2nd Homework

Download hw_2.tar.gz and extract it. Then add your homework solutions in the contained directory. Rename the directory according to the rules in the syllabus before submitting it as compressed archive.

  1. Numeric computation
    Write a program that asks for the radius of a sphere and prints its surface and volume (rounded to 3 digits).
    A sample run of this program:
    Enter the radius: 3.4
    The sphere has a surface of 145.267
    The volume of the sphere is 164.636
    
    Name the program file: sphere.py
  2. Fix the program below
    There are a few bugs in the code below. The code should calculate the two solutions to quadratic equations like $ax^2+bx+c=0$. One issue is that the code was written for Python 2, but there are more problems... [hint: the main bugs are conceptual errors - those are particularly evil, b/c the compiler/ interpreter cannot find them] The results should be rounded to three digits.
    from math import sqrt
    a = input("a: ")
    b = input("b: ")
    c = input("c: ")
    q = sqrt(b**2 - 4 * a * c)
    x1 = (-b + q) / 2*a
    x2 = (-b - q) / 2*a
    print x1, x2
    
    Name the program file: quadratic_equation.py
  3. Even numbers
    Print all even numbers starting with 0 up to a value supplied by the user.
    A sample run of this program:
    Upper limit: 7
    0
    2
    4
    6
    
    Name the program file: even.py
  4. Calculating a sum Write a program that adds up all odd numbers between 1 and a user-defined upper limit. However, only numbers that can be divided by 3 without a remainder should be added. The upper limit has to be integral and must be included in the sum. [hint: one way to solve this is to read about the modulo operator in the documentation; however, if you use pencil and paper to really understand the problem, there is an easier solution available]
    A sample run of this program:
    Upper limit: 71
    Sum: 432
    
    Name the program file: odd_sum.py
  5. Simple search Write a program that asks the user for two strings. The first string is a comma-separated list of relative filenames. The program should then count the non-overlapping occurrences of the second string in all the given files. The comparison must not be case sensitive.
    A sample run of this program:
    Files: f1.txt,f2.txt
    Needle: lorem
    Occurrences: 12
    
    Name the program file: search.py
  6. Downloading data Write a script that downloads a file from the internet. The file contains a fictitious weather forecast for the next seven days. Once you can access the file's content, calculate the average temperature for the next weekend (Saturday and Sunday). Based on this average, the program should then suggest an activity for the weekend.
    >25 C
    swimming
    >12 - 25 C
    hiking
    >5 - 12 C
    watching movies
    >-5 - 5 C
    relaxing in the local hot springs
    ≤-5 C
    skiing
    The fictitious weather forecast is available at http://find-santa.eu/teaching/cms/data/fc.txt
    A sample run of this program:
    Next weekend, hiking would be a good activity.
    
    Name the program file: downloading.py
  7. VRPTW instances
    The vehicle routing problem with time windows is a well known combinatorial optimization problem. There are many heuristics and local search methods available that help obtaining good results. However, before any instance can be solved, the input files have to be read.
    Develop a small Python script that downloads the file r101.txt and then reads it line by line (using a for loop). Doing so, print the sum of the demand of all entries. [hint: ''.split(.) is your friend]
    A sample run of this program:
    Total demand: 1458.0
    
    Name the program file: print_demand.py
  8. Financial Data
    Using your favorite web browser, go to http://www.google.com/finance and search for a company of your choice. Then click on "Historical prices" and select a date range which provides at least 50 values. Click on "Download to spreadsheet" to obtain the data in the CSV format.
    Write a Python script that reads each data line's closing price. The script then needs to calculate the average closing price over the entire period. Print the average closing price (two digits after the decimal point) and indicate whether it is higher or lower than the most recent closing price.
    A sample run of this program:
    File to analyze: ${YOURFILE}
    The average closing price was ${AVERAGE_CLOSING_PRICE}.
    The most recent closing price (...) was ... above the average.
    
    [Output depends on the file you downloaded... to allow the grader to work on your computer, download the data for Andritz AG.]
    Name the program file: financial_data.py
  9. Factoring of integers
    Write a program that prints out all the factors of a given number.
    A sample run of this program:
    Integer: 30
    30 = 2 * 3 * 5
    
    Name the program file: factor.py
  10. ROT13 (hard!)
    ROT13 is a simple substitution cipher. Read about it at http://en.wikipedia.org/wiki/Rot13. It is built on the fact that each character has an integer ordinal (i = ord(c); c = chr(i)).
    Read an entire file into a single string and convert it to uppercase (for simplicity). Then encrypt/ decrypt the text using ROT13. To translate the text, iterate over all characters in the string. Characters other than A-Z should not be changed. Test your code with the provided rot13.txt file. Besides asking the user for an input filename, the only output of the program must be the decoded content of the file. [note: you are not allowed to use Python's translate function or dictionaries; A has the ordinal 65, Z has the ordinal 90]
    A sample run of this program:
    File to decode: rot13.txt
    [Patient, little bird - start working on this task...*]
    
    * this is not the actual output as it would be a spoiler to know the result before even starting to try to figure out the solution yourself ;)
    Name the program file: rot13.py