Week 3 Assignments

1. Real Legend:

The Unix system (https://en.wikipedia.org/wiki/Unix) is a legend. It sets the foundation for most of the modern-day operating systems that run on billions of devices. More importantly its design philosophy of simplicity and reusability has a massive influence on generations of programmers, in simple terms, to create a program that does one thing really well, and let it work with other programs.

The Unix system has many very famous commands which are also legends.  wc is one of them.  See https://en.wikipedia.org/wiki/Wc_(Unix).  You want to recreate the functions of wc in Python so that you can be a real legend too.

Input the name of an existing text file.  Output 3 numbers, the number of lines, the number of words (delimited by spaces), and the number of characters (including spaces and newlines).

2. Head, tail, and more

You've managed to recreate the classical Unix command wc with Python.  Dennis Ritchie and Ken Thompson send their regards.

They would like you to continue with a few more extremely useful Unix commands:

head: takes an input file name, number n, and an output file name; writes the first n lines of the input file to the output file.  If the output file name is not provided, just write to the screen.

hint: what happens if there are less than n lines in the input file?

tail: very similar to head, only that it writes the last n lines.

more: takes an input file name.  Writes the contents of the file to screen, but pause at a full screen and wait for input.  Once the ENTER key is hit, show the next full screen of file content, until the entire file is shown.

hint: how do you know how many lines is a full screen?  Make some assumptions.  If you really want to be accurate, look up shutil.get_terminal_size().
Extension: what if the program accepts 'any key' instead of ENTER for the next screen of output?  Do some research.

3. James Bond's Book:

Bond's missions get more complex and his code book gets longer.  It has reach a point that he can no longer memorise all the codes.  He decides to save them to a text file jamesbondscodebooktopsecretcantletanybodyseebecauseitsnotencrypted.txt.   The file contains many lines, each containing the plain text word followed by its code word.  Example:

    I            poop
    hungry       *&%#
    bored        78534
    irritated    buzzinga!

Adapt your work last time to load the code book from that text file.  Then you can use the code book to encrypt your message.

Week 3 Learning Summary

Week 3 subject 1: File Operations

• File means text files.  It's a giant leap forward which means you are finally free from keystrokes and can now process something much more complex and more meaningful!

• Always use the open() function to open a file before using, which returns a File object you'll need to refer to whenever you need to operate a file.

• Always use the .close() method to close the file after use.

• Read from files using:

• .read(number of characters)

• .readline()

Week 2 Assignments

 1. Not Lonely Anymore:

A second librarian, Charlie, joins you in the school library.  Charlie suggests that the book list you keep can be improved to include names of the authors.  You agree.  The two of you start to upgrade your automation to do the following:

• Input a line which contains the book name followed by the author's name.  Both are single words.

• If the book doesn't exist in your list, add it; if it does, update the author's name.

• Handle deletion by book name as it already does.

• If the input is 'search' followed by author's name, output a list of books by this author.

• At the end of the process, output the complete book list, one line per book, each containing the book name followed by the author's name. 

2. Bond, James Bond:

You live a double life.  During the day you are the lonely librarian, but when you are off and nobody sees you, you are James Bond the MI6 secret agent, the King's spy, with a license to kill.

You can't let others know the content of your communication with M, the head of MI6.  You have a secret code book which looks like this:

    I            poop
    hungry       *&%#
    bored        78534
    irritated    buzzinga!

So that a message like 'I am always hungry or bored or irritated' will be translated to 'poop am always *&%# or 78534 or buzzinga!'

Input a line of message you need to send to M.  Use the code book to translate it word by word to the secret form and output the translated line.  Repeat this process until a blank line is input.

Week 2 Learning Summary

 

Week 2 subject 1: Tuples

• Tuples are just like Lists, only they're immutable, i.e., their elements, and the numbers of elements, can't be altered.  HOWEVER, the elements are immutable doesn't mean that the elements of the elements can't be altered.  

• Example, if an element of a Tuple is a List, you can't replace the List with another, but you can alter the elements of the List.

• There are limited operations applicable to Tuples, including the len() function, and the .count() and .index() methods.

Week 2 subject 2: Dictionaries

• Dictionarys are like Lists, but their elements are pairs: Key:Value.  Keys are just like subscripts of Lists only that they can be of many other data types and other values.

• Dictionary is perfect for registers, dictionaries and anything you need to use an index to locate values.

• Use methods like .items(), .keys() and .values().  .items() returns a list of Tuples, while other two return Lists.

• You can't use arithmetic operations like + or * with a Dictionary.

• Learn how to tell if one Key exists in a Dictionary?  What about one Value?

• There's no .append().  Use assignments directly.  

• Note the difference with Lists where you can't assign value to an element that hasn't been appended yet.

•  A Dictionary can be initialised 

• Using initialisers directly like d = {1:'one', 2:'two', 3:'three},

• Using the dict() constructor like d = dict([(1, 'one'), (2, 'two'), (3, 'three)]), note the parameter of dict() is a list of tuples,

• There's a fancier while more confusing way, when Keys are simple strings: d = dict(one=1, two=2, three=3)

• Using the .fromkeys() method like d = dict.fromkeys([1,2,3], "numbers")

• As I said, keep exploring all the possibilities!

Knowledge Check