x = "hello world"
print (x[:2], x[:-2], x[-2:])
print (x[6], x[2:4])
print (x[2:-3], x[-4:-2])
Answer

Output
he hello wor ld
w ll
llo wo or
Explanation
x[:2] ⇒ he
x[:-2] ⇒ hello wor
x[-2:] ⇒ ld

x[6] ⇒ w
x[2:4] ⇒ ll

x[2:-3] ⇒ llo wo
x[-4:-2] ⇒ or

Question 3
Carefully go through the code given below and answer the questions based on it :

theStr = " This is a test "         
inputStr = input(" Enter integer: ")
inputlnt = int(inputStr)            
testStr = theStr
while inputlnt >= 0 :               
    testStr = testStr[1:-1]        
    inputlnt = inputlnt - 1
testBool = 't' in testStr
print (theStr)             # Line 1 
print (testStr)            # Line 2 
print (inputlnt)           # Line 3 
print (testBool)           # Line 4 
(i) Given the input integer 3, what output is produced by Line 1?

This is a test
This is a
is a test
is a
None of these
Answer

Option 1 — This is a test

(ii) Given the input integer 3, what output is produced by Line 2?

This is a test
s is a t
is a test
is a
None of these
Answer

Option 2 — s is a t

Explanation
As input is 3 and inside the while loop, inputlnt decreases by 1 in each iteration so the while loop executes 4 times for inputlnt values 3, 2, 1, 0.

1st Iteration
testStr = "This is a test"

2nd Iteration
testStr = "his is a tes"

3rd Iteration
testStr = "is is a te"

4th Iteration
testStr = "s is a t"

(iii) Given the input integer 2, what output is produced by Line 3?

0
1
2
3
None of these
Answer

Option 5 — None of these

Explanation
Value of inputlnt will be -1 as till inputlnt >= 0 the while loop will continue executing.

(iv) Given the input integer 2, what output is produced by Line 4?

False
True
0
1
None of these
Answer

Option 2 — True

Explanation
As input is 2 and inside the while loop, inputlnt decreases by 1 in each iteration so the while loop executes 3 times for inputlnt values 2, 1, 0.

1st Iteration
testStr = "This is a test"

2nd Iteration
testStr = "his is a tes"

3rd Iteration
testStr = "is is a te"

After the while loop finishes executing, value of testStr is "is is a te". 't' in testStr returns True as letter t is present in testStr.

Question 4
Carefully go through the code given below and answer the questions based on it :

testStr = "abcdefghi"                    
inputStr = input ("Enter integer:")      
inputlnt = int(inputStr)                 
count = 2                                
newStr = ''                               
while count <= inputlnt :                
    newStr = newStr + testStr[0 : count]
    testStr = testStr[2:]      #Line 1   
    count = count + 1                    
print (newStr)                 # Line 2
print (testStr)                # Line 3  
print (count)                  # Line 4  
print (inputlnt)               # Line 5  
(i) Given the input integer 4, what output is produced by Line 2?

abcdefg
aabbccddeeffgg
abcdeefgh
ghi
None of these
Answer

Option 3 — abcdeefgh

Explanation
Input integer is 4 so while loop will execute 3 times for values of count as 2, 3, 4.

1st Iteration
    newStr = newStr + testStr[0:2]
⇒ newStr = '' + ab
⇒ newStr = ab

    testStr = testStr[2:]
⇒ testStr = cdefghi

2nd Iteration
    newStr = newStr + testStr[0:3]
⇒ newStr = ab + cde
⇒ newStr = abcde

    testStr = testStr[2:]
⇒ testStr = efghi

3rd Iteration
    newStr = newStr + testStr[0:4]
⇒ newStr = abcde + efgh
⇒ newStr = abcdeefgh

    testStr = testStr[2:]
⇒ testStr = ghi

(ii) Given the input integer 4, what output is produced by Line 3?

abcdefg
aabbccddeeffgg
abcdeefgh
ghi
None of these
Answer

Option 4 — ghi

Explanation
Input integer is 4 so while loop will execute 3 times for values of count as 2, 3, 4.

1st Iteration
    testStr = testStr[2:]
⇒ testStr = cdefghi

2nd Iteration
    testStr = testStr[2:]
⇒ testStr = efghi

3rd Iteration
    testStr = testStr[2:]
⇒ testStr = ghi

(iii) Given the input integer 3, what output is produced by Line 4?

0
1
2
3
None of these
Answer

Option 5 — None of these

Explanation
Looking at the condition of while loop — while count <= inputlnt, the while loop will stop executing when count becomes greater than inputlnt. Value of inputlnt is 3 so when loop stops executing count will be 4.

(iv) Given the input integer 3, what output is produced by Line 5?

0
1
2
3
None of these
Answer

Option 4 — 3

Explanation
The input is converted from string to integer and after that its value is unchanged in the code so line 5 prints the input integer 3.

(v) Which statement is equivalent to the statement found in Line 1?

testStr = testStr[2:0]
testStr = testStr[2:-1]
testStr = testStr[2:-2]
testStr = testStr - 2
None of these
Answer

Option 5 — None of these

Question 5
Carefully go through the code given below and answer the questions based on it :

inputStr = input(" Give me a string:")
biglnt = 0
littlelnt = 0
otherlnt = 0
for ele in inputStr:
    if ele >= 'a' and ele <= 'm':     # Line 1
        littlelnt = littlelnt + 1
    elif ele > 'm' and ele <= 'z':
        biglnt = biglnt + 1
    else:
        otherlnt = otherlnt + 1
print (biglnt)             # Line 2
print (littlelnt)          # Line 3
print (otherlnt)           # Line 4
print (inputStr.isdigit()) # Line 5
(i) Given the input abcd what output is produced by Line 2?

0
1
2
3
4
Answer

Option 1 — 0

Explanation
In the input abcd, all the letters are between a and m so the condition — if ele >= 'a' and ele <= 'm' is always true. Hence, biglnt is 0.

(ii) Given the input Hi Mom what output is produced by Line 3?

0
1
2
3
None of these
Answer

Option 3 — 2

Explanation
In the input Hi Mom, only two letters i and m satisfy the condition — if ele >= 'a' and ele <= 'm'. Hence, value of littlelnt is 2.

(iii) Given the input Hi Mom what output is produced by Line 4?

0
1
2
3
None of these
Answer

Option 4 — 3

Explanation
In the input Hi Mom, 3 characters H, M and space are not between a and z. So for these 3 characters the statement in else part — otherlnt = otherlnt + 1 is executed. Hence, value of otherlnt is 3.

(iv) Given the input 1+2 =3 what output is produced by Line 5?

0
1
True
False
None of these
Answer

Option 4 — False

Explanation
As all characters in the input string 1+2 =3 are not digits hence isdigit() returns False.

(v) Give the input Hi Mom, what changes result from modifying Line 1 from

if ele >= 'a' and ele <='m' to the expression
if ele >= 'a' and ele < 'm'?

No change
otherlnt would be larger
littlelnt would be larger
biglnt would be larger
None of these
Answer

Option 2 — otherlnt would be larger

Explanation
For letter m, now else case will be executed increasing the value of otherlnt.

Question 6
Carefully go through the code given below and answer the questions based on it :

in1Str = input(" Enter string of digits: ")
in2Str = input(" Enter string of digits: ")

if len(in1Str)>len(in2Str):
    small = in2Str
    large = in1Str
else:
    small = in1Str
    large = in2Str
newStr = ''
for element in small:
    result = int(element) + int(large[0])
    newStr = newStr + str(result)
    large = large[1:]
print (len(newStr))      # Line 1
print (newStr)           # Line 2
print (large)            # Line 3
print (small)            # Line 4
(i) Given a first input of 12345 and a second input of 246, what result is produced by Line 1?

1
3
5
0
None of these
Answer

Option 2 — 3

Explanation
As length of smaller input is 3, for loop executes 3 times so 3 characters are added to newStr. Hence, length of newStr is 3.

(ii) Given a first input of 12345 and a second input of 246, what result is produced by Line 2?

369
246
234
345
None of these
Answer

Option 1 — 369

Explanation
For loop executes 3 times as length of smaller input is 3.

1st Iteration
    result = 2 + 1
⇒ result = 3

    newStr = '' + '3'
⇒ newStr = '3'

    large = 2345

2nd Iteration
    result = 4 + 2
⇒ result = 6

    newStr = '3' + '6'
⇒ newStr = '36'

    large = 345

3rd Iteration
    result = 6 + 3
⇒ result = 9

    newStr = '36' + '9'
⇒ newStr = '369'

    large = 45

Final value of newStr is '369'.

(iii) Given a first input of 123 and a second input of 4567, what result is produced by Line 3?

3
7
12
45
None of these
Answer

Option 2 — 7

Explanation
For loop executes 3 times as length of smaller input is 3. Initial value of large is 4567.

1st Iteration
    large = large[1:]
⇒ large = 567

2nd Iteration     large = large[1:]
⇒ large = 67

3rd Iteration     large = large[1:]
⇒ large = 7

(iv) Given a first input of 123 and a second input of 4567, what result is produced by Line 4?

123
4567
7
3
None of these
Answer

Option 1 — 123

Explanation
As length of 123 is less than length of 4567 so 123 is assigned to variable small and gets printed in line 4.

Question 7a
Find the output if the input string is 'Test'.

S = input("Enter String :")
RS = " "
for ch in S :
    RS = ch + RS
print(S + RS)
Answer

Output
TesttseT
Explanation
The for loop reverses the input string and stores the reversed string in variable RS. After that original string and reversed string are concatenated and printed.

Question 7b
Find the output if the input string is 'Test'.

S = input("Enter String :")
RS = " "
for ch in S :
    RS = ch + 2 + RS
print(S + RS)
Answer

The program gives an error at line RS = ch + 2 + RS. The operands to + are a mix of string and integer which is not allowed in Python.

Question 8a
Find the errors. Find the line numbers causing errors.

S = "PURA VIDA"
print(S[9] + S[9 : 15])
Answer

The error is in line 2. Length of string S is 9 so its indexes range for 0 to 8. S[9] is causing error as we are trying to access out of bound index.

Question 8b
Find the errors. Find the line numbers causing errors.

S = "PURA VIDA"
S1 = S[: 10] +S[10 :]
S2 = S[10] + S[-10]
Answer

The error is in line 3. Length of string S is 9 so its forward indexes range for 0 to 8 and backwards indexes range from -1 to -9. S[10] and S[-10] are trying to access out of bound indexes.

Question 8c
Find the errors. Find the line numbers causing errors.

S = "PURA VIDA"
S1 = S * 2
S2 = S1[-19] + S1[-20]
S3 = S1[-19 :]
Answer

The error is in line 3. S1[-19] and S1[-20] are trying to access out of bound indexes.

Question 8d
Find the errors. Find the line numbers causing errors.

S = "PURA VIDA"
S1 = S[: 5]
S2 = S[5 :]
S3 = S1 * S2
S4 = S2 + '3'
S5 = S1 + 3
Answer

The errors are in line 4 and line 6. Two strings cannot be multiplied. A string and an integer cannot be added.

Question 9
What is the output produced?

(i) >>> "whenever" .find("never")

(ii) >>> "whenever" .find("what")

Answer

(i) 3
The starting index of substring "never" in "whenever" is 3.

(ii) -1
Substring "what" is not present in "whenever".

Question 10
What is the output produced?

(i) >>> "-".join(['123','365','1319'])

(ii) >>> " ".join(['Python', 'is', 'fun'])

Answer

(i) '123-365-1319'

(ii) 'Python is fun'

Question 11
Given a string S, write expressions to print

first five characters of S
Ninth character of S
reversed S
alternate characters from reversed S
Answer

print(S[:5])
print(S[8])
for a in range(-1, (-len(S) - 1), -1) :
      print(S[a], end = '')
for a in range(-1, (-len(S) - 1), -2) :
      print(S[a], end = '')
Type C: Programming Practice/Knowledge based Questions
Question 1
Write a program to count the number of times a character occurs in the given string.

Solution
str = input("Enter the string: ")
ch = input("Enter the character to count: ");
c = str.count(ch)
print(ch, "occurs", c, "times")
Output
Enter the string: KnowledgeBoat
Enter the character to count: e
e occurs 2 times
Question 2
Write a program which replaces all vowels in the string with '*'.

Solution
str = input("Enter the string: ")
newStr = ""
for ch in str : 
    lch = ch.lower()
    if lch == 'a' \
       or lch == 'e' \
       or lch == 'i' \
       or lch == 'o' \
       or lch == 'u' :
        newStr += '*'
    else :
        newStr += ch
print(newStr)
Output
Enter the string: Computer Studies
C*mp*t*r St*d**s
Question 3
Write a program which reverses a string and stores the reversed string in a new string.

Solution
str = input("Enter the string: ")
newStr = ""
for ch in str :
    newStr = ch + newStr
print(newStr)
Output
Enter the string: computer studies
seiduts retupmoc
Question 4
Write a program that prompts for a phone number of 10 digits and two dashes, with dashes after the area code and the next three numbers. For example, 017-555-1212 is a legal input. Display if the phone number entered is valid format or not and display if the phone number is valid or not (i.e., contains just the digits and dash at specific places.)

Solution
phNo = input("Enter the phone number: ")
length = len(phNo)
if length == 12 \
    and phNo[3] == "-" \
    and phNo[7] == "-" \
    and phNo[:3].isdigit() \
    and phNo[4:7].isdigit() \
    and phNo[8:].isdigit() :
    print("Valid Phone Number")
else :
    print("Invalid Phone Number")
Output
Enter the phone number: 017-555-1212
Valid Phone Number

=====================================

Enter the phone number: 017-5A5-1212
Invalid Phone Number
Question 5
Write a program that should do the following :

prompt the user for a string
extract all the digits from the string
If there are digits:
sum the collected digits together
print out the original string, the digits, the sum of the digits
If there are no digits:
print the original string and a message "has no digits"
Sample

given the input : abc123
prints abc123 has the digits 123 which sum to 6
given the input : abcd
prints abcd has no digits
Solution
str = input("Enter the string: ")
sum = 0
digitStr = ''
for ch in str :
    if ch.isdigit() :
        digitStr += ch
        sum += int(ch)
if not digitStr :
    print(str, "has no digits")
else :
    print(str, "has the digits", digitStr, "which sum to", sum)
Output
Enter the string: abc123
abc123 has the digits 123 which sum to 6

=====================================

Enter the string: KnowledgeBoat
KnowledgeBoat has no digits
Question 6
Write a program that should prompt the user to type some sentence(s) followed by "enter". It should then print the original sentence(s) and the following statistics relating to the sentence(s) :

Number of words
Number of characters (including white-space and punctuation)
Percentage of characters that are alphanumeric
Hints

Assume any consecutive sequence of non-blank characters is a word.
Solution
str = input("Enter a few sentences: ")
length = len(str)
spaceCount = 0
alnumCount = 0

for ch in str :
    if ch.isspace() :
        spaceCount += 1
    elif ch.isalnum() :
        alnumCount += 1

alnumPercent = alnumCount / length * 100

print("Original Sentences:")
print(str)

print("Number of words =", (spaceCount + 1))
print("Number of characters =", (length + 1))
print("Alphanumeric Percentage =", alnumPercent)