A course collects student IDs in separate class groups.
What You Need to Understand
Flattening combines nested sequences into a single-level list. A nested loop or comprehension preserves order and handles empty sublists predictably.
When to Use It
A course collects student IDs in separate class groups.
Step-by-Step Python Example
class_groups = [[101, 102], [], [103, 104]]
all_students = []
for group in class_groups:
all_students.extend(group)
print(all_students)How the Example Works
Each group contributes its members; the empty group adds nothing. The final list contains all four IDs.
Example Output
[101, 102, 103, 104]
[1, 2, 3]A Second Example
Compare this smaller variation with the main example, then experiment with your own values.
groups = [[1, 2], [3]]
print([value for group in groups for value in group])Important Behavior and Edge Cases
This is only one-level flattening. Strings are iterables too and will split into characters if incorrectly extended.
Try It Yourself
Rewrite the flattening loop as a nested comprehension.
Common Beginner Mistakes
- This is only one-level flattening. Strings are iterables too and will split into characters if incorrectly extended.
- Overlooking how an iterable is consumed, how element positions are chosen, or whether a function creates a new list.
Key Takeaways
- Flattening combines nested sequences into a single-level list.
- Each group contributes its members; the empty group adds nothing.
- This is only one-level flattening.