# Learn Lambda Functions by Building an Expense Tracker - Step 36

### Tell us what’s happening:

I know what the answer is but I’m getting stuck on why the ’ is used before the "" in this case. Also, why is there a space between the : and ’ in this problem?

``````def add_expense(expenses, amount, category):
expenses.append({'amount': amount, 'category': category})

def print_expenses(expenses):
for expense in expenses:
print(f'Amount: {expense["amount"]}, Category: {expense["category"]}')

def total_expenses(expenses):
return sum(map(lambda expense: expense['amount'], expenses))

def filter_expenses_by_category(expenses, category):
return filter(lambda expense: expense['category'] == category, expenses)

def main():
expenses = []
while True:
print('\nExpense Tracker')
print('2. List all expenses')
print('3. Show total expenses')
print('4. Filter expenses by category')
print('5. Exit')

choice = input('Enter your choice: ')

if choice == '1':
amount = float(input('Enter amount: '))
category = input('Enter category: ')

# User Editable Region

elif choice == '2':
print('\nAll Expenses:')
print_expenses(expenses)
elif choice == '3':
print(f'\nTotal Expenses: ', total_expenses(expenses))

# User Editable Region

``````

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