Q&A: Why This PhoneBook File Loading Code Was Incorrect?

[Rajeev Bagra]

✅ Context

You are building a PhoneBook Application in Python.

• The app stores phone numbers inside a PhoneBook class
• It reads saved contacts from a text file using a FileHandler class
• When the app starts, it should load all saved names and numbers from the file and insert them into the phonebook.

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✅ Initial Code (Correct Version)

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)

# the rest of the program...

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❓ Question

Why is this version incorrect?

for name, numbers in self.__filehandler.load_file().items():
self.__phonebook.add_number(name, numbers)

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✅ Answer (Easy Explanation)

Because numbers is not one phone number…
numbers is actually a list of multiple phone numbers.

So if your file contains:

{
"Rajeev": ["9991112222", "8887776666"],
"Amit": ["1234567890"]
}

Then:

• name = "Rajeev"
• numbers = ["9991112222", "8887776666"] ✅ (a list!)

But your method expects a single number, like:

add_number("Rajeev", "9991112222")

Not:

add_number("Rajeev", ["9991112222", "8887776666"])

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✅ What Happens If You Use the Incorrect Code?

Inside your PhoneBook class, you likely have:

self.__persons[name].append(number)

So instead of storing:

✅ Correct output:

"Rajeev": ["9991112222", "8887776666"]

You accidentally store:

❌ Wrong output:

"Rajeev": [["9991112222", "8887776666"]]

That means Python stores the entire list as one single item.

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✅ Correct Logic (Final Fix)

You must loop through the list of numbers:

for name, numbers in self.__filehandler.load_file().items():
for number in numbers:
self.__phonebook.add_number(name, number)

✅ This inserts each phone number one-by-one properly.

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ߎ Quick Summary for Beginners

✅ .items() gives you: name + list of numbers
✅ add_number() needs: name + single number
✅ So you must use a nested loop.

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