Visibility

Vyper have three types of decorator to declare a function's visibility.

@internal (default): can only be invoked within iself. The naming convention is to use _ prefix.
@external: allows external calls into this contract
@deploy: invoked once during contract deployment

# pragma version 0.4.0

# Using mapping example to demonstrate visibility decorators
mapping_example: HashMap[uint256, String[100]]

@deploy
def __init__():
    self.mapping_example[0] = "Deploy Decorator"

# This is an internal function that is invoked only when `setMappingPairOneAndTwo` is called
def _setMappingPairOne():
    self.mapping_example[1] = "Internal Decorator"

# Example below maps key value "1" to "Hello, World!"
@external
def setMappingPairOneAndTwo():
    self._setMappingPairOne()
    self.mapping_example[2] = "External Decorator"

# Only mapping_example[0] will have a value after contract deployment
# mapping_example[1] and mapping_example[2] will only have values after calling `setMappingPairOneAndTwo`
@external
@view
def viewMappingValue(x: uint256) -> String[100]:
    return self.mapping_example[x]

Vyper Differentiators

Do not need to explicitly declare @internal decorator as it is the default.
You will need to use @deploy decorator together with __init__() function to invoke the constructor. This is equivalent to Solidity's constructor keyword.

Visibility

Further Reading: