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你出色地完成了任务！这是一个不小的挑战，但你找到了正确答案。你离编程大师又近了一步！继续保持，每一步都让你更强大。
课程 3. FOR cycle
难度：
任务«节日购物»
💻 Python
你计划举办一场节日晚宴，但预算非常有限。你的任务是编写一个辅助程序，实时追踪你的花费。
程序首先需要询问你的总预算以及你打算购买的商品数量。然后，对于每件商品，程序应请求输入其名称和价格。
每添加一件商品后，程序必须显示已添加的商品以及你还剩余多少钱。如果在某个时刻你的支出超过了预算，程序应立即显示警告，但仍继续将商品添加到列表中。
当你输入完所有商品的信息后，程序必须显示总花费金额以及你账户中的最终余额（可能为负数）。
输入格式
第一行：预算（整数）。
第二行：商品数量（整数）。
接下来是每种商品对应的两行：
- 商品名称（一行）。
- 商品价格（整数）。
输出格式
对于每个输入的商品：
- 显示商品名称和预算余额（一行）。
- 如果超出预算，则额外显示一条警告（一行）。
输入所有商品后：
- 最终报告，包含总支出金额和最终余额（多行）。
示例
输入
1500
3
拿破仑蛋糕
800
香槟
500
蜡烛
150
输出
已添加商品：拿破仑蛋糕。预算剩余：700
已添加商品：香槟。预算剩余：200
已添加商品：蜡烛。预算剩余：50
购买已完成。
总花费：1450
最终余额：50
提示
Basics of the forcycle
The for loop in Python is your main tool for iterating through elements in any sequence. Imagine that you have a box with different items. The for loop allows you to take one item at a time, do something with it, and move on to the next until the items in the box run out.
It is used to iterate over sequences such as lists, strings, tuples, sets, or even keys in a dictionary. The same block of code is executed for each element of the sequence.
Syntax:
for element in sequence:
# a block of code that will be executed for each element
# IMPORTANT: this block must be indented!
Here, the element is a temporary variable that is assigned a different value from the sequence at each iteration. You can name this variable any way you want, but it's better to choose a meaningful name (for example, fruit for a list of fruits or letter for a string).
Iterating through the list
A list is an ordered collection of items. The for loop will run through it from the first element to the last.
fruits = ['apple', 'banana', 'cherry']
for fruit in fruit:
print(fruit)
Conclusion:
apple
banana
cherry
Iterating over the line
A string is, in fact, a sequence of characters. Therefore, the for loop can iterate over it just as easily.
word = "Python"
for a letter in a word:
print(letter)
Conclusion:
P
y
t
h
o
n
Cycle control: break and continue
Sometimes you don't have to go through the whole cycle to the end. There are special operators for this.
The break operator
The break operator is used to immediately and completely terminate the loop. As soon as the program encounters a break, it immediately exits the loop and continues execution from the next line of code after it.
A useful tip: break is indispensable when you are looking for something. Once you've found what you're looking for, there's no point in continuing the search.
Example: We have a list of numbers, and we want to find the first even number and stop the loop as soon as it is found.
numbers = [1, 3, 5, 6, 7, 9, 10]
for num in numbers:
if num % 2 == 0: # Check for parity
print(f"The first even number is found: {num}")
break # Immediately exit the loop
print("The loop is completed.")
Conclusion:
The first even number was found: 6
The cycle is completed.
Please note that the numbers 7, 9, and 10 were not checked, as the cycle was interrupted by the number 6.
The continue operator
The continue operator is used to skip the current iteration and immediately move on to the next one. All the code that is in the loop after continue will not be executed for the current element.
A useful tip: continue is very convenient for "filtering" data inside a loop. If the current item doesn't suit you by some criterion, you just skip it and move on to the next one.
Example: We have a list of numbers, and we want to output all the numbers except the even ones.
numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
for num in numbers:
if num % 2 == 0: # Check for parity
continue # If the number is even, skip print() and go to the next number.
print(num)
Conclusion:
1
3
5
7
9
When num was equal to 2, 4, 6, etc., the if condition was met, continue skipped the print(num) command, and the loop immediately started a new iteration.
The difference between break and continue is in a nutshell
break: "Stop, car!". Stops the cycle completely.continue: "This one doesn't fit, let's do the next one!". Skips only the current step.
The else block in the for
loop
The for loop may have an optional else block. This block is executed only if the loop has completed all its iterations naturally, that is, it has not been interrupted by the break operator.
A useful tip: It is a very powerful tool for search tasks. The else block makes it easy to handle a situation where the search has ended but nothing has been found.
Example 1: The loop ended normally
for number in range(3):
print(number)
else:
print("The cycle is completed without interruptions.")
Conclusion:
0
1
2
The cycle is completed without interruptions.
Example 2: The loop is interrupted by the break
for number in range(3):
if number == 1:
print("We found 1, we break the loop.")
break
print(number)
else:
# This block will not be executed because there was a break
print("The cycle is completed without interruptions.")
Conclusion:
0
We found 1, we interrupt the cycle.
Practical examples
The sum of all the numbers in the list
This is a classic task for understanding how to work with a cycle and accumulate results.
numbers = [1, 2, 3, 4, 5]
amount = 0 # Initialize the variable to store the amount BEFORE the loop
for a number in numbers:
sum += number # At each iteration, we add the current number to the total
print(f' Sum: {sum}') # Output the final result AFTER the loop
Conclusion: Amount: 15
A useful tip: Although this method perfectly demonstrates how the loop works, in real code it is better to use the built-in sum() function to find the sum of the list elements: print(sum(numbers)). It's shorter and more efficient.
Finding the maximum number in the list
Here we assume that the first element is the maximum, and then in the loop we compare it with all the others.
numbers = [1, 7, 3, 9, 5]
maximum = numbers[0] # We take the first element as the temporary maximum
for a number in numbers:
if the number is > maximum: # If we find a number greater than our maximum...
maximum = number # ...then we update the maximum
print(f' Maximum: {maximum}')
Conclusion: Maximum: 9
A useful tip: As with the sum, Python has a built-in function max() for this task: print(max(numbers)). Knowing these functions saves time, but understanding how they work using the for loop is a key skill for a programmer.
main.py
测试 1
测试 2
测试 3
测试 4
测试 5
测试 6
测试 7
测试 8
测试 9
测试 10
开发者解答
# Запрашиваем и считываем общий бюджет, преобразуя его в целое число
budget = int(input())
# Запрашиваем и считываем количество товаров, преобразуя его в целое число
num_items = int(input())
# Создаем переменную для хранения общей суммы потраченных средств, изначально она равна 0
total_spent = 0
remaining_budget = budget
# Запускаем цикл, который повторится столько раз, сколько товаров мы планируем купить
for i in range(num_items):
# Внутри цикла запрашиваем название очередного товара
item_name = input()
# Затем запрашиваем его цену и преобразуем в целое число
item_price = int(input())
# Добавляем цену текущего товара к общей сумме трат
total_spent = total_spent + item_price
# Вычисляем, сколько денег осталось от первоначального бюджета
remaining_budget = budget - total_spent
# Выводим сообщение о том, какой товар добавлен и какой остаток бюджета
print(f"Добавлен товар: {item_name}. Остаток бюджета: {remaining_budget}")
# Проверяем условие: если остаток бюджета стал меньше нуля...
if remaining_budget < 0:
# ...то выводим предупреждение с указанием суммы превышения
# Мы используем -remaining_budget, чтобы показать положительное число долга
print(f"Внимание! Бюджет превышен на {-remaining_budget}.")
# После завершения цикла выводим пустую строку для лучшей читаемости
print("\nПокупки завершены.")
# Выводим итоговую сумму всех трат
print(f"Всего потрачено: {total_spent}")
# Выводим финальный остаток, который может быть положительным или отрицательным
print(f"Итоговый остаток: {remaining_budget}")
