# Scalars

Scalar types represent concrete values at the leaves of a query. There are several built in types that Graphene provides out of the box which represent common values in Python. You can also create your own Scalar types to better express values that you might have in your data model.

All Scalar types accept the following arguments. All are optional:

`name`: string

> Override the name of the Field.

`description`: string

> A description of the type to show in the GraphiQL browser.

`required`: boolean

> If `True`, the server will enforce a value for this field. See NonNull. Default is `False`.

`deprecation_reason`: string

> Provide a deprecation reason for the Field.

`default_value`: any

> Provide a default value for the Field.

## Built in scalars

Graphene defines the following base Scalar Types that match the default GraphQL types:

### `graphene.String`

> Represents textual data, represented as UTF-8 character sequences. The String type is most often used by GraphQL to represent free-form human-readable text.

### `graphene.Int`

> Represents non-fractional signed whole numeric values. Int is a signed 32‐bit integer per the GraphQL spec

### `graphene.Float`

> Represents signed double-precision fractional values as specified by IEEE 754.

### `graphene.Boolean`

> Represents true or false.

### `graphene.ID`

> Represents a unique identifier, often used to refetch an object or as key for a cache. The ID type appears in a JSON response as a String; however, it is not intended to be human-readable. When expected as an input type, any string (such as “4”) or integer (such as 4) input value will be accepted as an ID.

Graphene also provides custom scalars for common values:

### `graphene.Date`

> Represents a Date value as specified by iso8601.

    import datetime
    from graphene import Schema, ObjectType, Date

    class Query(ObjectType):
        one_week_from = Date(required=True, date_input=Date(required=True))

        def resolve_one_week_from(root, info, date_input):
            assert date_input == datetime.date(2006, 1, 2)
            return date_input + datetime.timedelta(weeks=1)

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            oneWeekFrom(dateInput: "2006-01-02")
        }
    """)

    assert results.data == {"oneWeekFrom": "2006-01-09"}

### `graphene.DateTime`

> Represents a DateTime value as specified by iso8601.

    import datetime
    from graphene import Schema, ObjectType, DateTime

    class Query(ObjectType):
        one_hour_from = DateTime(required=True, datetime_input=DateTime(required=True))

        def resolve_one_hour_from(root, info, datetime_input):
            assert datetime_input == datetime.datetime(2006, 1, 2, 15, 4, 5)
            return datetime_input + datetime.timedelta(hours=1)

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            oneHourFrom(datetimeInput: "2006-01-02T15:04:05")
        }
    """)

    assert results.data == {"oneHourFrom": "2006-01-02T16:04:05"}

### `graphene.Time`

> Represents a Time value as specified by iso8601.

    import datetime
    from graphene import Schema, ObjectType, Time

    class Query(ObjectType):
        one_hour_from = Time(required=True, time_input=Time(required=True))

        def resolve_one_hour_from(root, info, time_input):
            assert time_input == datetime.time(15, 4, 5)
            tmp_time_input = datetime.datetime.combine(datetime.date(1, 1, 1), time_input)
            return (tmp_time_input + datetime.timedelta(hours=1)).time()

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            oneHourFrom(timeInput: "15:04:05")
        }
    """)

    assert results.data == {"oneHourFrom": "16:04:05"}

### `graphene.Decimal`

> Represents a Python Decimal value.

    import decimal
    from graphene import Schema, ObjectType, Decimal

    class Query(ObjectType):
        add_one_to = Decimal(required=True, decimal_input=Decimal(required=True))

        def resolve_add_one_to(root, info, decimal_input):
            assert decimal_input == decimal.Decimal("10.50")
            return decimal_input + decimal.Decimal("1")

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            addOneTo(decimalInput: "10.50")
        }
    """)

    assert results.data == {"addOneTo": "11.50"}

### `graphene.JSONString`

> Represents a JSON string.

    from graphene import Schema, ObjectType, JSONString, String

    class Query(ObjectType):
        update_json_key = JSONString(
            required=True,
            json_input=JSONString(required=True),
            key=String(required=True),
            value=String(required=True)
        )

        def resolve_update_json_key(root, info, json_input, key, value):
            assert json_input == {"name": "Jane"}
            json_input[key] = value
            return json_input

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            updateJsonKey(jsonInput: "{\\"name\\": \\"Jane\\"}", key: "name", value: "Beth")
        }
    """)

    assert results.data == {"updateJsonKey": "{\"name\": \"Beth\"}"}

### `graphene.Base64`

> Represents a Base64 encoded string.

    from graphene import Schema, ObjectType, Base64

    class Query(ObjectType):
        increment_encoded_id = Base64(
            required=True,
            base64_input=Base64(required=True),
        )

        def resolve_increment_encoded_id(root, info, base64_input):
            assert base64_input == "4"
            return int(base64_input) + 1

    schema = Schema(query=Query)

    results = schema.execute("""
        query {
            incrementEncodedId(base64Input: "NA==")
        }
    """)

    assert results.data == {"incrementEncodedId": "NQ=="}

## Custom scalars

You can create custom scalars for your schema. The following is an example for creating a DateTime scalar:

    import datetime
    from graphene.types import Scalar
    from graphql.language import ast

    class DateTime(Scalar):
        '''DateTime Scalar Description'''

        @staticmethod
        def serialize(dt):
            return dt.isoformat()

        @staticmethod
        def parse_literal(node, _variables=None):
            if isinstance(node, ast.StringValueNode):
                return datetime.datetime.strptime(
                    node.value, "%Y-%m-%dT%H:%M:%S.%f")

        @staticmethod
        def parse_value(value):
            return datetime.datetime.strptime(value, "%Y-%m-%dT%H:%M:%S.%f")

## Mounting Scalars

Scalars mounted in a `ObjectType`, `Interface` or `Mutation` act as `Field`s.

    class Person(graphene.ObjectType):
        name = graphene.String()

    # Is equivalent to:
    class Person(graphene.ObjectType):
        name = graphene.Field(graphene.String)

Note: when using the `Field` constructor directly, pass the type and not an instance.

Types mounted in a `Field` act as `Argument`s.

    graphene.Field(graphene.String, to=graphene.String())

    # Is equivalent to:
    graphene.Field(graphene.String, to=graphene.Argument(graphene.String))