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Loops: foreach loops (iterating over collections)

Following our exploration of Loops: while and do-while loops, this article focuses on what is often called a "foreach" loop in other languages. In Python, this is simply the standard for loop used to iterate over collections.

📚 Prerequisites​

A basic understanding of Python's for loop and common collection types (lists, tuples, dictionaries, sets).

🎯 Article Outline: What You'll Master​

In this article, you will learn:

  • ✅ How to iterate over lists and tuples.
  • ✅ How to iterate over dictionaries.
  • ✅ How to iterate over sets.
  • ✅ The concept of a "foreach" loop in Python.

🧠 Section 1: The "foreach" Loop in Python​

Python doesn't have a separate foreach keyword like some other languages. Instead, the standard for loop serves the same purpose. It's used to iterate over the items of any sequence or collection.

💻 Section 2: Iterating Over Lists and Tuples​

Iterating over lists and tuples is straightforward. The for loop will assign each item in the sequence to the loop variable.

Iterating over a list:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Iterating over a tuple:

colors = ("red", "green", "blue")
for color in colors:
    print(color)

🛠️ Section 3: Iterating Over Dictionaries​

When you iterate over a dictionary, you can access its keys, values, or both.

Iterating over keys (the default):

my_dict = {'a': 1, 'b': 2, 'c': 3}
for key in my_dict:
    print(key) # Output: a, b, c

Iterating over values:

for value in my_dict.values():
    print(value) # Output: 1, 2, 3

Iterating over key-value pairs:

for key, value in my_dict.items():
    print(f"key: {key}, value: {value}")

🔬 Section 4: Iterating Over Sets​

You can iterate over a set using a for loop, just like with a list or tuple. However, remember that sets are unordered, so the order in which the items are accessed is not guaranteed.

my_set = {"apple", "banana", "cherry"}
for item in my_set:
    print(item)

💡 Conclusion & Key Takeaways​

You've now learned how to use Python's for loop to iterate over various collection types, which is a fundamental skill for any Python programmer.

Let's summarize the key takeaways:

  • "foreach" in Python: The standard for loop is used to iterate over collections.
  • Lists and Tuples: Iterate over each item in the sequence.
  • Dictionaries: Iterate over keys, values, or key-value pairs.
  • Sets: Iterate over each item in the set, but the order is not guaranteed.

Challenge Yourself: Create a dictionary of your favorite foods and their ratings (e.g., "pizza": 10). Then, use a for loop to print each food and its rating.

➡️ Next Steps​

In the next article, we'll learn about "Loop Control: break and continue".

Happy coding!

Glossary (Python Terms)​

  • Collection: A group of objects, such as a list, tuple, dictionary, or set.
  • "foreach" loop: A loop that iterates over the items of a collection. In Python, this is the standard for loop.

Further Reading (Python Resources)​