For Loops

In Python, a for loop is used to iterate over a sequence (like a list, string, or range). Python lists can store mixed data types at runtime, making iteration very flexible.

Using range() for Repeats​

When we need to repeat an action a specific number of times, use range(). It creates an immutable sequence of numbers on the fly. It is memory efficient because it generates each number only when the loop asks for it.

for i in range(1, 4):
    print(f"Iteration #{i}")

Output:

Iteration #1
Iteration #2
Iteration #3

Why range() Is Memory Efficient​

Unlike a list, range() does not store all its numbers in memory at once. Generating range(1_000_000) uses the same tiny amount of memory as range(10).

Iterating Over Lists​

We can loop through a list directly without needing to manage an index variable. This is more readable and less prone to errors than index-based counters.

tech_stack = ["Python", "C", "Bash"]

for language in tech_stack:
    print(f"Learning {language}...")

Output:

Learning Python...
Learning C...
Learning Bash...

Mixed Types at Runtime​

Python is dynamically typed and doesn't enforce list element types at runtime. Even if we use a type hint like list[str], we can still store integers or floats in that list without the interpreter stopping we.

# Type hints are for developers and tools, not for the Python interpreter
mixed_list: list[str] = ["Aman", 101, 3.14]

for item in mixed_list:
    print(f"Item: {item} | Type: {type(item).__name__}")

Output:

Item: Aman | Type: str
Item: 101 | Type: int
Item: 3.14 | Type: float