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Lição 2. Conditions
Dificuldade:
Tarefa«Compra na internet»
💻 Python
Você cria um programa para o caixa da loja online Cosmos. A loja tem ofertas especiais para os compradores.
Regras da promoção:
Sua tarefa — Escreva um programa que solicite ao usuário o valor da compra e o dia da semana. O programa deve calcular o custo final levando em consideração o possível desconto e determinar se a entrega será paga ou gratuita.
Formato de entrada
Primeira linha: o valor da compra (número do material).
Segunda linha: dia da semana (linha).
Formato de saída
Primeira linha: O valor final, considerando o desconto (linha).
Segunda linha: informações de entrega.
Exemplo
Entrada
6000
Sábado
Saída
Valor final: 5100.00 rublos
Entrega: gratuita
Dica
Nested conditions
You can nest some conditional statements (if) into others to create more complex and multi-level checks. This is useful when the next action depends on several consecutive conditions.
The key point here is the correct indentation (usually 4 spaces), which shows Python which block of code belongs to which condition.
Example:
x = 10
if x > 5:
print("First check passed: x is greater than 5.")
if x < 20:
print("Second check passed: x is also less than 20.")
else:
print("Second check failed: x is at least 20.")
else:
print("First check failed: x is less than or equal to 5.")
A useful tip: Try not to create too many nesting levels (3 or more). Deeply embedded code becomes difficult to read and understand. Often, complex nesting can be simplified by using logical operators.
Logical operators
Logical operators in Python are used to combine two or more conditions. They allow you to build complex logic without putting conditions into each other. The main logical operators are and, or and not.
| The | Name | Description |
|---|---|---|
or |
logical "OR" | Returns True if at least one condition is true. |
and |
logical "And" | Returns True only if both conditions are true. |
not |
logical "NOT" (negation) | Inverts the result: True becomes False and vice versa. |
Examples:
a = 5
b = 7
# and: both conditions must be true
s1 = a > 3 and b < 10 # True and True -> True
# or: at least one condition must be true
s2 = a != 5 or b >= 7 # False or True -> True
# not: inverts the result
s3 = not (a < b) # not (True) -> False
When using and, the result will be true only if both operands are true. When using or, it is sufficient for at least one of the operands to be true. The not operator turns a lie into the truth and vice versa.
Analysis of a complex example:
a, b, c = 7, 10, 11
# Original expression:
print(not(a > 7 and b <= 10) or c != 17)
# Let's take it step by step:
# 1. a > 7 -> 7 > 7 -> False
# 2. b <= 10 -> 10 <= 10 -> True
# 3. (False and True) -> False
# 4. not(False) -> True
# 5. c != 17 -> 11 != 17 -> True
# 6. True or True -> True
# Result: True
A useful tip: To improve readability and avoid errors in complex expressions, always use parentheses () to explicitly specify the order of calculations, even if you remember the precedence of operators (not has the highest priority, then and, then or).
The ternary operator
The ternary operator is a compact way to write a simple if-else condition that returns a value. It allows you to assign a variable a value depending on the condition, and all this in one line.
Syntax: [value if true] if [condition] else [value if false]
Examples:
x = 10
# If x > 5, result will be 100, otherwise 200
result = 100 if x > 5 else 200
print(result) # Will output: 100
y = 20
# Assign the larger of the two values to the variable z
z = x if x > y else y
print(z) # Outputs: 20
# Assign a text value
result_text = "positive" if x > 0 else "non-positive"
print(result_text) # Outputs: positive
A useful tip: The ternary operator is great for simple assignments. However, if the logic becomes more complicated or if, depending on the condition, you need to perform different actions (rather than just return a value), it is better to use a full-fledged if-else construct to preserve the readability of the code.
One-line conditions
If the condition body (if, elif, or else) consists of only one instruction, Python allows you to write it in the same line after the colon.
Example:
x = 10
if x > 5: print("x is greater than 5")
Important style note: Although this notation is syntactically correct, it is often not recommended by the Python Code Style Guide (PEP 8). Placing instructions on a separate line with indentation improves readability and is a generally accepted standard. Use a one-line entry with care, mostly for very simple and obvious actions.
main.py
Teste 1
Teste 2
Teste 3
Teste 4
Teste 5
Teste 6
Teste 7
Teste 8
Teste 9
Teste 10
Solução do desenvolvedor
# Запрашиваем у пользователя сумму покупки и преобразуем ее в вещественное число
purchase_amount = float(input())
# Запрашиваем у пользователя день недели и приводим его к нижнему регистру для удобства сравнения
day_of_week = input().lower()
# Создаем переменную для итоговой суммы, изначально она равна сумме покупки
final_amount = purchase_amount
# Проверяем первое условие: сумма покупки больше 5000
if purchase_amount > 5000:
# Если условие истинно, рассчитываем скидку 15% и вычитаем ее из итоговой суммы
final_amount = purchase_amount * 0.85 # 100% - 15% = 85%
# Проверяем второе условие: день недели - суббота или воскресенье
if day_of_week == "суббота" or day_of_week == "воскресенье":
# Если условие истинно, доставка бесплатная
delivery_info = "Доставка: бесплатно"
else:
# Если условие ложно (любой другой день), доставка платная
delivery_info = "Доставка: платная"
# Выводим итоговую сумму, отформатированную до двух знаков после запятой
print(f"Итоговая сумма: {final_amount:.2f} руб.")
# Выводим информацию о доставке
print(delivery_info)
