Introduction to Programming

Lesson 10 Advanced Sequence Manipulation

AOIT Introduction to Programming

Lesson 10

Advanced Sequence Manipulation

Teacher Resources

Resource

Description

Teacher Resource 10.1

Python Programs: hangman.py and hangman_stage.py (separate ZIP file)

Teacher Resource 10.2

Presentation and Notes: Advanced Sequence Manipulation (includes separate PowerPoint file)

Teacher Resource 10.3

Rubric: Complex Programming Project

Teacher Resource 10.4

Unit Test: Independent Programming Assignment

Teacher Resource 10.5

Answer Key: Unit Test

Teacher Resource 10.6

Key Vocabulary: Advanced Sequence Manipulation

Teacher Resource 10.7

Bibliography: Advanced Sequence Manipulation

Teacher Resource 10.2

Presentation Notes: Advanced Sequence Manipulation

Before you show this presentation, use the text accompanying each slide to develop presentation notes. Writing the notes yourself enables you to approach the subject matter in a way that is comfortable to you and engaging for your students. Make this presentation as interactive as possible by stopping frequently to ask questions and encourage class discussion.

This presentation does the following:

· Reviews and categorizes the key Python methods and functions used with sequences (strings, lists, and tuples) that have already been introduced

· Introduces new string methods and functions that will be used in programming projects yet to come in this course and puts them into the correct categories

· Provides an opportunity for additional analysis and practice for the methods and functions that will be used in the minor project (Hangman program)

Presentation notes

In this presentation, you’ll learn how to use both methods and functions to make sequences more powerful. To begin, let’s review the difference between a method and a function.

Methods use object-oriented notation. For example, string.isalnum() is invoking the isalnum method of the String class. This works with "124".isalnum() because of a concept called inheritance. Because "124" is a string, it inherits all of the methods that belong to the String class. If you did this:

test='124'

test.isalnum()

It would also work, because the assignment statement set test to a string, which means that test has inherited all of the methods for the String class.

A function is not part of a class, so you don’t need to specify class in the call, which means you’re not using object-oriented notation. So, for example, len('124') is all you would need.

Presentation notes

Sequences (strings, lists, and tuples) are common constructs in Python programs. It’s the methods and functions applied to these constructs that make them powerful.

This presentation reviews and categorizes some of the methods and functions you have used in past programs, and it introduces a few new methods and functions you will be using in the Hangman program.

Presentation notes

String-testing methods test to see whether a string has a certain form, and they return True or False.

You have seen these methods before in the New Password program, where you tested the user’s proposed password to be sure it followed the password formation rules.

You will see the string.isalpha() method again in the Hangman program.

The method string.islower() tests to see whether the string is all lowercase.

Presentation notes

Case-changing methods change the case of a string. Rather than simply testing, like the string-testing methods, they operate on the string and return the changed string.

You have seen these methods before in the Menu and Vacation programs, where you changed the case of some of the text.

You will see the string.lower() method again in the Hangman program.

The method string.swapcase() swaps the case from lowercase to uppercase, or vice versa.

No method ever changes a string in place. Rather, it returns a new string derived from the old one.

Presentation notes

String formatting methods format string (or text) output, either to the Python IDLE screen or to printed output.

You have seen these methods before in the Menu program, and you might use them again in formatting the text art in Hangman.

The method to right-justify is string.rjust(width). To right-justify means to line up the string (text) with the right side of the available print space.

Presentation notes

Escape sequences are used in Python programs to print characters that have a special meaning (for example, quotation marks that are used to delimit strings) or that cannot be indicated with single keyboard characters or words (like \n to direct Python to put printed output on a new line).

Escape sequences were introduced in the Vacation and Menu programs, and they might be useful in the Hangman text art.

The escape sequence to print a single quote is \'.

Presentation notes

The most common and useful string-searching method is find(), which finds the first occurrence of a substring in a string.

The find() method is used in Hangman to check whether the letter just guessed by the user is in the mystery word. If the letter is in the word, the method will return the zero-based position of the letter. If the letter is not in the word, the method will return -1. The program branches one way or another based on the return value.

Presentation notes

In the Hangman program, you want to be sure the letter guess doesn’t have any leading or trailing blanks (that is, blanks at the beginning or the end of the string) that the player inadvertently typed in.

To ensure that this is true, you use the strip() string method to strip off the blanks (if they are there). (The strip() method doesn’t return an error if the blanks are not there; it only strips off whatever blanks happen to be there.)

"Happy Birthday! ".strip() returns this:

Happy Birthday!

This type of function is more useful than it may appear. A lot of data that is read in from files will have blank spaces at the beginning or end of the string. This can cause many problems for comparisons. The string-stripping and string-replacement methods help to easily remove the blanks.

Presentation notes

You have seen several list and tuple methods and functions recently in the Shuffle Cards program.

The append() function was used in Shuffle Cards to append each card string in turn to the end of the list of cards.

You used the pop() built-in list method to return the first card in the deck to the calling function and remove it from the list.

If you wanted to return the last card in the deck instead, you would code this:

return deck.pop()

Presentation notes

In the Hangman program, the current state of the mystery word with the player’s correct guesses inserted is constantly being printed out. For example, if the mystery word is hyena and the player has just guessed a, the player needs to get a printout of “_ _ _ _ a.” If the mystery word is cat and the player has already correctly guessed c and a, the user needs to see “c a _.”

The join() method has a format of string.join(list). In the Hangman program, in the example on this slide, the string is re-created each time the user guesses, so there is no string to join to. Therefore, the string is designated as a null string ('').

In the second example on the slide, the word (theword) is a tuple, and its length is being assigned to variable word_len.

If the mystery word is antelope, the value assigned to word_len is 8.

Presentation notes

String methods have been used extensively in prior programs. In future programs, especially the minor project (Hangman) and the culminating projects, string methods, plus list and tuple methods and functions, will play a major role.

To keep track of all these common and powerful programming constructs, it is helpful to categorize them by what they do and how they operate.

This course’s QuickStart Guide contains additional information about these methods and functions.

Presentation notes

Teacher Resource 10.3

Rubric: Complex Programming Project

Student Names: ______________________________________________Date: ________________

Exemplary

Solid

Developing

Needs Attention

Required elements

All required elements are included in the assignment. Some additional elements are included to enhance the assignment.

All required elements are included in the assignment.

One or two of the required elements are missing.

More than two required elements are missing.

Output design and results

The assignment is designed according to the best programming practices taught in the course. The program runs without errors and always produces the intended results. The output shows an excellent understanding of the intended audience.

The assignment mostly follows the best programming practices taught in the course. The program runs without significant errors and produces the intended results. The output shows a good understanding of the intended audience.

The assignment does not always follow the best programming practices taught in the course. The program runs without errors but occasionally does not produce the intended results. The output does not show a good understanding of the intended audience.

The assignment does not follow the best programming practices taught in the course. The program generally runs without errors but sometimes does not produce the intended results. The output shows little or no understanding of the intended audience.

Code design and organization

The code is clearly organized, with a logical flow of connected elements. The code follows the best programming practices taught in the course.

The code is organized, and most elements are well connected. The code mostly follows the best programming practices taught in the course.

The code is not well organized. The code does not always follow the best programming practices taught in the course.

The code is sloppy, with some serious logic errors. The code does not follow the best programming practices taught in the course.

Coding

The code is clean and obvious, with no mistakes. The program is documented with informative comments. The comments show an outstanding grasp of the technical concepts.

The code is clean, with only a few minor mistakes or problems. The program is documented with informative comments. The comments show a good grasp of the technical concepts.

The code is a little sloppy, with one serious problem and/or a number of minor mistakes or problems. The code has comments, but they might not be well understood by peer programmers.

The code is sloppy, with many serious and minor mistakes and problems. The code is not commented or is inadequately commented.

Test plan

The test plan contains a comprehensive set of test cases highly appropriate for the program objectives.

The test plan contains a minimal set of test cases appropriate for the program objectives.

The test plan contains a few test cases, most of which are appropriate for the program objectives.

The test plan does not contain enough appropriate test cases to adequately test the program.

Mechanics

There are no grammatical, spelling, or punctuation errors in the program messages or code comments.

There are few grammatical, spelling, or punctuation errors in the program messages or code comments.

There are some grammatical, spelling, or punctuation errors in the program messages or code comments.

There are many grammatical, spelling, or punctuation errors in the program messages or code comments.

Additional Comments:_____________________________________________________________________________

_____________________________________________________________________________

Teacher Resource 10.4

Unit Test: Independent Programming Assignment

Student Name: ______________________________________________________________

Date: _______________________________________________________________________

Directions: The problem statement and requirements below define your assignment for this unit test.

First answer the questions following the problem statement and requirements. Then write an algorithm to satisfy the problem statement and requirements, and a Python program to satisfy the problem statement, requirements, and your algorithm. In doing the test, be sure to follow the programming practices you have learned so far in this course.

Problem Statement and Requirements

Write a Python program that reads in an integer and calculates the sum of all the integers from 0 to the number given and prints out the sum.

Questions

Answer the questions in the spaces below.

1. A while-statement executes the statements in a loop until some condition is satisfied. If you have a variable n, write a while-statement that starts a loop that executes until n is greater than 100.

2. If you have a string variable s, which string method would you use to test if s contains only digits: isalnum() or isdigit()?

3. Write an if-statement that tests to see if the variable s has a length greater than 4.

Algorithm

In the following space, write an algorithm that satisfies the problem statement and requirements.

Python Program

In the space below, write a Python program that satisfies the problem statement, requirements, and your algorithm. Be sure to comment your program appropriately.

Teacher Resource 10.5

Answer Key: Unit Test

Problem Statement and Requirements

Write a Python program that reads in an integer and calculates the sum of all the integers from 0 to the number given and prints out the sum.

Questions

Answer the questions in the spaces below.

1. A while-statement executes the statements in a loop until some condition is satisfied. If you have a variable n, write a while-statement that starts a loop that executes until n is greater than 100.

while n <= 100:

2. If you have a string variable s, which string method would you use to test if s contains only digits: isalnum() or isdigit()?

isdigit()

3. Write an if-statement that tests to see if the variable s has a length greater than 4.

if len(s) > 4:

Algorithm

In the following space, write an algorithm that satisfies the problem statement and requirements.

Prompt the user for an integer and store the string result in a variable number.

Test to see if the number contains only digits. If it doesn’t, print an error message and exit the program.

If the number contains only digits, calculate the sum from 0 to number using a for-loop.

Print the sum of the numbers.

Python Program

In the space below, write a Python program that satisfies the problem statement, requirements, and your algorithm. Be sure to comment your program appropriately.

# read in an integer from the user

n = input ("Enter an integer: ")

# test to see if n contains only the digits 0-9

if n.isdigit():

# initialize loop variables for calculating the sum

sum = 0

number = 0

# convert n from a string to an integer

limit = int(n)

# add up the numbers from 0 to n

for i in range(0,n):

sum = sum+i

# print out the sum

print("The sum is", sum)

else:

# print an error message if n wasn't a number

print("Error,",n,"is not an integer")

Teacher Resource 10.6

Key Vocabulary: Advanced Sequence Manipulation

Terms

Definition

escape sequence

Allows you to put special characters into a string. Such a character is defined by a backslash and another character.

Examples: \t for the tab character and \n for the newline character

multiline block string

A string whose value spans multiple lines in a source file.

Teacher Resource 10.7

Bibliography: Advanced Sequence Manipulation

The following sources were used in the preparation of this lesson and may be useful for your reference or as classroom resources.

Print

Dawson, Michael. Python Programming, 2nd ed. Boston: Thompson Course Technology PTR, 2006.

Donaldson, Toby. Python, 2nd ed. Berkeley, CA: Peachpit Press, 2009.

Downey, Allen, Jeffrey Elkner, and Chris Meyers. How to Think Like a Computer Scientist: Learning with Python. Wellesley, MA: Green Tea Press, 2002.

Guzdial, Mark. Introduction to Computing and Programming in Python (A Multimedia Approach). Upper Saddle River, NJ: Pearson Education, 2005.

Hetland, Magnus Lie. Beginning Python: From Novice to Professional, 2nd ed. Berkeley, CA: Apress, 2008.

Lutz, Mark. Learning Python, 3rd ed. Sebastopol, CA: O’Reilly Media, 2008.

Miller, Bradley N., and David L. Ranum. Python: Programming in Context. Sudbury, MA: Jones and Bartlett Publishers, 2009.

Sande, Warren, and Carter Sande. Hello World!: Computer Programming for Kids and Other Beginners. Greenwich, CT: Manning Publications, 2009.

Copyright © 2009–2015 NAF. All rights reserved.

Copyright © 2009–2015 NAF. All rights reserved.