Python for Kids Book: Project 8

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 8 (Silly Sentences)

Project 8 is a short project which teaches you about (old style) formatting strings. Formatting strings allow you to create a sentence template into which you can substitute words.  Four words are chosen from four lists (at random) and substituted into a sentence. The random matchings make nonsense sentences. The substitutions can be streamlined by using a data type called the tuple, so that data type is introduced and discussed. You learn how to unpack tuples and how to use a tuple to receive multiple values from a function.  The project also relies on the random.choice method.

Python for Kids Book: Project 7

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 7

Project 7 (Cryptopy) introduces dictionaries as a means of encoding text using a Caesar cipher. Along the way, you are introduced to the string module and the characters in string.printable. There is some discussion about escape sequences and examples of \n and \t are given. Since you don’t want to encrypt escape sequences the slicing operator is introduced in order to take string.printable and slice off the control characters. This becomes the character set that will be encoded.

An encryption dictionary is created and each of the characters in a test message are encrypted then joined using the join method of the empty string.  I explain why this is better than adding one character after another to an existing string.  I create a matching decryption function and decryption dictionary and test the round trip (plaintext-> ciphertext -> plaintext).

The project introduces file operations by reading a message from a file then writing the encrypted (or decrypted) message to another file.  This is first done with the base file operations open and close, then the with keyword is introduced to make the housekeeping a little easier.

I demonstrate how to use your newly written encryption functions from the command line by importing the code from your own file – your own third party module!  In order for this to work seamlessly you are introduced to the __name__ attribute and the if __name__ == “__main__”: construction.

Python for Kids Book: Project 6

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 6

Project 6 introduces the concept of objects and lists to create a program that converts text into hacker speak (ie text with numbers substituted for letters). The project revisits the creation of a simple my_message variable then shows, using the dir builtin, that the variable has a variety of characteristics (that is, attributes) other than its value. It shows that one of the attributes, upper, is like a function and calls the functions of an object methods. It shows how to call a method or access an attribute through the dot notation.

In order to implement the hacker speak project, the program must perform a number of substitutions. To do that, it uses a list. The project discusses how to make a list,  how to add elements to a list, how to iterate through a list and how to test whether something is in a list.  It highlights a ‘gotcha’ with list methods – some of them modify the list in place without returning a value.

The code includes a logical error in the manner in which substitutions are made. A print statement is used to debug and identify the location of the error before it is fixed.

The project also gives a short introduction to IDLE’s debugger. There is a problem with IDLE’s debugger on Macs (there is no right click to set a breakpoint. Command-click works for some people, but not all), so if you’re running a Mac and command-click doesn’t work for you, you might have to skip this bit.

Improvements:
Page 150 does not use the print syntax from Python 3 like I said I would. It should be:

>>> for i in dir(my_message):
          print(i)
__add__
__class__
__contains__
[...]          

Page 164 does not use the print syntax from Python 3 like I said I would. Should be:

>>> substitutions = [['a','4'], ['e','3'], ['l','1'], ['o','0'], 
                     ['t','7']]
>>> for s in substitutions:
          print s
          
['a',  '4']
['e',  '3']
['l',  '1']
['o',  '0']
['t',  '7']

Python for Kids Book: Project 5

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 5

Project 5 introduces functions by revisiting the Guessing Game from Project 3 and recasting it using a function.  The project covers the def keyword, calling a function, the fact that a function must be defined before it can be called. The project also covers how to communicate with a function (both sending information to it by passing parameters and getting information from it, using the return keyword). In order to define a function, you need to give it a name, so the project sets out naming rules for functions. You should also be documenting your code, so the project introduces docstrings, how to create them, what to put in them and how to use them.

The project illustrates a logical problem in the code an explains what a local variable is. It introduces the concept of constants defined in the body of a program that can be accessed by code within a function.  A function which conducts the game round is put inside a while loop. The user interface is changed to allow the user to exit the loop.  This involves creating a quit function which first checks with the user to confirm that they want to quit, then using the break keyword to break out of the loop to quit, or the continue keyword if the user aborts the quit. The sys module is introduced in order to use sys.exit.

Improvements:

The name of the project is actually “A More Functional Guessing Game” – named as such since it will be using a function to make the guessing game work better, but some editor somewhere had a humor transplant and changed that title.

The callout on Figure 5-4 should read “The right place for an argument.”  They completely ruined that pun <sigh>

The code at the bottom of page 133 should read:

QUIT = -1
QUIT_TEXT = 'q'
QUIT_MESSAGE = 'Thank you for playing'

That is, an additional constant QUIT_MESSAGE = ‘Thank you for playing’ should be at the bottom of the page.

The line avg = str(total_guesses/float(total_rounds)) in step 4 on page 135 should be 4 lines down – being the first line in the else: block. Otherwise the logic does not work properly when you quit in the first round. The corrected code reads:

    # new if condition (and code block) to test against quit
    if this_round == QUIT:
        total_rounds = total_rounds - 1
        # removed line from here
        if total_rounds == 0:
            stats_message = 'You completed no rounds. '+\
                              'Please try again later.'
        else:
            avg = str(total_guesses/float(total_rounds)) # to here
            stats_message = 'You played ' + str(total_rounds) +\
                              ' rounds, with an average of '+\
                              str(avg)
        break

This same correction needs to be made to the “Complete Code” on page 138.

Python for Kids Book: Project 4

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 4

Project 4 introduces the integrated development environment, IDLE, that comes prepackaged with Python. In Project 4 you learn your way around the IDLE Shell and Editor Windows. I demonstrate syntax highlighting, tab completion and editor history (making your coding life easier), how to save a file, open a file and run a file from the Editor window . You also learn how to automatically indent and de-indent your code. This makes working with code blocks much easier!

The coding concepts in this project relate to adding comments to your files – how and where to do it and some tips on adding comments so they are useful in the future. I also show you how to use comments in debugging to skip over “comment out” sections of code.

Python for Kids Book: Project 3

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 3

Project 3 explores a guessing game from the command line. In order to get a guessing game up and running you need to know how to receive input from the user. This project introduces the raw_input() builtin to accommodate this.

In order to tell whether a guess is correct, the computer must compare the guess to an answer – using the == operator. Further, since raw_input returns a string, I explain that strings and numbers are different and introduce the int() builtin in order to be able to compare the input with a number.

To give a player feedback, you need to determine whether the guess was higher or lower than the desired number. The operators > and < are introduced to address this. The if conditional along with the variants elif and else are introduced to be able to structure the feedback given to a player.

To choose a number at random you learn about import, the random module and random.randint.

The while structure introduced in Project 2 is used to allow the player to make repeated guesses of the answer. This is coupled with the break keyword to exit the loop one the correct number is guessed.

In the course of introducing the ==, > and < operators, I also give an overview of more common operators used in Python (at Table 3-1).  After introducing the operators I discuss why division in Python is a special case, how to recognize problems with division and how to get a decimal answer if that’s what you’re after.

Python for Kids Book: Project 2

In these posts I outline the contents of each project in my book Python For Kids For Dummies.  If you have questions or comments about the project listed in the title post them here. Any improvements will also be listed here.

What’s in Project 2

Project 2 is a Hello World project that covers some important basics, including what literals are, how you name a literal in order to store it (ie variables). It shows the different ways to make a string literal.If you’re going to name a value you need to know about Python’s naming rules (and PEP8 naming conventions – yah but I don’t actually mention PEP8). Those naming rules themselves rely on you not using a keyword as a name, so you also get a list of Python keywords in this project.

It also covers Python’s print statement, looping with while (including the notion of a conditional and a code block). looping with for and counting with range. By the end of the Project you can fill the screen with “Hello World!”.  To do so you repeat something 300 times. I introduce the concept of magic numbers and explain why they should be avoided. I offer the use of variables in ALL_CAPS to use as constants.

Update March 2016: The book is designed to teach you Python 2.7. However, Python 3 is on the way, and if you’d like to see what’d be different in this project if you use Python 3 see this post.

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