lesson 106 Modules & Packages · intermediate

Import styles: import, from and as

`import json` keeps a module's names behind its name, `from collections import Counter` brings one name in directly, and `as` renames. Each choice decides which names your code has, and which ones can collide.

You'll be able to

Explain what import x, from x import y and import x as z each bind in your program
Recognise ImportError for a name the module doesn't have
Spot and fix a clash where a later import or definition replaces an earlier name

The idea

Since the Collections & Itertools module you've written from collections import Counter. An import does two things: it finds the module and runs it (once per program), then it binds a name in your file. The style decides which name:

import json binds json, the module itself. You write json.dumps(...), so every call says where it comes from.
from collections import Counter binds just Counter. Shorter, but a reader has to look at the top of the file to know where it's from.
import statistics as stats binds the module under another name. Use it for long names or well-known conventions (you'll meet import pandas as pd later), and to avoid clashes.

Run each example to see what it prints. Running examples doesn't count toward progress.

example-1.py · Three ways to bring names in

import json
from collections import Counter
import statistics as stats

ratings = [5, 4, 5, 3, 5]
print(json.dumps({"ratings": ratings}))
print(Counter(ratings).most_common(1))
print(stats.median(ratings))

A name can only mean one thing at a time. from x import y and def y(...) both bind y, so the later one silently replaces the earlier. The classic case: the time module (for time.sleep) and the time type from datetime (a clock time like 09:30).

example-2.py · One name, two imports

import time
from datetime import time

opening = time(9, 30)
time.sleep(0.1)

example-3.py · Keep both, with as

import time
from datetime import time as clock_time

opening = clock_time(9, 30)
closing = clock_time(17, 0)
print(opening, closing, opening < closing)
pause = 0.01
time.sleep(pause)
print("slept for", pause, "seconds")

When to use which: import module when you use several of its names or the module name helps the reader (json.loads, csv.DictReader); from module import name for one or two names used often (Counter, Decimal); as for conventions and clashes. Put imports at the top of the file. Mistakes to avoid: importing two things with the same name, naming your own variable or function after something you imported, and from module import *, which dumps every name in and makes clashes invisible.

Review

import m binds the module (m.name), from m import name binds one name, as renames.
A name the module doesn't have raises ImportError; a later import or def with the same name replaces the earlier one.
Use the module name or as when two modules share a name.
Next: your own file as a module.

Practise this

The nearest store, using the geo module