辅导python assignment online textboo、辅导python Bubble Sort algorithm

Tutorial 4

Problem 1.

Page 72, Section 8.3 of our online textbook:

Write a function that takes a string as a parameter and displays the letters backward, one per

line. Then, write another function that takes a string as a parameter and returns the string

reversed (without printing it).

Problem 2.

Consider the Bubble Sort algorithm below:

for end in range(len(data) – 1, 0, -1):

for swapIndex in range(0, end, 1):

if data[swapIndex] < data[swapIndex + 1]:

# we swap:

tempVar = data[swapIndex +1]

data[swapIndex +1] = data[swapIndex]

data[swapIndex] = tempVar

Hand trace the algorithm while we are sorting the following data list in a decreasing sort order:

4 9 6 3 1 8 2 0 5 7

As we are answering this question, let’s show our work. This is to say, what did the list looks like

before and after each iteration of the algorithm.

Problem 3.

Write a recursive function printPattern(seed, depth) such that when we call it as

follows: printPattern('a', 8), it produces the following output:

Hint: Investigate the built-in functions ord('a'), which produces 97, and chr(97) which

produces 'a'. Perhaps, we can combine them.

Why is the first parameter called ‘seed’? Why is the second parameter called ‘depth’?

Problem 4.

Exercise 8.3 from our online textbook:

A string slice can take a third index that specifies the “step size”; that is, the number of spaces between

successive characters. A step size of 2 means every other character; a step size of 3 means every third,

etc.

A step size of -1 goes through the word backwards, so the slice [ : : -1] generates a reversed string. Use

this to write a loop-free (i.e., no loop) version of the function is_palindrome( ).

Would this function take parameter(s) and if so, how many? Would this function return a value and if so,

what?

Problem 5.

Have a look at the Python program below:

variable1 = 1

variable2 = 2

def function1():

variable3 = 3

variable4 = variable3

return variable4

def function2(parameter1):

variable5 = parameter1

variable6 = 6

return variable5

def function3(parameter2, parameter3):

variable7 = parameter2

variable8 = parameter3

return variable9

# Main part of program

variable10 = function2(variable3)

print(function3(variable5, variable2))

variable1 = function1()

a. What is wrong with this program?

b. In general, what is the scope of a variable?

c. In general, what is the scope of a parameter?

d. In general, what is the relationship between variable scope and the stack frame of a

function?

e. What is the scope of each of the 10 variables in the Python program?

f. What is the scope of each of the 3 parameters in the Python program?

Problem 6. The keyword None

The list methods append( ) and insert( ) modify the list that calls these methods. For

example, the list aList is modified by the following statement:

aList.insert(2,26)

So, if aList was [1, 2, 3, 4], it then becomes [1, 2, 26, 3, 4]. Hence, we do

not need to reassign the result of these methods back to the list. This is to say that we do now

have to do the following:

alist = aList.insert(2,26)

Actually, the above statement will destroy our aList. To see why that is, execute the

following Python code fragment and see what it does:

Python Code Fragment:

aList = [1,2,3,4,5]

aList = aList.append(8)

print(aList)

List methods such as insert( ), append( ), and remove( ) modify the list that called

them, i.e., the list on the left hand side of the “.” (access operator). These methods do not

return anything (such as a list, a number, etc…). When Python functions and methods do not

return any value, None is returned. In the above Python code fragment, the aList is assigned

the value None because append( ) does not return a value. Hence, None is printed on the

computer monitor screen when the last statement, i.e., the print statement

print(aList) is executed.