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For the mission "How to find friends" , it’s nice to have access to a specially made data structure. In this mission we will realize a data structure which we will use to store and work with a friend network.

The class "Friends" should contains names and the connections between them. Names are represented as strings and are case sensitive. Connections are undirected, so if "sophia" is connected with "nikola", then it's also correct in reverse.

class Friends (connections)

Returns a new Friends instance. "connections" is an iterable of sets with two elements in each. Each connection contains two names as strings. Connections can be repeated in the initial data, but inside it's stored once. Each connection has only two states - existing or not.

>>> Friends(({"a", "b"}, {"b", "c"}, {"c", "a"}, {"a", "c"}))
>>> Friends([{"1", "2"}, {"3", "1"}])

add (connection)

Add a connection in the instance. "connection" is a set of two names (strings). Returns True if this connection is new. Returns False if this connection exists already.

>>> f = Friends([{"1", "2"}, {"3", "1"}])
>>> f.add({"1", "3"})
>>> f.add({"4", "5"})

remove (connection)

Remove a connection from the instance. "connection" is a set of two names (strings). Returns True if this connection exists. Returns False if this connection is not in the instance.

>>> f = Friends([{"1", "2"}, {"3", "1"}])
>>> f.remove({"1", "3"})
>>> f.remove({"4", "5"})

names ()

Returns a set of names. The set contains only names which are connected with somebody.

>>> f = Friends(({"a", "b"}, {"b", "c"}, {"c", "d"}))
>>> f.names()
{"a", "b", "c", "d"}
>>> f.remove({"d", "c"})
>>> f.names()
{"a", "b", "c"}

connected (name)

Returns a set of names which is connected with the given "name" . If "name" does not exist in the instance, then return an empty set.

>>> f = Friends(({"a", "b"}, {"b", "c"}, {"c", "a"}))
>>> f.connected("a")
{"b", "c"}
>>> f.connected("d")
>>> f.remove({"c", "a"})
>>> f.connected("c")
>>> f.remove({"c", "b"})
>>> f.connected("c")

In this mission all data will be correct and you don't need to implement value checking.

Input: Statements and expression with the Friends class.

Output: The behaviour as described.

How it is used: Here you will implement a class with mutable states. This is not a simple structure with a couple of functions, but object representation with more complex structure.

Precondition: All data is correct.

Invalid hot key. Each hot key should be unique and valid
Hot keys:
CheckiO Extensions

CheckiO Extensions allow you to use local files to solve missions. More info in a blog post.

In order to install CheckiO client you'll need installed Python (version at least 3.8)

Install CheckiO Client first:

pip3 install checkio_client

Configure your tool

checkio --domain=py config --key=

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checkio sync

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checkio serv -d

Alternatevly, you can install Chrome extension or FF addon

checkio install-plugin
checkio install-plugin --ff
checkio install-plugin --chromium

Read more here about other functionality that the checkio client provides. Feel free to submit an issue in case of any difficulties.

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