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Track Your Spending (or Habits)

Understand how to log structured input to a file.

We'll cover the following...

Let’s build a real-life Python project: a tracker!

You can use it to log spending, habits, workouts—anything you want to keep a record of.

Step 1: Simple spending logger

while True:
    item = input("Enter an item (or 'done' to finish): ")
    if item == "done":
        break
    amount = input("How much did you spend on it? ")
    with open("expenses.txt", "a") as file:
        file.write(item + ": $" + amount + "\n")  # Concatenate the strings before writing

print("All expenses saved!")
We’re asking the user for what they spent on and how much, and saving it to a file

Note: The item, ": $", amount, and "\n" are concatenated into a single string using the + operator.

This single concatenated string is then written to the file using file.write().

You just built a persistent expense logger!

Step 2: Read and display expenses

while True:
    item = input("Enter an item (or 'done' to finish): ")
    if item == "done":
        break
    amount = input("How much did you spend on it? ")
    with open("expenses.txt", "a") as file:
        file.write(item + ": $" + amount + "\n")

with open("expenses.txt", "r") as file:
    print("Here are your expenses:")
    print(file.read())
We’re reading back all past entries and showing them on screen

This displays all your logged items—even from last week!

Improve with functions

Break your code into functions for clarity:

def log_expense():
    while True:
        item = input("Enter an item (or 'done' to finish): ")
        if item == "done":
            break
        amount = input("How much did you spend on it? ")
        with open("expenses.txt", "a") as file:
            file.write(item + ": $" + amount + "\n")
    
    print("All expenses saved!")

def view_expenses():
    with open("expenses.txt", "r") as file:
        print("Here are your expenses:")
        print(file.read())

log_expense()
view_expenses()
Breaking the code into functions makes it easier to manage and reuse later