📌 Q&A: What Exactly Does the FileHandler Do, and Why Must PhoneBookApplication Still Add Numbers?

[Rajeev Bagra]

📌 Context Code: FileHandler and PhoneBookApplication

class FileHandler:
    def __init__(self, filename):
        self.__filename = filename

    def load_file(self):
        names = {}
        with open(self.__filename) as f:
            for line in f:
                parts = line.strip().split(';')
                name, *numbers = parts
                names[name] = numbers
        return names


class PhoneBookApplication:
    def __init__(self):
        self.__phonebook = PhoneBook()
        self.__filehandler = FileHandler("phonebook.txt")

        # add the names and numbers from the file to the phone book
        for name, numbers in self.__filehandler.load_file().items():
            for number in numbers:
                self.__phonebook.add_number(name, number)

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📌 Q&A: What Exactly Does the FileHandler Do, and Why Must PhoneBookApplication Still Add Numbers?

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Q1: What is the purpose of the FileHandler class?

A:
The FileHandler class is designed solely to read the contents of a file. It takes a filename during initialization and, when the load_file() method is executed, it reads each line, splits the data, and returns a dictionary mapping each name to its list of phone numbers.

For example, if the file contains:

Eric;02-1234567;045-4356713
Emily;040-324344

The output of load_file() will be:

{
    "Eric": ["02-1234567", "045-4356713"],
    "Emily": ["040-324344"]
}

This method provides structured data but does not interact with the PhoneBook object.

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Q2: If FileHandler returns the data, why does PhoneBookApplication still need to add numbers manually?

A:
Even though FileHandler extracts and formats the data, it does not store anything inside the PhoneBook. Its job ends after returning the dictionary.

The PhoneBookApplication must therefore loop through the returned data and call:

self.__phonebook.add_number(name, number)

This is necessary because adding phone numbers to the PhoneBook is not the FileHandler’s responsibility.

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Q3: Wouldn’t it be simpler if FileHandler added the data directly to the phonebook?

A:
While it may seem convenient, it would violate a core OOP design guideline: the Single Responsibility Principle (SRP).

• FileHandler should do one job only: reading files.
• PhoneBook should do one job only: storing and managing contact data.
• PhoneBookApplication should coordinate the workflow.

If FileHandler started modifying the PhoneBook, it would no longer be reusable or cleanly designed.

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Q4: What is the role of PhoneBookApplication in this setup?

A:
PhoneBookApplication acts as the controller of the entire program. It:

1. Creates a PhoneBook object
2. Creates a FileHandler object
3. Loads the raw data from the file
4. Adds each name and phone number into the PhoneBook

This ensures that the program maintains clear boundaries between reading data, storing data, and executing the main logic.

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Q5: How do all three components work together?

A:

Component	Responsibility
FileHandler	Reads file → returns data as a dictionary
PhoneBook	Stores names and numbers; provides methods like add_number()
PhoneBookApplication	Reads data via FileHandler and inserts it into the PhoneBook

Each component does exactly one focused task, making the program easier to maintain, debug, and expand.

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If you’d like, a diagram illustrating the class interactions or a full working example with the PhoneBook class included can also be prepared for your forum audience.

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