#56MediumLists & Tuples· Comprehensions

List Comprehension Challenges

A grid of sensor readings is stored as a list of rows. Some readings are missing and appear as `None`. Write `grid_summary(grid)` that returns a dictionary with three keys, in this order. Try to produce each value with a single comprehension: - `"flat"`: every reading that is not `None`, in reading order (row by row, left to right). - `"even_squares"`: the square of every even reading, in the same order. - `"row_sums"`: for each row, the sum of its readings that are not `None` (an empty row or a row of only `None` sums to 0).

Input format

`grid`: a list of lists whose items are integers or `None`.

Output format

A dictionary with keys `flat`, `even_squares` and `row_sums`.

Examples

Input: grid = [[1,2,null],[4,null,6]]

Output: {"flat":[1,2,4,6],"even_squares":[4,16,36],"row_sums":[3,10]}

Reading order skips the two `None` values; 2, 4 and 6 are even.

Input: grid = [[null],[],[-3,-4]]

Output: {"flat":[-3,-4],"even_squares":[16],"row_sums":[0,0,-7]}

-4 is even, so 16 is included. The first two rows sum to 0.

Constraints

0 <= len(grid) <= 100
0 <= len(row) <= 100
-1000 <= reading <= 1000

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Lists and Tuples in Python

#python
#list-comprehensions
#nested-lists