Run update21, if you haven't already, to create the cs21/labs/03 directory. handin21 looks for your lab 3 assignments in the cs21/labs/03 directory, so make sure you create your python programs in there:
$ cd cs21/labs/03 $ xemacs classyear.py &
Your programs are graded on both correctness and style. Please review
the comments regarding programming style on the main page.
If you are graduating this year, you are a senior; if you graduate next year, you are a junior; etc. Write a program that asks the user for the current year and then asks the user for the year that they graduate in. In response, you tell the user their class year. Here are some sample runs of a working program:
$ python classyear.py Enter the current year: 2009 Enter your graduation year: 2010 You are a junior. $ python classyear.py Enter the current year: 2005 Enter your graduation year: 2007 You are a sophomore.Optionally, you can extend the program to print out informative messages if the user enters a value that is out of the valid range of a typical four-year college education. For example:
$ python classyear.py Enter the current year: 2009 Enter your graduation year: 2014 You are not yet in college. $ python classyear.py Enter the current year: 2009 Enter your graduation year: 2008 You already graduated.
Write a program dayOfYear.py that prompts the user for a date in mm/dd/yyyy format and prints the corresponding day of year. You can use split with a / delimiter to break the user input into a list of strings corresponding to the month, day and year. You will need to convert pieces of the list into integers to do the math.
>>> from string import * >>> dayString = "2/10/2009" >>> parts = split(dayString, "/") >>> print parts ['2', '10', '2009'] $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 2/10/2009 2/10/2009 is day number 41 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 3/1/2008 2/10/2009 is day number 61 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 3/1/2000 2/10/2009 is day number 61 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 3/1/1900 2/10/2009 is day number 60 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 3/1/2009 2/10/2009 is day number 60 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 1/1/2009 2/10/2009 is day number 1 $ python dayOfYear.py Enter a date in mm/dd/yyyy format: 1/1/2008 2/10/2009 is day number 1You do not need to check if the date the user entered is valid, though you may add this as an optional extension.
Write a program, in a file named encode.py, that asks the user to enter a phrase and a cyclic shift value, and produces an encoded string by applying the cyclic cipher method to just the alphabetic characters in the phrase. Your solution should encode ONLY upper and lower case characters in the phrase. Several hints at the end of this document help guide you towards a solution. It is highly recommended that you follow the hints and test your program incrementally.
A cyclic cipher, with a shift value of 3 will encode the character 'a' as the character 'd', the character 'b' as 'e', and so on (each character's encoding is shifted 3 characters to the right). A cyclic cipher wraps the encoding around the alphabetic characters, so that in this example, 'w' is encoded as 'z', 'x' is encoded as 'a', 'y' is encoded as 'b', and 'z' is encoded as 'c'. You can think of this as encoding where the alphabet is arranged in a circle, and the shift amount tells you how many places in one direction to move to find the encoding of any letter of the alphabet.
Here is what a few runs of your program might look like:
$ python encode.py This program encodes a phrase using a cyclic cipher Enter a phrase: Hello there, Zoe! What is happening??? Enter a shift value: 4 The encoded phrase is: Lipps xlivi, Dsi! Alex mw lettirmrk??? $ python encode.py This program encodes a phrase using a cyclic cipher Enter a phrase: Lipps xlivi, Dsi! Alex mw lettirmrk??? Enter a shift value: -4 The encoded phrase is: Hello there, Zoe! What is happening??? $ python encode.py This program encodes a phrase using a cyclic cipher Enter a phrase: yee ha!!! Enter a shift value: 1000 The encoded phrase is: kqq tm!!!Hints for solving: I'd suggest approaching this problem in the following way:
You will need to use the mod operator % to do a cyclic shift. Here is an example of a similar problem. The days of the week are cyclical. Suppose we assign the following numeric code to the days of the week:
0 Sunday 1 Monday 2 Tuesday 3 Wednesday 4 Thursday 5 Friday 6 SaturdayIf we wish to determine what day of the week is 100 days from Tuesday, we can look at the code for Tuesday (2), add 100, and mod the result by 7. Python tells us that (2+100)%7=4 meaning 100 days from Tuesday in a Thursday. Try a few more examples. This example works well because our numeric code started at 0 for Sunday incremented by one each time until Saturday. The expression x%y will always return a number in the range 0 to y-1 inclusive. Suppose we shifted our numeric code by 3 spots yielding the following:
3 Sunday 4 Monday 5 Tuesday 6 Wednesday 7 Thursday 8 Friday 9 SaturdayNow (5+100)%7=0, so using mod directly on this code doesn't even give us a valid code number for a day of the week. This mod trick only works if the code starts at 0. Effectively we are computing how far we are away from the first day of the week (Sunday). Think about this example as you try to implement your cyclic cipher. If lowercase 'a' had a numeric code of 0, the problem would be much easier. The problem is ord('a') = 97. If you first determine how far you need to shift relative to 'a', you can still use the mod trick.
Once you are satisfied with your programs, hand them in by typing handin21 at the unix prompt. You may run handin21 as many times as you like, and only the most recent submission will be recorded. This is useful if you realize after handing in some programs that you'd like to make a few more changes to them.