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Mojo struct

Dict

A container that stores key-value pairs.

The key type and value type must be specified statically, unlike a Python dictionary, which can accept arbitrary key and value types.

The key type must implement the KeyElement trait, which encompasses Movable, Hashable, and EqualityComparable. It also includes CollectionElement and Copyable until we have references.

The value type must implement the CollectionElement trait.

Usage:

from collections import Dict
var d = Dict[String, Int]()
d["a"] = 1
d["b"] = 2
print(len(d))      # prints 2
print(d["a"])      # prints 1
print(d.pop("b"))  # prints 2
print(len(d))      # prints 1
from collections import Dict
var d = Dict[String, Int]()
d["a"] = 1
d["b"] = 2
print(len(d))      # prints 2
print(d["a"])      # prints 1
print(d.pop("b"))  # prints 2
print(len(d))      # prints 1

Parameters​

  • ​K (KeyElement): The type of the dictionary key. Must be Hashable and EqualityComparable so we can find the key in the map.
  • ​V (CollectionElement): The value type of the dictionary. Currently must be CollectionElement.

Aliases​

  • EMPTY = -1:
  • REMOVED = -2:

Fields​

  • ​size (Int): The number of elements currently stored in the dict.

Implemented traits​

AnyType, Boolable, CollectionElement, CollectionElementNew, Copyable, ExplicitlyCopyable, Movable, Sized

Methods​

__init__​

__init__(inout self: Self)

Initialize an empty dictiontary.

__init__(inout self: Self, *, power_of_two_initial_capacity: Int)

Initialize an empty dictiontary with a pre-reserved initial capacity.

Example usage:

var x = Dict[Int,Int](power_of_two_initial_capacity = 1024)
# Insert (2/3 of 1024) entries without reallocation.
var x = Dict[Int,Int](power_of_two_initial_capacity = 1024)
# Insert (2/3 of 1024) entries without reallocation.

Args:

  • ​power_of_two_initial_capacity (Int): At least 8, has to be a power of two.

__init__(inout self: Self, *, other: Self)

Copy an existing dictiontary.

Args:

  • ​other (Self): The existing dict.

__copyinit__​

__copyinit__(inout self: Self, existing: Self)

Copy an existing dictiontary.

Args:

  • ​existing (Self): The existing dict.

__moveinit__​

__moveinit__(inout self: Self, owned existing: Self)

Move data of an existing dict into a new one.

Args:

  • ​existing (Self): The existing dict.

__bool__​

__bool__(self: Self) -> Bool

Check if the dictionary is empty or not.

Returns:

False if the dictionary is empty, True if there is at least one element.

__getitem__​

__getitem__(self: Self, key: K) -> V

Retrieve a value out of the dictionary.

Args:

  • ​key (K): The key to retrieve.

Returns:

The value associated with the key, if it's present.

Raises:

"KeyError" if the key isn't present.

__setitem__​

__setitem__(inout self: Self, owned key: K, owned value: V)

Set a value in the dictionary by key.

Args:

  • ​key (K): The key to associate with the specified value.
  • ​value (V): The data to store in the dictionary.

__contains__​

__contains__(self: Self, key: K) -> Bool

Check if a given key is in the dictionary or not.

Args:

  • ​key (K): The key to check.

Returns:

True if there key exists in the dictionary, False otherwise.

__or__​

__or__(self: Self, other: Self) -> Self

Merge self with other and return the result as a new dict.

Args:

  • ​other (Self): The dictionary to merge with.

Returns:

The result of the merge.

__ior__​

__ior__(inout self: Self, other: Self)

Merge self with other in place.

Args:

  • ​other (Self): The dictionary to merge with.

fromkeys​

static fromkeys(keys: List[K, hint_trivial_type], value: V) -> Self

Create a new dictionary with keys from list and values set to value.

Args:

  • ​keys (List[K, hint_trivial_type]): The keys to set.
  • ​value (V): The value to set.

Returns:

The new dictionary.

static fromkeys(keys: List[K, hint_trivial_type], value: Optional[V] = #kgen.none) -> Dict[K, Optional[V]]

Create a new dictionary with keys from list and values set to value.

Args:

  • ​keys (List[K, hint_trivial_type]): The keys to set.
  • ​value (Optional[V]): The value to set.

Returns:

The new dictionary.

__iter__​

__iter__(ref [self_is_lifetime] self: Self) -> _DictKeyIter[$0, K, V, $1, 1]

Iterate over the dict's keys as immutable references.

Returns:

An iterator of immutable references to the dictionary keys.

__reversed__​

__reversed__(ref [self_is_lifetime] self: Self) -> _DictKeyIter[$0, K, V, $1, 0]

Iterate backwards over the dict keys, returning immutable references.

Returns:

A reversed iterator of immutable references to the dict keys.

__len__​

__len__(self: Self) -> Int

The number of elements currently stored in the dictionary.

Returns:

The number of elements currently stored in the dictionary.

__str__​

__str__[T: RepresentableKeyElement, U: RepresentableCollectionElement, //](self: Dict[T, U]) -> String

Returns a string representation of a Dict.

Note that since we can't condition methods on a trait yet, the way to call this method is a bit special. Here is an example below:

var my_dict = Dict[Int, Float64]()
my_dict[1] = 1.1
my_dict[2] = 2.2
dict_as_string = my_dict.__str__()
print(dict_as_string)
# prints "{1: 1.1, 2: 2.2}"
var my_dict = Dict[Int, Float64]()
my_dict[1] = 1.1
my_dict[2] = 2.2
dict_as_string = my_dict.__str__()
print(dict_as_string)
# prints "{1: 1.1, 2: 2.2}"

When the compiler supports conditional methods, then a simple str(my_dict) will be enough.

Note that both they keys and values' types must implement the __repr__() method for this to work. See the Representable trait for more information.

Parameters:

  • ​T (RepresentableKeyElement): The type of the keys in the Dict. Must implement the traits Representable and KeyElement.
  • ​U (RepresentableCollectionElement): The type of the values in the Dict. Must implement the traits Representable and CollectionElement.

Returns:

A string representation of the Dict.

find​

find(self: Self, key: K) -> Optional[V]

Find a value in the dictionary by key.

Args:

  • ​key (K): The key to search for in the dictionary.

Returns:

An optional value containing a copy of the value if it was present, otherwise an empty Optional.

get​

get(self: Self, key: K) -> Optional[V]

Get a value from the dictionary by key.

Args:

  • ​key (K): The key to search for in the dictionary.

Returns:

An optional value containing a copy of the value if it was present, otherwise an empty Optional.

get(self: Self, key: K, default: V) -> V

Get a value from the dictionary by key.

Args:

  • ​key (K): The key to search for in the dictionary.
  • ​default (V): Default value to return.

Returns:

A copy of the value if it was present, otherwise default.

pop​

pop(inout self: Self, key: K, owned default: V) -> V

Remove a value from the dictionary by key.

Args:

  • ​key (K): The key to remove from the dictionary.
  • ​default (V): A default value to return if the key was not found instead of raising.

Returns:

The value associated with the key, if it was in the dictionary. If it wasn't, return the provided default value instead.

pop(inout self: Self, key: K) -> V

Remove a value from the dictionary by key.

Args:

  • ​key (K): The key to remove from the dictionary.

Returns:

The value associated with the key, if it was in the dictionary. Raises otherwise.

Raises:

"KeyError" if the key was not present in the dictionary.

popitem​

popitem(inout self: Self) -> DictEntry[K, V]

Remove and return a (key, value) pair from the dictionary. Pairs are returned in LIFO order. popitem() is useful to destructively iterate over a dictionary, as often used in set algorithms. If the dictionary is empty, calling popitem() raises a KeyError.

Args: None

Returns:

Last dictionary item

Raises:

"KeyError" if the dictionary is empty.

keys​

keys(ref [self_is_lifetime] self: Self) -> _DictKeyIter[$0, K, V, $1, 1]

Iterate over the dict's keys as immutable references.

Returns:

An iterator of immutable references to the dictionary keys.

values​

values(ref [self_is_lifetime] self: Self) -> _DictValueIter[$0, K, V, $1, 1]

Iterate over the dict's values as references.

Returns:

An iterator of references to the dictionary values.

items​

items(ref [self_is_lifetime] self: Self) -> _DictEntryIter[$0, K, V, $1, 1]

Iterate over the dict's entries as immutable references.

These can't yet be unpacked like Python dict items, but you can access the key and value as attributes ie.

for e in dict.items():
    print(e[].key, e[].value)
for e in dict.items():
    print(e[].key, e[].value)

Returns:

An iterator of immutable references to the dictionary entries.

update​

update(inout self: Self, other: Self, /)

Update the dictionary with the key/value pairs from other, overwriting existing keys. The argument must be positional only.

Args:

  • ​other (Self): The dictionary to update from.

clear​

clear(inout self: Self)

Remove all elements from the dictionary.

setdefault​

setdefault(inout self: Self, key: K, owned default: V) -> Reference[1, V, *[0,0], 0]

Get a value from the dictionary by key, or set it to a default if it doesn't exist.

Args:

  • ​key (K): The key to search for in the dictionary.
  • ​default (V): The default value to set if the key is not present.

Returns:

The value associated with the key, or the default value if it wasn't present.

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