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Foundations of Python Programming: Functions First

Section 10.4 Nested Iteration

When you have nested data structures, especially lists and/or dictionaries, you will frequently need nested for loops to traverse them.
Line 3 executes once for each top-level list, three times in all. With each sub-list, line 5 executes once for each item in the sub-list. Try stepping through it in Codelens to make sure you understand what the nested iteration does.
Check Your Understanding

Checkpoint 10.4.1.

Now try rearranging these code fragments to make a function that counts all the leaf items in a nested list like nested1 above, the items at the lowest level of nesting (8 of them in nested1).

Checkpoint 10.4.2.

2. Below, we have provided a list of lists that contain information about people. Write code to create a new list that contains every person’s last name, and save that list as last_names.

Checkpoint 10.4.3.

3. Below, we have provided a list of lists named L. Use nested iteration to save every string containing “b” into a new list named b_strings.
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