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Leçon 2. Conditions
Difficulté :
Exercice«Voyage en voiture»
💻 Python
Alexey est un passionné de voyages en voiture. Il planifie son prochain grand voyage et veut s'assurer qu'il pourra atteindre la première grande ville sans s'arrêter pour faire le plein.
Avant le voyage, il doit savoir s'il y a assez d'essence dans le réservoir. Aidez Alexey et écrivez un programme pour lui.
Données connues :
- La consommation de carburant de sa voiture est exactement de 10 litres aux 100 kilomètres .
- Par sécurité, Alexey laisse toujours dans le réservoir au moins 5 litres comme réserve de secours.
Écrivez un programme qui demande deux valeurs à l'utilisateur : la quantité actuelle de carburant dans le réservoir (en litres) et la distance jusqu'à la destination (en kilomètres). Le programme doit analyser ces données et afficher l'un des deux messages : « Il y a assez de carburant, vous pouvez partir ! » ou « Faites le plein... »
Format d entrée
Première ligne : le niveau de carburant actuel dans le réservoir (nombre réel, litres).
Deuxième ligne : la distance jusqu'à la destination, en kilomètres).
Format de sortie
Un message concernant la suffisance en carburant (ligne).
Exemple
Entrée
50.0
400.0
Sortie
Le carburant est suffisant, vous pouvez y aller !
Indice
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
Solution du développeur
# Получаем от пользователя текущее количество топлива в литрах и преобразуем в число
current_fuel = float(input())
# Получаем от пользователя расстояние до цели в километрах и преобразуем в число
distance = float(input())
# Рассчитываем, сколько литров топлива потребуется на всю дистанцию
# Расход 10л/100км - это то же самое, что расстояние / 10
fuel_needed = distance / 10
# Проверяем условие: хватит ли топлива с учетом запаса в 5 литров.
# То есть, текущее топливо должно быть больше или равно сумме необходимого на поездку и запаса.
if current_fuel >= fuel_needed + 5:
# Если топлива достаточно, выводим соответствующее сообщение
print("Топлива хватит, можно ехать!")
else:
# Если топлива недостаточно, выводим другое сообщение
print("Нужна дозаправка.")
