12. Counting Characters

Studios are in-class activities to give you hands-on practice with new concepts. The first half is the Walkthrough, an instructor-led programming problem. The second half is for you to work on individually or in pairs in class.

These problems are not graded, and you are not obligated to finish them. Get as far as you can while in class, and use them as an opportunity to play with and solidify new concepts.


Write a GPA calculator program that takes grade data for a student and prints the resulting GPA. The output should look something like this:

Your grade (0.0-4.0): 4
# credits: 3
Enter another grade? [y/n]: y
Your grade (0.0-4.0): 4
# credits: 2
Enter another grade? [y/n]: n
Your GPA is: 4.0

We’ll need to use a while loop for the input portion of the program, and store the entered data in a list that contains dictionaries. Each item in the list should look something like:

{ 'grade': 3.0, 'credits': 3}

To calculate the GPA you’ll need the idea of a quality score. A quality score is the number of credits for the class multiplied by the point score. For example, if you get a B (3.0) in a class worth 3 credits, the quality score is 9.0. The GPA for a student is the sum of the quality scores divided by the total number of credits.

This will be written locally in a code editor, and run at the command line.

A program to take grade input and calculate a student's GPA

grades = []

continue_entry = True

# gather grade information
while continue_entry:
    grade = input("Your grade (0.0-4.0): ")
    credits = input("# credits: ")

    # store grades
    grades.append({'grade': float(grade), 'credits': int(credits)})

    user_wants_to_continue = input("Enter another grade? [y/n]: ")
    if user_wants_to_continue == 'n':
        continue_entry = False

# compute GPA
total_quality_score = 0
total_credits = 0

# calculate quality scores and total
for grade_info in grades:
    total_quality_score += (grade_info['grade'] * grade_info['credits'])
    total_credits += grade_info['credits']

gpa = total_quality_score / total_credits
print("Your GPA is:", gpa)


You should complete this studio locally on your computer, and not in this book. Within your lc101 directory create a new directory named counting-characters and write your code in this directory in a file counting.py.

To run your program, execute:

$ python counting.py

Write a program that calculates the number of times each character occurs in a string and prints these stats to the console. You could get the string as input from the user, but for the sake of simplicity, you may also hard-code the string into your program as the value of a variable. Here’s a test string, for your convenience:

Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nunc accumsan sem ut ligula scelerisque sollicitudin. Ut at sagittis augue. Praesent quis rhoncus justo. Aliquam erat volutpat. Donec sit amet suscipit metus, non lobortis massa. Vestibulum augue ex, dapibus ac suscipit vel, volutpat eget massa. Donec nec velit non ligula efficitur luctus.

For this example string, your output should look something like:

A: 1
h: 1
u: 28
b: 3
v: 4
x: 1
l: 17
r: 9
o: 15
j: 1
q: 3
P: 1
t: 29
U: 1
V: 1
m: 11
N: 1
g: 7
 : 50
n: 14
d: 4
D: 2
e: 26
p: 7
f: 2
i: 27
s: 29
L: 1
c: 17
a: 22
,: 4
.: 8

Bonus Missions

  • Create a function factors that takes in an integer n and generates a dictionary that contains the factors of all values from 1 to n. A factor is any number that evenly divides another number. For example, the factors of 6 are 1, 2, 3, and 6. Factors of 15 are 1, 3, 5, and 15. The keys of your dictionary should be an integer between 1 and n and the values should be a list of factors for that particular key.
  • Create a function reverse that takes in a dictionary and reverses it, such that all of the values become keys and all of the keys become values. Be careful: we do not wish to lose any information. Consider what to do if the original dictionary has lists of values for a particular key, or has duplicate values for some keys.