Python / Core Python Fundamentals Interview Questions
How does the for loop work in Python, and what is the role of range()?
Python's for loop iterates over any iterable — lists, strings, tuples, dictionaries, files, generators, and more. Unlike C-style for loops with an index counter, Python's loop just hands you each item in turn.
fruits = ['apple', 'banana', 'cherry'] for fruit in fruits: print(fruit) # Iterating a string character by character for ch in 'hello': print(ch)
range() generates a lazy sequence of integers and is the standard way to loop a fixed number of times. It takes up to three arguments: range(stop), range(start, stop), or range(start, stop, step). It never stores the full list in memory — it yields one integer at a time, making it memory-efficient even for range(10_000_000).
for i in range(5): # 0 1 2 3 4 print(i) for i in range(2, 10, 2): # 2 4 6 8 print(i)
When you need both the index and the value, use enumerate() instead of manually tracking a counter:
for idx, fruit in enumerate(fruits, start=1): print(idx, fruit) # 1 apple 2 banana 3 cherry
break exits the loop early; continue skips to the next iteration. A for loop can also have an else clause that runs only if the loop completed without hitting break — useful for search patterns.
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