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Lesson 7:
Mapping
Introduction to Vyper mapping
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Mapping
Mappings are data structures known has hash tables, that associate keys with values. They are declared as HashMap[KeyType, ValueType].
To look up a mapping value, you will need to use the keccak256 hash of the key data.
Note that mappings can only be declared as state variables.
# pragma version 0.4.0
# Notice you will need to define mapping variable using `HashMap` keyword
mapping_example: HashMap[uint256, String[100]]
# Example below maps key value "1" to "Hello, World!"
@external
def set_mapping_pair():
self.mapping_example[1] = "Hello, World!"
# Pass argument of "1" to deployed function below to view response
@external
@view
def get_mapping_value(x: uint256) -> String[100]:
return self.mapping_example[x]