Python Revision Tour

Type B: Application Based Questions

•  

  Question 1

  Fill in the missing lines of code in the following code. The code reads in a limit amount and a list of prices and prints the largest price that is less than the limit. You can assume that all prices and the limit are positive numbers. When a price 0 is entered the program terminates and prints the largest price that is less than the limit.

  #Read the limit
  limit = float(input("Enter the limit"))
  max_price = 0
  # Read the next price
  next_price = float(input("Enter a price or 0 to stop:"))
  while next_price > 0 :
      <write your code here> 
      #Read the next price 
      <write your code here>
  if max_price > 0:
      <write your code here> 
  else :
      <write your code here>

  Answer

  #Read the limit
  limit = float(input("Enter the limit"))
  max_price = 0
  # Read the next price
  next_price = float(input("Enter a price or 0 to stop:"))
  while next_price > 0 :
      if next_price < limit and next_price > max_price:
          max_price = next_price
      #Read the next price 
      next_price = float(input("Enter a price or 0 to stop:"))
  if max_price > 0:
      print("Largest Price =", max_price) 
  else :
      print("Prices exceed limit of", limit);

  Question 2a

  Predict the output of the following code fragments:

  count = 0         
  while count < 10:
      print ("Hello")
      count += 1

  Answer

  Output

  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  Hello
  

  Question 2b

  Predict the output of the following code fragments:

  x = 10
  y = 0
  while x > y: 
     print (x, y)
     x = x - 1
     y = y + 1

  Answer

  Output

  10 0
  9 1
  8 2
  7 3
  6 4
  

  Explanation

  x	y	Output	Remarks
  10	0	10 0	1st Iteration
  9	1	10 0 9 1	2nd Iteration
  8	2	10 0 9 1 8 2	3rd Iteration
  7	3	10 0 9 1 8 2 7 3	4th Iteration
  6	4	10 0 9 1 8 2 7 3 6 4	5th Iteration

  Question 2c

  Predict the output of the following code fragments:

  keepgoing = True        
  x=100                   
  while keepgoing :       
      print (x)
      x = x - 10 
      if x < 50 :
         keepgoing = False

  Answer

  Output

  100
  90
  80
  70
  60
  50
  

  Explanation

  Inside while loop, the line x = x - 10 is decreasing x by 10 so after 5 iterations of while loop x will become 40. When x becomes 40, the condition if x < 50 becomes true so keepgoing is set to False due to which the while loop stops iterating.

  Question 2d

  Predict the output of the following code fragments:

  x = 45
  while x < 50 :
      print (x)

  Answer

  This is an endless (infinite) loop that will keep printing 45 continuously.

  As the loop control variable x is not updated inside the loop neither there is any break statement inside the loop so it becomes an infinite loop.

  Question 2e

  Predict the output of the following code fragments:

  for x in [1,2,3,4,5]:
      print (x)

  Answer

  Output

  1
  2
  3
  4
  5
  

  Explanation

  x will be assigned each of the values from the list one by one and that will get printed.

  Question 2f

  Predict the output of the following code fragments:

  for p in range(1,10):
     print (p)        

  Answer

  Output

  1
  2
  3
  4
  5
  6
  7
  8
  9
  

  Explanation

  range(1,10) will generate a sequence like this [1, 2, 3, 4, 4, 5, 6, 7, 8, 9]. p will be assigned each of the values from this sequence one by one and that will get printed.

  Question 2g

  Predict the output of the following code fragments:

  for z in range(-500, 500, 100):
      print (z)

  Answer

  Output

  -500
  -400
  -300
  -200
  -100
  0
  100
  200
  300
  400
  

  Explanation

  range(-500, 500, 100) generates a sequence of numbers from -500 to 400 with each subsequent number incrementing by 100. Each number of this sequence is assigned to z one by one and then z gets printed inside the for loop.

  Question 2h

  Predict the output of the following code fragments:

  x = 10                     
  y = 5                     
  for i in range(x-y * 2):  
      print (" % ", i)

  Answer

  This code generates No Output.

  Explanation

  The x-y * 2 in range(x-y * 2) is evaluated as below:

      x – y * 2
  ⇒ 10 – 5 * 2
  ⇒ 10 – 10 [∵ * has higher precedence than -]
  ⇒ 0

  Thus range(x-y * 2) is equivalent to range(0) which returns an empty sequence — [ ].

  Question 2i

  Predict the output of the following code fragments:

  c = 0
  for x in range(10): 
      for y in range(5):
          c += 1
  print (c)

  Answer

  Output

  50
  

  Explanation

  Outer loop executes 10 times. For each iteration of outer loop, inner loop executes 5 times. Thus, the statement c += 1 is executed 10 * 5 = 50 times. c is incremented by 1 in each execution so final value of c becomes 50.

  Question 2j

  Predict the output of the following code fragments:

  x = [1,2,3]
  counter = 0
  while counter < len(x):
      print(x[counter] * '%')
      for y in x:
          print(y * '* ')
      counter += 1

  Answer

  Output

  %
  * 
  * *
  * * *
  %%
  *
  * *
  * * *
  %%%
  *
  * *
  * * *
  

  Explanation

  In this code, the for loop is nested inside the while loop. Outer while loop runs 3 times and prints % as per the elements in x in each iteration. For each iteration of while loop, the inner for loop executes 3 times printing * as per the elements in x.

  Question 2k

  Predict the output of the following code fragments:

  for x in 'lamp':
      print(str.upper(x))

  Answer

  Output

  L
  A
  M
  P
  

  Explanation

  The for loop extracts each letter of the string ‘lamp’ one by one and place it in variable x. Inside the loop, x is converted to uppercase and printed.

  Question 2l

  Predict the output of the following code fragments:

  x = 'one'              
  y = 'two'              
  counter = 0            
  while counter < len(x):
      print(x[counter], y[counter])
      counter += 1

  Answer

  Output

  o t
  n w
  e o
  

  Explanation

  Inside the while loop, each letter of x and y is accessed one by one and printed.

  Question 2m

  Predict the output of the following code fragments:

  x = "apple, pear, peach"
  y = x.split(", ")
  for z in y :
     print(z)

  Answer

  Output

  apple
  pear
  peach
  

  Explanation

  x.split(“, “) breaks up string x into a list of strings so y becomes [‘apple’, ‘pear’, ‘peach’]. The for loop iterates over this list and prints each string one by one.

  Question 2n

  Predict the output of the following code fragments:

  x ='apple, pear, peach, grapefruit'
  y = x.split(', ')
  for z in y:
      if z < 'm':
          print(str.lower(z))
      else:
          print(str.upper(z))

  Answer

  Output

  apple
  PEAR
  PEACH
  grapefruit
  

  Explanation

  x.split(‘, ‘) breaks up string x into a list of strings so y becomes [‘apple’, ‘pear’, ‘peach’, ‘grapefruit’]. The for loop iterates over this list. apple and grapefruit are less than m (since a and g comes before m) so they are converted to lowercase and printed whereas pear and peach are converted to uppercase and printed.

  Question 3

  Find and write the output of the following python code:

  for Name in ['Jayes', 'Ramya', 'Taruna', 'Suraj'] :
      print (Name)
      if Name[0] == 'T' :
          break
      else :
          print ('Finished!')
  print ('Got it!')

  Answer

  Output

  Jayes
  Finished!
  Ramya
  Finished!
  Taruna
  Got it!
  

  Explanation

  The for loop iterates over each name in the list and prints it. If the name does not begin with the letter T, Finished! is printed after the name. If the name begins with T, break statement is executed that terminates the loop. Outside the loop, Got it! gets printed.

  Question 4(i)

  How many times will the following for loop execute and what’s the output?

  for i in range(-1, 7, -2):
      for j in range (3):
          print(1, j)

  Answer

  The loops execute 0 times and the code produces no output. range(-1, 7, -2) returns an empty sequence as there are no numbers that start at -1 and go till 6 decrementing by -2. Due to empty sequence, the loops don’t execute.

  Question 4(ii)

  How many times will the following for loop execute and what’s the output?

  for i in range(1,3,1):
      for j in range(i+1):
          print('*')

  Answer

  Loop executes for 5 times.

  Output

  *
  *
  *
  *
  *
  

  Explanation

  range(1,3,1) returns [1, 2]. For first iteration of outer loop j is in range [0, 1] so inner loop executes twice. For second iteration of outer loop j is in range [0, 1, 2] so inner loop executes 3 times. This makes the total number of loop executions as 2 + 3 = 5.

  Question 5

  Is the loop in the code below infinite? How do you know (for sure) before you run it?

  m = 3
  n = 5
  while n < 10:
      m = n - 1
      n = 2 * n - m
      print(n, m)

  Answer

  The loop is not infinite. To know this without running it we can analyze how n is changed inside the loop in the following way:

  n = 2 * n – m

  Substituting value of m from m = n – 1,

      n = 2 * n – (n – 1)
  ⇒ n = 2 * n – n + 1
  ⇒ n = 2n – n + 1
  ⇒ n = n + 1

  Therefore, inside the loop n is incremented by 1 in each iteration. Loop condition is n < 10 and initial value of n is 5. So after 5 iterations, n will become 10 and the loop will terminate.