THEORY AND PRACTICE

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Conditions

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Занятие 2. Conditions

Difficulty level:

Task«Mystical calendar»

in one of the ancient and mystical cities there is a library that contains a magic calendar predicting the events of the future. Every year in this calendar it can be of particular importance, and magicians of the city depend on accurate astronomical calculations. The sage Alista, the Keeper of the Library, entrusted you with an important task & mdash; Determine whether the specified year is a leap. This knowledge will help him correctly configure magic rites and predictions.

. . . .

Input format

The number of the year (integer).

Output format

The answer is whether the year is a leap (line: 'yes' or 'no').

Example

Input

2024

Output

Yes

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

# Считываем введенный год и преобразуем его в целое число
year = int(input())

# Проверяем условия високосного года, используя логические операторы "и" (and), "или" (or)
# Условие 1: Год делится на 4 без остатка (year % 4 == 0) И при этом не делится на 100 (year % 100 != 0)
# Условие 2: Год делится на 400 без остатка (year % 400 == 0)
if (year % 4 == 0 and year % 100 != 0) or (year % 400 == 0):
    # Если одно из двух основных условий истинно, то год високосный
    print("YES")
else:
    # В противном случае год обычный
    print("NO")

🎉 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.