Summary  
This chapter explains how to choose between for loops—used when you know the number of iterations or need to process each element in a sequence—and while loops—used for condition-driven or potentially infinite iterations that stop when a condition is met.

General domain of usage  
Travel planning (e.g., iterating a list of destinations, tracking travel costs against a budget, and accepting user-entered cities)

Loops are essential tools for repetitive tasks in Python, but deciding whether to use a `for` loop or a `while` loop depends on the nature of the task. Both have unique strengths that suit different scenarios.

A `for` loop is ideal when you know the exact number of iterations or are iterating through a sequence like a list, tuple, string, or range.

#### Iterating Over Sequences

When you need to process each element in a list, tuple, or string.

travel_list = ['Monako', 'Luxemburg', 'Liverpool', 'Barcelona', 'Munchen']

for city in travel_list:
    print(city)

#### Fixed Number of Iterations

When the number of iterations is predetermined.

for i in range(5):
    print('Trip', i + 1)

### When to Use `while` Loops

A `while` loop is better suited for situations where the number of iterations is unknown in advance, and the loop depends on a condition.


#### Condition-Based Iteration

When you want the loop to continue until a specific condition is met.

budget = 1000
travel_costs = [300, 150, 200, 400, 100]
total_cost = 0
i = 0

while total_cost + travel_costs[i] <= budget:
    total_cost += travel_costs[i]
    print('Trip', i + 1, 'cost:', travel_costs[i])
    i += 1

#### Infinite Loops with Exit Conditions

When you need an ongoing process that stops based on a condition.

``` python
while True:
    city = input("Enter a city (or 'stop' to end): ")
    if city == "stop":
        break
    print(f"City added: {city}")
```

The `f` before the quotation marks creates an **f-string**. It lets you insert variables into text using curly brackets, like `{city}`. You may see f-strings in other Python examples.

Note

Cleaner and more concise for iterating over sequences.

More flexible but can be harder to read if misused.

Iterating over lists, ranges, or sequences.

Higher risk without proper condition or increment logic.

Modify the code to stop the loop prematurely when a single trip exceeds $400. Where should you add the `break` statement?

Pythonのループをマスターして自信をつけましょう。forループやwhileループの基本から始め、ネストされたループ、制御文、動的条件などの高度な概念へと進みます。実践的な演習や実例を通じて、効率的でクリーンかつ強力なコードを書くスキルを身につけます。初心者やPythonの専門知識を磨きたい方に最適です。

forループを使用したシーケンスの反復方法の習得、range()の効果的な活用、if/elseによる条件分岐の探求、breakおよびcontinueによるループ制御。効率的でクリーンかつ実用的なコード作成に備え、楽しい課題に取り組む準備。

Choosing Between for and while Loops in Python

Iterating Over Sequences

Fixed Number of Iterations

When to Use while Loops

Condition-Based Iteration

Infinite Loops with Exit Conditions

When to Use `while` Loops