Python quiz questions

Three concurrent processes X, Y, and Z execute three different code segments that access and update certain shared variables. Process X executes the P operation (i.e., wait) on semaphores a, b and c; process Y executes the P operation on semaphores b, c and d; process Z executes the P operation on semaphores c, d, and a before entering the respective code segments. After completing the execution of its code segment, each process invokes the V operation (i.e., signal) on its three semaphores. All semaphores are binary semaphores initialized to one. Which one of the following represents a deadlock-free order of invoking the P operations by the processes?

1. X: P(a)P(b)P(c) Y: P(b)P(c)P(d) Z: P(c)P(d)P(a)

2. X: P(b)P(a)P(c) Y: P(b)P(c)P(d) Z: P(a)P(c)P(d)

3. X: P(b)P(a)P(c) Y: P(c)P(b)P(d) Z: P(a)P(c)P(d)

4. X: P(a)P(b)P(c) Y: P(c)P(b)P(d) Z: P(c)P(d)P(a)
    

A certain computation generates two arrays a and b such that a[i]=f(i) for 0 ≤ i < n and b[i]=g(a[i]) for 0 ≤ i < n. Suppose this computation is decomposed into two concurrent processes X and Y such that X computes the array a and Y computes the array b. The processes employ two binary semaphores R and S, both initialized to zero. The array a is shared by the two processes. The structures of the processes are shown below.

Process X:                         Process Y:
private i;                         private i;
for (i=0; i < n; i++) {            for (i=0; i < n; i++) {
   a[i] = f(i);                       EntryY(R, S);
   ExitX(R, S);                       b[i]=g(a[i]);
}                                 }

Which one of the following represents the CORRECT implementations of ExitX and EntryY?

(A)

ExitX(R, S) {
  P(R);
  V(S);
}
EntryY (R, S) {
  P(S);
  V(R);
}

(B)

ExitX(R, S) {
  V(R);
  V(S);
}
EntryY(R, S) {
  P(R);
  P(S);
}

(C)

ExitX(R, S) {
  P(S);
  V(R);
}
EntryY(R, S) {
  V(S);
  P(R);
}

(D)

ExitX(R, S) {
  V(R);
  P(S);
}
EntryY(R, S) {
  V(S);
  P(R);
}

1. A

2. B

3. C

4. D

A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution? (GATE CS 2013)
 

1. -2

2. -1

3. 1

4. 2

A shared variable x, initialized to zero, is operated on by four concurrent processes W, X, Y, Z as follows. Each of the processes W and X reads x from memory, increments by one, stores it to memory, and then terminates. Each of the processes Y and Z reads x from memory, decrements by two, stores it to memory, and then terminates. Each process before reading x invokes the P operation (i.e., wait) on a counting semaphore S and invokes the V operation (i.e., signal) on the semaphore S after storing x to memory. Semaphore S is initialized to two. What is the maximum possible value of x after all processes complete execution? (GATE CS 2013)

1. -2

2. -1

3. 1

4. 2

Three concurrent processes X, Y, and Z execute three different code segments that access and update certain shared variables. Process X executes the P operation (i.e., wait) on semaphores a, b and c; process Y executes the P operation on semaphores b, c and d; process Z executes the P operation on semaphores c, d, and a before entering the respective code segments. After completing the execution of its code segment, each process invokes the V operation (i.e., signal) on its three semaphores. All semaphores are binary semaphores initialized to one. Which one of the following represents a deadlockfree order of invoking the P operations by the processes? (GATE CS 2013).

1. X: P(a)P(b)P(c) Y:P(b)P(c)P(d) Z:P(c)P(d)P(a)

2. X: P(b)P(a)P(c) Y:P(b)P(c)P(d) Z:P(a)P(c)P(d)

3. X: P(b)P(a)P(c) Y:P(c)P(b)P(d) Z:P(a)P(c)P(d)

4. X: P(a)P(b)P(c) Y:P(c)P(b)P(d) Z:P(c)P(d)P(a)

The atomic fetch-and-set x, y instruction unconditionally sets the memory location x to 1 and fetches the old value of x in y without allowing any intervening access to the memory location x. consider the following implementation of P and V functions on a binary semaphore .

void P (binary_semaphore *s) {
  unsigned y;
  unsigned *x = &(s->value);
  do {
     fetch-and-set x, y;
  } while (y);
}
void V (binary_semaphore *s) {
  S->value = 0;
}

Which one of the following is true?

1. The implementation may not work if context switching is disabled in P.

2. Instead of using fetch-and-set, a pair of normal load/store can be used
    

3. The implementation of V is wrong

4. The code does not implement a binary semaphore

Consider the following code fragment:

if (fork() == 0)
{ a = a + 5; printf("%d,%d\n", a, &a); }
else { a = a –5; printf("%d, %d\n", a, &a); } 

Let u, v be the values printed by the parent process, and x, y be the values printed by the child process. Which one of the following is TRUE?

1. u = x + 10 and v = y

2. u = x + 10 and v != y

3. u + 10 = x and v = y

4. u + 10 = x and v != y

What does the below code intended to do?

def a(b, c, d):
   pass

1. defines a set and initializes it.

2. defines a function, which does nothing.

3. defines an empty class.

4. defines a method, which passes its parameters through.

Which function does in-place reversal of objects in a list?

1. list.pop(obj=list[-1])

2. list.remove(obj)

3. list.sort([func])

4. list.reverse()

What gets printed as the output of the below code?

x = True
y = False
z = False
if not x or y:
    print 1
elif not x or not y and z:
    print 2
elif not x or y or not y and x:
    print 3
else:
    print 4

1. 1

2. 4

3. 2

4. 3

What is the output of the following Python code?

tinytuple = (123, 'techbeamers')
print tinytuple * 2

1. (123, 'techbeamers') * 2

2. (123, 'techbeamers', 123, 'techbeamers')

3. None of the above

4. Error

What would be the result of the following expression in Python?

print 3/5

1. 0.6

2. 0

3. 6/10

4. None of the above

What is the output of the below Python code?

a = [1,2,3,None,(),[],]
print len(a)

1. 5

2. 6

3. 4

4. syntax error

If the following statement is run in Python, what will be the result?

print abc

1. =abc

2. 'abc'

3. NameError: name 'abc' is not defined

4. abc

What is the output of the following code?

def f():
	pass
print type(f())

1. <type 'function'>

2. <type 'type'>

3. <type 'NoneType'>

4. <type 'tuple'>

What is the output of following code?

list = [ 'Tech', 404, 3.03, 'Beamers', 33.3 ]
print list[1:3]

1. [ 'Tech', 404, 3.03, 'Beamers', 33.3 ]

2. [404, 3.03]

3. ['Tech', 'Beamers']

4. None of the above

If the following code is run in Python, what would be the result?

num = '5'*'5'

1. 333

2. 27

3. 9

4. TypeError: can't multiply sequence by non-int of type 'str'

Which of the following functions print the output to the console?

1. console.log

2. print

3. output

4. echo

Is the following statement correct?

There are two types of numbers in Python: integers and assigned values.

1. True

2. False

What is the output of the following code?

import re
sentence = 'Learn Python Programming'
test = re.match(r'(.*) (.*?) (.*)', sentence)
print(test.group())

1. (‘Learn’, ‘Programming’)

2. (Learn, Python, Programming)

3. Learn Python Programming

4. ‘Learn Python Programming’