Session

---

Calls

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purge_keys

Removes any session key(s) of the function caller.

This doesn't take effect until the next session.

The dispatch origin of this function must be Signed and the account must be either be convertible to a validator ID using the chain's typical addressing system (this usually means being a controller account) or directly convertible into a validator ID (which usually means being a stash account).

## Complexity - O(1) in number of key types. Actual cost depends on the number of length of T::Keys::key_ids() which is fixed.

Attributes

No attributes

Python

call = substrate.compose_call(
    'Session', 'purge_keys', {}
)

---

set_keys

Sets the session key(s) of the function caller to keys. Allows an account to set its session key prior to becoming a validator. This doesn't take effect until the next session.

The dispatch origin of this function must be signed.

## Complexity - O(1). Actual cost depends on the number of length of T::Keys::key_ids() which is fixed.

Attributes

Name	Type
keys	T::Keys
proof	Vec<u8>

Python

call = substrate.compose_call(
    'Session', 'set_keys', {
    'keys': {
        'aura': '[u8; 32]',
        'nimbus': '[u8; 32]',
        'vrf': '[u8; 32]',
    },
    'proof': 'Bytes',
}
)

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Events

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NewSession

New session has happened. Note that the argument is the session index, not the block number as the type might suggest.

Attributes

Name	Type	Composition
session_index	SessionIndex	u32

---

Storage functions

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CurrentIndex

Current index of the session.

Python

result = substrate.query(
    'Session', 'CurrentIndex', []
)

Return value

'u32'

---

DisabledValidators

Indices of disabled validators.

The vec is always kept sorted so that we can find whether a given validator is disabled using binary search. It gets cleared when on_session_ending returns a new set of identities.

Python

result = substrate.query(
    'Session', 'DisabledValidators', []
)

Return value

['u32']

---

KeyOwner

The owner of a key. The key is the KeyTypeId + the encoded key.

Python

result = substrate.query(
    'Session', 'KeyOwner', [('[u8; 4]', 'Bytes')]
)

Return value

'AccountId'

---

NextKeys

The next session keys for a validator.

Python

result = substrate.query(
    'Session', 'NextKeys', ['AccountId']
)

Return value

{'aura': '[u8; 32]', 'nimbus': '[u8; 32]', 'vrf': '[u8; 32]'}

---

QueuedChanged

True if the underlying economic identities or weighting behind the validators has changed in the queued validator set.

Python

result = substrate.query(
    'Session', 'QueuedChanged', []
)

Return value

'bool'

---

QueuedKeys

The queued keys for the next session. When the next session begins, these keys will be used to determine the validator's session keys.

Python

result = substrate.query(
    'Session', 'QueuedKeys', []
)

Return value

[('AccountId', {'aura': '[u8; 32]', 'nimbus': '[u8; 32]', 'vrf': '[u8; 32]'})]

---

Validators

The current set of validators.

Python

result = substrate.query(
    'Session', 'Validators', []
)

Return value

['AccountId']

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Errors

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DuplicatedKey

Registered duplicate key.

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InvalidProof

Invalid ownership proof.

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NoAccount

Key setting account is not live, so it's impossible to associate keys.

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NoAssociatedValidatorId

No associated validator ID for account.

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NoKeys

No keys are associated with this account.

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