Modules and Imports

A module is a file of Python code. Importing one makes its contents available.

import math

print(math.sqrt(16))
print(math.log2(1024))

Import forms

import math
print(math.pi)

from math import sqrt, log2
print(sqrt(16), log2(8))

import statistics as stats
print(stats.mean([1, 2, 3]))

import x keeps the module name as a prefix, which makes it obvious where a function came from. from x import y is shorter. Both are common; the alias form (import numpy as np) is standard for the scientific libraries.

Avoid from math import *. It hides which names exist and can overwrite your own variables.

Useful standard library modules

import statistics
import collections

depths = [30, 12, 45, 7, 30]
print(statistics.mean(depths))
print(statistics.median(depths))
print(collections.Counter("ATGGCC"))

collections.Counter counts occurrences and replaces the manual counting loop from the dictionaries lesson.

name

When a file runs directly, its __name__ is "__main__". When it is imported, __name__ is the module name. This is why scripts end with:

def main():
    print("running")


if __name__ == "__main__":
    main()

The code under that check runs when the file is executed, but not when another file imports it.

Task

Write stats_line(values). Use the statistics module. Return "n=<count> mean=<mean> median=<median>", with mean and median each rounded to 2 decimals. Return "n=0" for an empty list.