Transactional Key-Value Store

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Implement an in-memory key-value store as a class TxStore. Keys are lowercase strings and values are integers. Each test creates one TxStore and calls its methods in order; the result records every call's return value, including None. You build the store in stages: each part adds behavior on top of the previous parts, and all earlier behavior must keep working.

Part 1: Basic operations

Implement three methods on TxStore:

put(key, value) stores value under key, replacing any previous value. Returns None.
get(key) returns the value stored under key, or None if no value is stored.
delete(key) removes key and returns True if it was present, otherwise returns False.

Example 1
init
[]
operations
[["put",["a",5]],["get",["a"]],["get",["b"]],["delete",["a"]],["get",["a"]],["delete",["a"]]]
Output
[null,5,null,true,null,false]
Why: put(a,5) stores 5; get(a) returns 5; get(b) finds nothing; delete(a) removes the key and returns True; get(a) is then None, and the second delete(a) finds nothing and returns False.

Constraints

1 <= len(operations) <= 10^4
1 <= len(key) <= 10
'a' <= key[i] <= 'z'
-10^9 <= value <= 10^9