lesson 68 Built-ins & Sorting · intermediate

Ask about the whole collection with any and all

`any` is True when at least one item passes a test; `all` is True when every item does. Together they replace the flag-and-break loop.

You'll be able to

Write any(test for item in items) and all(test for item in items)
Know the empty case: any([]) is False, all([]) is True, and guard against it when that would be wrong
Combine any inside all for questions like *is every skill covered by someone?*

The idea

*Did any reading drop below freezing? Is every line of this order in stock?* With a loop you set a flag, test each item, and break once you know. any and all do exactly that.

Inside the call you can write a comprehension without square brackets: any(t < 0 for t in temps). That is a generator expression: it produces the test results one at a time, so any can stop at the first True, and all at the first False, without building a list.

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

example-1.py · Freezing, and the empty case

temps = [6.7, 7.2, -2.1, 3.9]
print(any(t < 0 for t in temps))
print(all(t < 10 for t in temps))
print(any([]), all([]))

That empty case is a real trap. An order with no lines would pass *every line is in stock* and get shipped as an empty box. Decide what an empty collection should mean, and check for it first.

example-2.py · Ready to ship?

def ready_to_ship(order):
    if not order["lines"]:
        return False
    return all(line["qty"] > 0 and line["in_stock"] for line in order["lines"])

full = {"lines": [{"qty": 2, "in_stock": True}, {"qty": 1, "in_stock": True}]}
waiting = {"lines": [{"qty": 2, "in_stock": True}, {"qty": 1, "in_stock": False}]}
empty = {"lines": []}
print(ready_to_ship(full), ready_to_ship(waiting), ready_to_ship(empty))

any and all take one collection. Two separate values are a different question, answered with or and and.

example-3.py · Two arguments to any

order = {"paid": True, "shipped": False}
print(any(order["paid"], order["shipped"]))

When to use it: validation (every field filled, any value negative), checks before an action, and coverage questions. Mistakes to avoid: forgetting that all of nothing is True; passing several values instead of one collection; and writing == True after the call: any(…) already is True or False.

Review

any(test for x in xs): at least one passes. all(...): every one passes. Both stop as soon as the answer is known.
any([]) is False and all([]) is True; guard the empty case when that is wrong for your problem.
Nest them for coverage questions: all(any(...) for ...).
Next: map and filter, and when a comprehension says the same thing more clearly.

Practise this