Question

Task 3: Understanding Programs
Given the initial statements
s1 = [2,1,4,3]
s2 = [’c’,’a’,’b’]
show the result of evaluating each of the following sequence expressions:
s1 + s2 =>
3 * s1 + 2 * s2 =>
s1[1] =>
s1[1:3] =>

s1 + s2[-1] =>

Given the same initial statements as in the previous problem, show the values of s1 and s2 after executing each of the following statements. Treat each part independently (i.e., assume that and start with their original values each time).
s1.remove(2) =>
s1.sort() =>
s1.append([s2.index(’b’)]) =>
s2.pop(s1.pop(2)) =>
s2.insert(s1[0], ’d’) =>

Using python please Thanks

Answer 1

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s1 = [2,1,4,3]
s2 = [’c’,’a’,’b’]

s1 + s2 => will return [2, 1, 4, 3, 'c', 'a', 'b'] since + operator returns the union of two lists

3 * s1 + 2 * s2 => will return [2, 1, 4, 3, 2, 1, 4, 3, 2, 1, 4, 3, 'c', 'a', 'b', 'c', 'a', 'b'] since * operator takes copy of each element in the list n times as specified. So 3*s1 will return 3*[2, 1, 4, 3] = [2, 1, 4, 3, 2, 1, 4, 3, 2, 1, 4, 3] and 2 * s2 returns ['c', 'a', 'b', 'c', 'a', 'b'], and + operator returns the union of these two lists.

s1[1] => returns 1 since 1 is the element at index 1 in s1

s1[1:3] => returns [1, 4] (elements between index 1 and index 3 (exclusive))

s1 + s2[-1] => This will cause an exception since + operator is undefined for operands list and string. Here s1 is a list, and s2[-1] is a string (last element in s2), so these two operands can’t be added.

Given s1 = [2,1,4,3] and s2 = [’c’,’a’,’b’]

After calling s1.remove(2)

Value of s1 = [1, 4, 3] (2 has been removed)

Value of s2 = ['c', 'a', 'b']

Given s1 = [2,1,4,3] and s2 = [’c’,’a’,’b’]

After calling s1.sort()

Value of s1 = [1, 2, 3, 4] (sorted)

Value of s2 = ['c', 'a', 'b']

Given s1 = [2,1,4,3] and s2 = [’c’,’a’,’b’]

After calling s1.append([s2.index('b')])

Value of s1 = [2, 1, 4, 3, [2]]

Value of s2 = ['c', 'a', 'b']

Explanation: index method returns the index of an element in a list, here index of letter b in s2 is 2, this value is used to create a single element list (note the square braces surrounding s2.index(‘b’)) and this list is appended to S1

Given s1 = [2,1,4,3] and s2 = [’c’,’a’,’b’]

After calling s2.pop(s1.pop(2))

Value of s1 = [2, 1, 3]

Value of s2 = ['c', 'a', 'b']

The above statement will raise an exception.

Explanation. pop method removes an element from an index and return it. So s1.pop(2) will remove the element at index 2 in s1, which is 4 and pass it to the outer pop method (s2.pop(4)) but since 4 is not a valid index in s2, exception is occurred.

Given s1 = [2,1,4,3] and s2 = [’c’,’a’,’b’]

After calling s2.insert(s1[0], 'd')

Value of s1 = [2, 1, 4, 3]

Value of s2 = ['c', 'a', 'd', 'b']

Explanation: insert method adds an element (second parameter) to a specified index (first parameter). So s2.insert(s1[0], ‘d’) will insert ‘d’ into s2 at index s1[0] which is 2, remaining elements will be shifted right one place.