67 — Project — a grade book

The bank in guide 61 saved a dict through a storage module, and the shop in guide 48 ran a command menu. A grade book puts both together: one dict mapping a student name to a list of grades, a gradebook.nme module that loads and saves it, and a menu with add, grade, report, and quit. statistics.mean from guide 54 turns a grade list into an average.

#Steps

1. A grade book is one dict: each student name maps to a list of grades. statistics.mean averages the list:

   from statistics import mean
   books = {"Mina": [88, 90], "Jun": [95]}
   show mean(books["Mina"])
   

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   It prints 89 — the average of 88 and 90.

2. Storage lives in a module, gradebook.nme, exporting load() and save, exactly like the bank module in guide 61. load() returns an empty dict when no file exists yet:

   # gradebook.nme — file storage for the grade book.
   
   import os
   use file latest
   
   def load():
       if os.path.exists("gradebook.json"):
           return json_load("gradebook.json")
       return {}
   
   def save(books):
       json_save("gradebook.json", books)
   

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3. The whole program. Save grade-book.nme next to gradebook.nme:

   # grade-book.nme — a JSON-persisted grade book.
   # Run: nme r grade-book
   # Type add, grade, report, or quit.
   
   from "gradebook.nme" import load, save
   from statistics import mean
   
   books = load()
   
   show "Grade book — kept in gradebook.json"
   while True:
       show "Commands: add, grade, report, quit"
       ask command, "? "
       if command == "add":
           ask name, "Name? "
           if name in books:
               show "Already added"
           else:
               books[name] = []
               save(books)
               show f"Added {name}"
       elif command == "grade":
           ask name, "Name? "
           if name in books:
               ask score_text, "Score? "
               score = int(score_text)
               books[name].append(score)
               save(books)
               show f"Added {score} for {name}"
           else:
               show "No such student"
       elif command == "report":
           ask name, "Name? "
           if name in books:
               scores = books[name]
               if len(scores) > 0:
                   show f"{name}: {mean(scores):.1f} average, {len(scores)} grades"
               else:
                   show f"{name}: no grades yet"
           else:
               show "No such student"
       elif command == "quit":
           show "Bye!"
           break
       else:
           show "Unknown command"
   

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   add checks the student is new, then creates an empty grade list and saves. grade checks the student exists, appends one score, and saves. report averages that student's grades and shows the count — or says there are none yet. Every change calls save, so the book survives between runs.

4. Run it and feed the commands through a pipe:

   printf 'add\nMina\nreport\nMina\ngrade\nMina\n90\nreport\nMina\nquit\n' | nme r grade-book
   

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   Grade book — kept in gradebook.json
   Commands: add, grade, report, quit
   ? Name? Added Mina
   Commands: add, grade, report, quit
   ? Name? Mina: no grades yet
   Commands: add, grade, report, quit
   ? Name? Score? Added 90 for Mina
   Commands: add, grade, report, quit
   ? Name? Mina: 90.0 average, 1 grades
   Commands: add, grade, report, quit
   ? Bye!
   

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   The report before any grade says no grades yet; after one grade it averages 90 with the :.1f format, showing one decimal place.

5. Look at gradebook.json — it holds the whole book:

   {"Mina": [90]}
   

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   Add a grade for Mina (grade then Mina then 100) and the file becomes {"Mina": [90, 100]} with an average of 95.0.

#Try it yourself

Add a list command that reports every student's average, or a top command that sorts the students by average with the sorted(..., key=...) trick from guide 66. Or make report print the highest grade too with max(scores).

#What you learned

• A grade book is a dict mapping a name to a list of grades, saved as JSON.
• load() / save() in gradebook.nme keep the file format in one module.
• statistics.mean(scores) turns a grade list into an average.
• Commands add, grade, report, quit drive a while True: menu.