Write and test Python programs

Make the algorithm explicit

A function groups a calculation under a name and receives input through parameters. The example counts values at or above a threshold. The local count starts at zero on each call, and return passes the result back without printing it.

Python sequences use zero-based indexing. A for-each traversal is useful when only the value matters; use an index when the position is needed. Indentation defines the body of a condition, loop, or function.

def count_at_least(values, threshold):
    count = 0
    for value in values:
        if value >= threshold:
            count += 1
    return count

print(count_at_least([40, 50, 80], 50))

Choose tests that expose mistakes

For this function, test an empty list, no qualifying values, all qualifying values, and a value equal to the threshold. The equality case distinguishes >= from >. State the expected result before running the program.

Separate input and output from the calculation so the same algorithm is easy to test with different values. If reading a file, define how malformed records and missing data will be handled before including them in the analysis.

Check yourself