Lab: File Data and Collections

Note

Source: Adapted from the C# edition (dictionaries/lab-filedata.rst). The C# lab uses StreamReader and Dictionary<string,string>; this Python version uses open() / with and Python dict.

Goals for this lab:

• Read data from a text file into a dictionary.

• Query and report on the data using dictionary operations.

• Practice combining file I/O, loops, and collections.

Overview

You will write a program that reads a simple data file and answers queries about its contents. The file grades.txt has one record per line in the format name:score:

Alice:91
Bob:78
Carol:85
David:92
Eve:67

Steps

1. Read the file into a dictionary

   Write a function read_grades(filename) that opens filename, reads each line, splits on :, and returns a dict mapping each student name (string) to their score (integer).

   def read_grades(filename):
       grades = {}
       with open(filename) as f:
           for line in f:
               name, score = line.strip().split(":")
               grades[name] = int(score)
       return grades
   

2. Query the dictionary

   Using read_grades, write a main program that:

   1. Prints the score for a user-supplied name (or a “not found” message).

   2. Prints the name and score of the student with the highest score.

   3. Prints the class average, rounded to one decimal place.

   4. Prints all students whose score is below a threshold entered by the user.

3. Create the data file

   Create grades.txt with at least five records in the name:score format shown above. Test your program with this file.

4. Word frequency from a file

   Write a second program that reads any plain-text file, counts the frequency of each word (case-insensitive, punctuation stripped), and prints the 10 most common words with their counts.

   Use collections.Counter for a concise solution, but also write the manual accumulation version using a plain dict for comparison.

Extension

Modify the grade reader so the file can have blank lines and lines starting with # (comments), which should both be skipped silently. This is good defensive file-reading practice.