A Door With Legal Transitions Only

Medium ⏱ 12 min 62% acceptance ★★★★★ 4.7

Model a door: states 'open', 'closed', 'locked'. Door starts closed; open(), close(), lock(), unlock() mutate state but illegal moves raise ValueError (can't open a locked door, can't lock an open one, unlock only works when locked). Each method returns the new state.

Examples

Example 1

Input

d = Door(); d.lock(); d.open()

Output

ValueError after 'locked'

Explanation

Opening a locked door is illegal.

Example 2

Input

Door().open()

Output

'open'

Explanation

A closed door opens fine.

Constraints

Exactly the three states.
Illegal transitions raise ValueError.

Topics

OOPstate modeling

Companies

TeslaBoschHoneywell

Hints

Hint 1

Guard each method with a state check.

Hint 2

Return self.state at the end of each.

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