THEORY AND PRACTICE

Input and Output Data

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Conditions

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Занятие 2. Conditions

Difficulty level:

Task«Castle protection»

you & mdash; The main guard of the old castle. The castle has a modern security system. The rules of its operation are simple: the alarm is turned on if two conditions are met at the same time:

rn
night came. rn
at least one of the sensors worked: the movement sensor recorded the activity or the door sensor showed that they are open. Style = "Font-Size: 14pt;"> During the day, the system does not respond to sensors so as not to interfere with residents and guests of the castle.

rn

Input format

the time of the day (line: 'night' or 'day')
the state of the motion sensor (line: 'eat' or no ')
The condition of the doors sensor (line: 'open' or 'closed')

Output format

The state of the alarm (line: 'anxiety!' or 'everything is calm.')

Example

Input

Night
there is
closed

Output

Alarm!

Hint

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

Test 1

Test 2

Test 3

Test 4

Test 5

Test 6

Test 7

Test 8

Test 9

Test 10

Developer’s solution

# Получаем время суток от пользователя ('ночь' или 'день')
time_of_day = input()

# Получаем состояние датчика движения ('есть' или 'нет')
motion_sensor = input()

# Получаем состояние датчика дверей ('открыты' или 'закрыты')
door_sensor = input()

# Проверяем основное условие: сейчас ночь?
# И при этом сработал хотя бы один из датчиков (движение ИЛИ двери).
# Скобки важны, чтобы условие (motion_sensor == "есть" or door_sensor == "открыты") проверялось первым.
if time_of_day == "ночь" and (motion_sensor == "есть" or door_sensor == "открыты"):
    # Если условия выполнены, выводим сообщение о тревоге
    print("Тревога!")
else:
    # В противном случае (если сейчас день, или ночью все датчики в норме)
    # выводим сообщение, что все спокойно
    print("Все спокойно.")

🎉 Congratulations! 🎉

You did an excellent job with the task! It was a challenging problem, but you found the correct solution. You are one step closer to mastering programming! Keep up the good work, because every stage you pass makes you even stronger.