Standard Library Types
This section enumerates the supported built-in and standard library types: the allowed values, the possible constraints, and whether strictness can be configured.
See also the conversion table for a summary of the allowed values for each type.
Note
Unless specified otherwise, values are serialized as-is, in both Python and JSON modes.
Booleans¶
Built-in type: bool
Validation
- A valid
boolinstance, i.e.TrueorFalse. - The integers
0or1. - A string, which when converted to lowercase is one of
'0','off','f','false','n','no','1','on''t','true','y','yes'. bytesobjects that are valid per the previous rule when decoded to a string.
Strictness
In strict mode, only boolean values are valid. Pydantic provides the StrictBool
type as a convenience to using the Strict() metadata class.
Example
from pydantic import BaseModel, ValidationError
class BooleanModel(BaseModel):
bool_value: bool
print(BooleanModel(bool_value=False))
#> bool_value=False
print(BooleanModel(bool_value='False'))
#> bool_value=False
print(BooleanModel(bool_value=1))
#> bool_value=True
try:
BooleanModel(bool_value=[])
except ValidationError as e:
print(str(e))
"""
1 validation error for BooleanModel
bool_value
Input should be a valid boolean [type=bool_type, input_value=[], input_type=list]
"""
Strings¶
Built-in type: str
Validation
- Strings are accepted as-is.
bytesandbytearrayare decoded to UTF-8 strings.- Enums are converted using the
valueattribute, by callingstr()on it. - If
coerce_numbers_to_stris set, any number type (int,floatandDecimal) will be coerced to a string and accepted as-is.
Constraints
Strings support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
pattern |
A regex pattern that the string must match | pattern keyword (see note below). |
min_length |
The minimum length of the string | minLength keyword |
max_length |
The maximum length of the string | maxLength keyword |
strip_whitespace |
Whether to remove leading and trailing whitespace | N/A |
to_upper |
Whether to convert the string to uppercase | N/A |
to_lower |
Whether to convert the string to lowercase | N/A |
These constraints can be provided using the StringConstraints metadata type, or using the Field() function (except for to_upper and to_lower).
The MinLen, MaxLen, Len, LowerCase, UpperCase metadata types from the annotated-types
library can also be used.
pattern constraint
By default, Pydantic will use the regex Rust crate to enforce the pattern constraint. The regex engine can be controlled
using the regex_engine configuration value. If a compiled regular expression object is used for
pattern, the Python engine will automatically be used.
While the JSON Schema specification recommends using patterns valid according to dialect described in ECMA-262, Pydantic will not enforce it.
Strictness
In strict mode, only string values are valid. Pydantic provides the StrictStr
type as a convenience to using the Strict() metadata class.
Example
from typing import Annotated
from pydantic import BaseModel, StringConstraints
class StringModel(BaseModel):
str_value: str = ""
constrained_str_value: Annotated[str, StringConstraints(to_lower=True)] = ""
print(StringModel(str_value="test").str_value)
#> test
print(StringModel(constrained_str_value='TEST').constrained_str_value)
#> test
Bytes¶
Built-in type: bytes.
See also: ByteSize.
Validation
bytesinstances are validated as is.- Strings and
bytearrayinstances are converted as bytes, following theval_json_bytesconfiguration value (despite its name, it applies to both Python and JSON modes).
Constraints
Strings support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The minimum length of the bytes | minLength keyword |
max_length |
The maximum length of the bytes | maxLength keyword |
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only bytes instances are valid. Pydantic provides the StrictBytes
type as a convenience to using the Strict() metadata class.
In JSON mode, strict mode has no effect.
Numbers¶
Pydantic supports the following numeric types from the Python standard library:
Integers¶
Built-in type: int.
Validation
- Integers are validated as-is.
- Strings and bytes are attempted to be converted to integers and validated as-is (see the jiter implementation for details).
- Floats are validated as integers, provided the float input is not infinite or a NaN (not-a-number) and the fractional part is 0.
Decimalinstances, provided they are finite and the denominator is 1.Fractioninstances, provided they are integers.- Enums are converted using the
valueattribute.
Constraints
Integers support the following constraints (numbers must be coercible to integers):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this number | maximum keyword |
ge |
The value must be greater than or equal to this number | minimum keyword |
lt |
The value must be strictly less than this number | exclusiveMaximum keyword |
gt |
The value must be strictly greater than this number | exclusiveMinimum keyword |
multiple_of |
The value must be a multiple of this number | multipleOf keyword |
These constraints can be provided using the Field() function.
The Le, Ge, Lt, Gt and MultipleOf metadata types from the annotated-types
library can also be used.
Pydantic also provides the following types to further constrain the allowed integer values:
PositiveInt: Requires the input to be greater than zero.NegativeInt: Requires the input to be less than zero.NonPositiveInt: Requires the input to be less than or equal to zero.NonNegativeInt: Requires the input to be greater than or equal to zero.
Strictness
In strict mode, only integer values are valid. Pydantic provides the StrictInt
type as a convenience to using the Strict() metadata class.
Floats¶
Built-in type: float.
Validation
- Floats are validated as-is.
- String and bytes are attempted to be converted to floats and validated as-is. (see the Rust implementation for details).
- If the input has a
__float__()method, it will be called to convert the input into a float. If__float__()is not defined, it falls back to__index__(). This includes (but not limited to) theDecimalandFractiontypes.
Constraints
Floats support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this number | maximum keyword |
ge |
The value must be greater than or equal to this number | minimum keyword |
lt |
The value must be strictly less than this number | exclusiveMaximum keyword |
gt |
The value must be strictly greater than this number | exclusiveMinimum keyword |
multiple_of |
The value must be a multiple of this number | multipleOf keyword |
allow_inf_nan |
Whether to allow NaN (not-a-number) and infinite values | N/A |
These constraints can be provided using the Field() function.
The Le, Ge, Lt, Gt and MultipleOf metadata types from the annotated-types
library and the AllowInfNan type can also be used.
Pydantic also provides the following types as convenience aliases:
PositiveFloat: Requires the input to be greater than zero.NegativeFloat: Requires the input to be less than zero.NonPositiveFloat: Requires the input to be less than or equal to zero.NonNegativeFloat: Requires the input to be greater than or equal to zero.FiniteFloat: Prevents NaN (not-a-number) and infinite values.
Strictness
In strict mode, only float values and inputs having a __float__()
or __index__() method are valid.
Pydantic provides the StrictFloat type as a convenience to
using the Strict() metadata class.
Integer enums¶
Standard library type: enum.IntEnum.
Validation
- If the
enum.IntEnumtype is used directly, anyenum.IntEnuminstance is validated as-is - Id an
enum.IntEnumsubclass is used as a type, any enum member or value that correspond to the enum members values is validated as-is.
See Enums for more details.
Decimals¶
Standard library type: decimal.Decimal.
Validation
Decimalinstances are validated as is.- Any value accepted by the
Decimalconstructor (apart from the three-tuple input) will validate.
Constraints
Decimals support the following constraints (numbers must be coercible to decimals):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this number | maximum keyword |
ge |
The value must be greater than or equal to this number | minimum keyword |
lt |
The value must be strictly less than this number | exclusiveMaximum keyword |
gt |
The value must be strictly greater than this number | exclusiveMinimum keyword |
multiple_of |
The value must be a multiple of this number | multipleOf keyword |
allow_inf_nan |
Whether to allow NaN (not-a-number) and infinite values | N/A |
max_digits |
The maximum number of decimal digits allowed. The zero before the decimal point and trailing zeros are not counted. | pattern keyword, to describe the string pattern |
decimal_places |
The maximum number of decimal places allowed. Trailing zeros are not counted. | pattern keyword, to describe the string pattern |
Note that the JSON Schema pattern keyword will be specified
in the JSON Schema to describe the string pattern in all cases (and can vary if max_digits and/or decimal_places is specified).
These constraints can be provided using the Field() function.
The Le, Ge, Lt, Gt and MultipleOf metadata types from the annotated-types
library and the AllowInfNan type can also be used.
Strictness
In strict mode, only decimal.Decimal instances are accepted. In JSON mode, strict mode has no effect.
Serialization
In Python mode, Decimal instances are
serialized as is.
In JSON mode, they are serialized as strings. A serializer can be used to override this behavior:
from decimal import Decimal
from typing import Annotated
from pydantic import BaseModel, PlainSerializer
class Model(BaseModel):
f: Annotated[Decimal, PlainSerializer(float, when_used='json')]
my_model = Model(f=Decimal('2.1'))
print(my_model.model_dump()) # (1)!
#> {'f': Decimal('2.1')}
print(my_model.model_dump_json()) # (2)!
#> {"f":2.1}
- In Python mode,
fremains aDecimalinstance. - In JSON mode,
fis serialized as a float.
Complex numbers¶
Built-in type: complex.
Validation
complexinstances are validated as-is.- Strings are validated using the
complex()constructor. - Numbers (integers and floats) are used as the real part.
- Objects defining
__complex__(),__float__(). or__index__()are currently not accepted.
Strictness
In strict mode, only complex instances are accepted. In JSON mode, only strings that are
accepted by the complex() constructor are allowed.
Serialization
In Python mode, complex instances are
serialized as is.
In JSON mode, they are serialized as strings.
Fractions¶
Standard library type: fractions.Fraction.
Validation
Fractioninstances are validated as is.- Floats, strings and
decimal.Decimalinstances are validated using theFraction()constructor.
Strictness
In strict mode, only Fraction instances are accepted. In JSON mode, strict mode has no effect.
Serialization
Fractions are serialized as strings, both in Python and JSON modes.
Date and time types¶
Pydantic supports the following date and time
types from the datetime standard library:
Datetimes¶
Standard library type: datetime.datetime.
Validation
datetimeinstances are validated as is.- Strings and bytes are validated in two ways:
- Strings complying to the RFC 3339 format (both datetime and date). See the speedate documentation for more details.
- Unix timestamps, both as seconds or milliseconds sinch the epoch.
See the
val_temporal_unitconfiguration value for more details.
- Integers and floats (or types that can be coerced as integers or floats) are validated as unix timestamps, following the same semantics as strings.
datetime.dateinstances are accepted, and converted to adatetimeinstance by setting thehour,minute,secondandmicrosecondattributes to0, and thetzinfoattribute toNone.
Note
Named timezone support (as specified in RFC 9557) can be tracked in this issue.
Serialization
In Python mode, datetime instances are
serialized as is.
In JSON mode, they are serialized as strings.
Constraints
Datetimes support the following constraints (constraint values must be coercible to a datetime instance):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this datetime | N/A |
ge |
The value must be greater than or equal to this datetime | N/A |
lt |
The value must be strictly less than this datetime | N/A |
gt |
The value must be strictly greater than this datetime | N/A |
These constraints can be provided using the Field() function.
The Le, Ge, Lt and Gt metadata types from the annotated-types
library can also be used.
Pydantic also provides the following types to further constrain the allowed datetime values:
AwareDatetime: Requires the input to have a timezone.NaiveDatetime: Requires the input to not have a timezone.PastDatetime: Requires the input to be in the past when validated.FutureDatetime: Requires the input to be in the future when validated.
Strictness
In strict mode, only datetime instances are accepted. In JSON mode, only strings complying to the
RFC 3339 format (only datetime) or as unix timestamps are accepted.
Example
from datetime import datetime
from typing import Annotated
from pydantic import AwareDatetime, BaseModel, Field
class Event(BaseModel):
dt: Annotated[AwareDatetime, Field(gt=datetime(2000, 1, 1))]
event = Event(dt='2032-04-23T10:20:30.400+02:30')
print(event.model_dump())
"""
{'dt': datetime.datetime(2032, 4, 23, 10, 20, 30, 400000, tzinfo=TzInfo(9000))}
"""
print(event.model_dump_json())
#> {"dt":"2032-04-23T10:20:30.400000+02:30"}
Dates¶
Standard library type: datetime.date.
Validation
dateinstances are validated as is.- Strings and bytes are validated in two ways:
- Strings complying to the RFC 3339 date format. See the speedate documentation for more details.
- Unix timestamps, both as seconds or milliseconds sinch the epoch.
See the
val_temporal_unitconfiguration value for more details.
- If the validation fails, the input can be validated as a datetime (including as numbers), provided that the time component is 0 and that it is naive.
Serialization
In Python mode, date instances are
serialized as is.
In JSON mode, they are serialized as strings.
Constraints
Dates support the following constraints (constraint values must be coercible to a date instance):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this date | N/A |
ge |
The value must be greater than or equal to this date | N/A |
lt |
The value must be strictly less than this date | N/A |
gt |
The value must be strictly greater than this date | N/A |
These constraints can be provided using the Field() function.
The Le, Ge, Lt and Gt metadata types from the annotated-types
library can also be used.
Pydantic also provides the following types to further constrain the allowed date values:
PastDate: Requires the input to be in the past when validated.FutureDate: Requires the input to be in the future when validated.
Strictness
In strict mode, only date instances are accepted. In JSON mode, only strings complying to the
RFC 3339 format (only date) or as unix timestamps are accepted.
Example
from datetime import date
from pydantic import BaseModel
class Birthday(BaseModel):
d: date
my_birthday = Birthday(d=1679616000.0)
print(my_birthday.model_dump())
#> {'d': datetime.date(2023, 3, 24)}
print(my_birthday.model_dump_json())
#> {"d":"2023-03-24"}
Time¶
Standard library type: datetime.time.
Validation
timeinstances are validated as is.- Strings and bytes are validated according to the RFC 3339 time format.
- Integers and floats (or values that can be coerced to such numbers) are validated as seconds. The value should not exceed 86 399.
Serialization
In Python mode, time instances are
serialized as is.
In JSON mode, they are serialized as strings.
Note
Named timezones from the IANA time zone database (see the zoneinfo module) are not serialized
with time objects. This is consistent with the time.isoformat() method.
Constraints
Time support the following constraints (constraint values must be coercible to a time instance):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this time | N/A |
ge |
The value must be greater than or equal to this time | N/A |
lt |
The value must be strictly less than this time | N/A |
gt |
The value must be strictly greater than this time | N/A |
These constraints can be provided using the Field() function.
The Le, Ge, Lt and Gt metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only time instances are accepted. In JSON mode, only strings complying to the
RFC 3339 format are accepted.
Example
from datetime import time
from pydantic import BaseModel
class Meeting(BaseModel):
t: time
m = Meeting(t=time(4, 8, 16))
print(m.model_dump())
#> {'t': datetime.time(4, 8, 16)}
print(m.model_dump_json())
#> {"t":"04:08:16"}
Timedeltas¶
Standard library type: datetime.timedelta.
Validation
timedeltainstances are validated as is.- Strings and bytes are validated according to the RFC 3339 time format.
- Integers and floats (or values that can be coerced to such numbers) are validated as seconds.
Constraints
Timedeltas support the following constraints (constraint values must be coercible to a timedata instance):
| Constraint | Description | JSON Schema |
|---|---|---|
le |
The value must be less than or equal to this timedelta | N/A |
ge |
The value must be greater than or equal to this timedelta | N/A |
lt |
The value must be strictly less than this timedelta | N/A |
gt |
The value must be strictly greater than this timedelta | N/A |
These constraints can be provided using the Field() function.
The Le, Ge, Lt and Gt metadata types from the annotated-types
library can also be used.
Serialization
In Python mode, timedelta instances are
serialized as is.
In JSON mode, they are serialized as strings.
Strictness
In strict mode, only timedelta instances are accepted. In JSON mode, only strings complying to the
RFC 3339 format are accepted.
Example
from datetime import timedelta
from pydantic import BaseModel
class Model(BaseModel):
td: timedelta
m = Model(td='P3DT12H30M5S')
print(m.model_dump())
#> {'td': datetime.timedelta(days=3, seconds=45005)}
print(m.model_dump_json())
#> {"td":"P3DT12H30M5S"}
Enums¶
Standard library type: enum.Enum.
Validation
- If the
enum.Enumtype is used directly, anyenum.Enuminstance is validated as-is. - Id an
enum.Enumsubclass is used as a type, any enum member or value that correspond to the enum members values is validated as-is.
Serialization
In Python mode, enum instances are serialized as is.
The use_enum_values configuration value can be set to
use the enum value during validation (so that it is also used during serialization).
In JSON mode, enum instances are serialized using their value.
Example
from enum import Enum, IntEnum
from pydantic import BaseModel, ValidationError
class FruitEnum(str, Enum):
PEAR = 'pear'
BANANA = 'banana'
class ToolEnum(IntEnum):
SPANNER = 1
WRENCH = 2
class CookingModel(BaseModel):
fruit: FruitEnum = FruitEnum.PEAR
tool: ToolEnum = ToolEnum.SPANNER
print(CookingModel())
#> fruit=<FruitEnum.PEAR: 'pear'> tool=<ToolEnum.SPANNER: 1>
print(CookingModel(tool=2, fruit='banana'))
#> fruit=<FruitEnum.BANANA: 'banana'> tool=<ToolEnum.WRENCH: 2>
try:
CookingModel(fruit='other')
except ValidationError as e:
print(e)
"""
1 validation error for CookingModel
fruit
Input should be 'pear' or 'banana' [type=enum, input_value='other', input_type=str]
"""
None types¶
Supported types: None, NoneType or Literal[None] (they are equivalent).
Allows only None as a value.
Generic collection types¶
Pydantic supports a wide variety of generic collection types, both built-ins (such as list) and abstract base classes
from the collections.abc module (such as Sequence).
In most cases, it is recommended to make use of the built-in types over the abstract ones. Due to data coercion,
using list or tuple will allow most other iterables as input, with better performance.
Strictness on collection types
When applying strict mode on collection types, strictness will not apply to the inner types. This may change in the future, see this issue.
Lists¶
Built-in type: list (deprecated alias: typing.List).
Validation
- Allows
list,tuple,setandfrozensetinstances, or any iterable that is not a string, bytes, bytearray, dict or mapping. Produces alistinstance. - If a generic parameter is provided, the appropriate validation is applied to all items of the list.
Constraints
Lists support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The list must have at least this many items | minItems keyword |
max_length |
The list must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only list instances are valid. Strict mode does not apply to the items of the list.
The strict constraint must be applied to the parameter type for this to work.
Example
from typing import Optional
from pydantic import BaseModel, Field
class Model(BaseModel):
simple_list: Optional[list[object]] = None
list_of_ints: Optional[list[int]] = Field(default=None, strict=True)
print(Model(simple_list=('1', '2', '3')).simple_list)
#> ['1', '2', '3']
print(Model(list_of_ints=['1', 2, 3]).list_of_ints)
#> [1, 2, 3]
from pydantic import BaseModel, Field
class Model(BaseModel):
simple_list: list[object] | None = None
list_of_ints: list[int] | None = Field(default=None, strict=True)
print(Model(simple_list=('1', '2', '3')).simple_list)
#> ['1', '2', '3']
print(Model(list_of_ints=['1', 2, 3]).list_of_ints)
#> [1, 2, 3]
Tuples¶
Built-in type: tuple (deprecated alias: typing.Tuple).
Note
Unpacked tuple types (as specified by PEP 646) are not yet supported, and can be tracked in this issue.
Validation
- Allows
tuple,list,setandfrozensetinstances, or any iterable that is not a string, bytes, bytearray, dict or mapping. Produces atupleinstance. - Appropriate validation is applied to items of the tuple, if element types are specified.
Constraints
Lists support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The tuple must have at least this many items | minItems keyword |
max_length |
The tuple must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Additionally, the prefixItems JSON Schema keyword may be used
depending on the tuple shape.
Strictness
In strict mode, only tuple instances are valid. Strict mode does not apply to the items of the tuple.
The strict constraint must be applied to the parameter types for this to work.
Example
from typing import Optional
from pydantic import BaseModel
class Model(BaseModel):
simple_tuple: Optional[tuple] = None
tuple_of_different_types: Optional[tuple[int, float, bool]] = None
print(Model(simple_tuple=[1, 2, 3, 4]).simple_tuple)
#> (1, 2, 3, 4)
print(Model(tuple_of_different_types=[3, 2, 1]).tuple_of_different_types)
#> (3, 2.0, True)
from pydantic import BaseModel
class Model(BaseModel):
simple_tuple: tuple | None = None
tuple_of_different_types: tuple[int, float, bool] | None = None
print(Model(simple_tuple=[1, 2, 3, 4]).simple_tuple)
#> (1, 2, 3, 4)
print(Model(tuple_of_different_types=[3, 2, 1]).tuple_of_different_types)
#> (3, 2.0, True)
Named tuples¶
Standard library type: typing.NamedTuple (and types created by the collections.namedtuple() factory function
– each field will implicitly have the type Any).
Validation
- Allows
tupleandlistinstances. Validate each item according to the field definition. - Allows
dictinstances. Keys must match the named tuple field names, and values are validated according to the field definition.
Serialization
In Python mode, named tuples are serialized as tuples. In JSON mode, they are serialized as arrays.
Example
from typing import NamedTuple
from pydantic import BaseModel
class Point(NamedTuple):
x: int
y: int
class Model(BaseModel):
p: Point
model = Model(p=('1', 2))
print(model.model_dump())
#> {'p': (1, 2)}
Sets¶
Types: set (or collections.abc.MutableSet) and frozenset (or collections.abc.Set)
(deprecated aliases: typing.Set and typing.FrozenSet).
Validation
- Allows
set,frozenset,tupleandlistinstances, or any iterable that is not a string, bytes, bytearray, dict or mapping. Produces asetorfrozensetinstance. - If a generic parameter is provided, the appropriate validation is applied to all items of the set/frozenset.
Constraints
Sets support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The set must have at least this many items | minItems keyword |
max_length |
The set must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only set/frozenset instances are valid. Strict mode does not apply to the items of the set.
The strict constraint must be applied to the parameter type for this to work.
Serialization
In Python mode, sets are serialized as is. In JSON mode, they are serialized as arrays.
Example
from typing import Optional
from pydantic import BaseModel
class Model(BaseModel):
simple_set: Optional[set] = None
set_of_ints: Optional[frozenset[int]] = None
print(Model(simple_set=['1', '2', '3']).simple_set)
#> {'1', '2', '3'}
print(Model(set_of_ints=['1', '2', '3']).set_of_ints)
#> frozenset({1, 2, 3})
from pydantic import BaseModel
class Model(BaseModel):
simple_set: set | None = None
set_of_ints: frozenset[int] | None = None
print(Model(simple_set=['1', '2', '3']).simple_set)
#> {'1', '2', '3'}
print(Model(set_of_ints=['1', '2', '3']).set_of_ints)
#> frozenset({1, 2, 3})
Deque¶
Standard library type: collections.deque (deprecated alias: typing.Deque).
Validation
Values are first validated as a list, and then passed to the deque constructor.
Constraints
Deques support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The deque must have at least this many items | minItems keyword |
max_length |
The deque must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only deque instances are valid. Strict mode does not apply to the items of the deque.
The strict constraint must be applied to the parameter type for this to work.
Serialization
In Python mode, deques are serialized as is. In JSON mode, they are serialized as arrays.
Example
from collections import deque
from pydantic import BaseModel
class Model(BaseModel):
deque: deque[int]
print(Model(deque=[1, 2, 3]).deque)
#> deque([1, 2, 3])
Sequences¶
Standard library type: collections.abc.Sequence (deprecated alias: typing.Sequence).
In most cases, you will want to use the built-in types (such as list or tuple) as type coercion
will apply. The Sequence type can be used when you want to preserve the input type during serialization.
Validation
Any collections.abc.Sequence instance (expect strings and bytes) is accepted. It is converted to a list using the list()
constructor, and then converted back to the original input type.
Strings aren't treated as sequences
While strings are technically valid sequence instances, this is frequently not intended as is a common source of bugs.
As a result, Pydantic will not accept strings and bytes for the Sequence type (see example below).
Constraints
Sequences support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The sequence must have at least this many items | minItems keyword |
max_length |
The sequence must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Serialization
In Python mode, sequences are serialized as is. In JSON mode, they are serialized as arrays.
Example
from collections.abc import Sequence
from pydantic import BaseModel, ValidationError
class Model(BaseModel):
sequence_of_strs: Sequence[str]
print(Model(sequence_of_strs=['a', 'bc']).sequence_of_strs)
#> ['a', 'bc']
print(Model(sequence_of_strs=('a', 'bc')).sequence_of_strs)
#> ('a', 'bc')
try:
Model(sequence_of_strs='abc')
except ValidationError as e:
print(e)
"""
1 validation error for Model
sequence_of_strs
'str' instances are not allowed as a Sequence value [type=sequence_str, input_value='abc', input_type=str]
"""
Dictionaries¶
Built-in type: dict.
Validation
dictinstances are accepted as is.- mappings instances are accepted and coerced to a
dict. - If generic parameters for keys and values are provided, the appropriate validation is applied.
Constraints
Dictionaries support the following constraints:
| Constraint | Description | JSON Schema |
|---|---|---|
min_length |
The dictionary must have at least this many items | minItems keyword |
max_length |
The dictionary must have at most this many items | maxItems keyword |
These constraints can be provided using the Field() function.
The MinLen and MaxLen metadata types from the annotated-types
library can also be used.
Strictness
In strict mode, only dict instances are valid. Strict mode does not apply to the keys and values of the dictionaries.
The strict constraint must be applied to the parameter types for this to work.
Example
from pydantic import BaseModel, ValidationError
class Model(BaseModel):
x: dict[str, int]
m = Model(x={'foo': 1})
print(m.model_dump())
#> {'x': {'foo': 1}}
try:
Model(x='test')
except ValidationError as e:
print(e)
"""
1 validation error for Model
x
Input should be a valid dictionary [type=dict_type, input_value='test', input_type=str]
"""
Typed dictionaries¶
Standard library type: typing.TypedDict (see also: the typing specification).
Note
Because of runtime limitations, Pydantic will require using the TypedDict type from
typing_extensions when using Python 3.12 and lower.
TypedDict declares a dictionary type that expects all of its instances to have a certain set of keys
where each key is associated with a value of a consistent type.
This type supports configuration.
Strictness
In strict mode, only dict instances are valid (unlike mappings in lax mode).
Strict mode does not apply to the values of the typed dictionary. The strict constraint must be applied to the value types for this to work.
Example
from typing_extensions import TypedDict
from pydantic import TypeAdapter, ValidationError
class User(TypedDict):
name: str
id: int
ta = TypeAdapter(User)
print(ta.validate_python({'name': 'foo', 'id': 1}))
#> {'name': 'foo', 'id': 1}
try:
ta.validate_python({'name': 'foo'})
except ValidationError as e:
print(e)
"""
1 validation error for User
id
Field required [type=missing, input_value={'name': 'foo'}, input_type=dict]
"""
from typing import TypedDict
from pydantic import TypeAdapter, ValidationError
class User(TypedDict):
name: str
id: int
ta = TypeAdapter(User)
print(ta.validate_python({'name': 'foo', 'id': 1}))
#> {'name': 'foo', 'id': 1}
try:
ta.validate_python({'name': 'foo'})
except ValidationError as e:
print(e)
"""
1 validation error for User
id
Field required [type=missing, input_value={'name': 'foo'}, input_type=dict]
"""
Iterables¶
Standard library type: collections.abc.Iterable (deprecated alias: typing.Iterable).
Validation
Iterables are lazily validated, and wrapped in an internal datastructure that can be iterated over
(and will validated the items type while doing so). This means that even if you provide a concrete
container such as a list, the validated type will not be of type list. However, Pydantic
will ensure that the input value is iterable by getting an iterator from it (by calling
iter() on the value).
It is recommended to use concrete collection types (such as lists) instead, unless you are using an infinite iterator (in which case eagerly validating the input would result in an infinite loop).
Example
from collections.abc import Iterable
from pydantic import BaseModel, ValidationError
class Model(BaseModel):
f: Iterable[str]
m = Model(f=[1, 2]) # Validates fine
try:
next(m.f)
except ValidationError as e:
print(e)
"""
1 validation error for ValidatorIterator
0
Input should be a valid string [type=string_type, input_value=1, input_type=int]
"""
Callable¶
Standard library type: collections.abc.Callable (deprecated alias: typing.Callable).
Validation
Pydantic only validates that the input is a callable (using the callable() function).
It does not validate the number of parameters or their type, nor the type of the return value.
from typing import Callable
from pydantic import BaseModel
class Foo(BaseModel):
callback: Callable[[int], int]
m = Foo(callback=lambda x: x)
print(m)
#> callback=<function <lambda> at 0x0123456789ab>
from collections.abc import Callable
from pydantic import BaseModel
class Foo(BaseModel):
callback: Callable[[int], int]
m = Foo(callback=lambda x: x)
print(m)
#> callback=<function <lambda> at 0x0123456789ab>
Serialization
Callables are serialized as is. Callables can't be serialized in JSON mode
(a PydanticSerializationError is raised).
IP Addresses¶
Standard library types:
ipaddress.IPv4Addressipaddress.IPv4Interfaceipaddress.IPv4Networkipaddress.IPv6Addressipaddress.IPv6Interfaceipaddress.IPv6Network
See also: the IPvAnyAddress, IPvAnyInterface
and IPvAnyNetwork Pydantic types.
Validation
- Instances are validated as is.
- Other input values are passed to the constructor of the relevant address type.
Strictness
In strict mode, only the address types are accepted. In JSON mode, strict mode has no effect.
Serialization
In Python mode, IP addresses are serialized as is. In JSON mode, they are serialized as strings.
UUID¶
Standard library type: uuid.UUID.
Validation
UUIDinstances are validated as is.- Strings and bytes are validated as UUIDs, and casted to a
UUIDinstance.
Constraints
The UUID type supports a version constraint. The UuidVersion metadata type can be used.
Pydantic also provides the following types as convenience aliases: UUID1, UUID3,
UUID4, UUID5, UUID6, UUID7,
UUID8.
Strictness
In strict mode, only UUID instances are accepted.
In JSON mode, strict mode has no effect.
Serialization
In Python mode, UUIDs are serialized as is. In JSON mode, they are serialized as strings.
Example
from typing import Annotated
from uuid import UUID
from pydantic import BaseModel
from pydantic.types import UUID7, UuidVersion
class Model(BaseModel):
u1: UUID7
u2: Annotated[UUID, UuidVersion(4)]
print(
Model(
u1='01999b2c-8353-749b-8dac-859307fae22b',
u2=UUID('125725f3-e1b4-44e3-90c3-1a20eab12da5'),
)
)
"""
u1=UUID('01999b2c-8353-749b-8dac-859307fae22b') u2=UUID('125725f3-e1b4-44e3-90c3-1a20eab12da5')
"""
Type¶
Built-in type: type (deprecated alias: typing.Type).
Validation
Allows any type that is a subclass of the type argument. For instance, with type[str], allows the str
class or any str subclass as an input. If no type argument is provided (i.e. type is used as an annotation),
allow any class.
Serialization
Types are serialized as is. Types can't be serialized in JSON mode
(a PydanticSerializationError is raised).
from pydantic import BaseModel, ValidationError
class Foo:
pass
class Bar(Foo):
pass
class Other:
pass
class SimpleModel(BaseModel):
just_subclasses: type[Foo]
SimpleModel(just_subclasses=Foo)
SimpleModel(just_subclasses=Bar)
try:
SimpleModel(just_subclasses=Other)
except ValidationError as e:
print(e)
"""
1 validation error for SimpleModel
just_subclasses
Input should be a subclass of Foo [type=is_subclass_of, input_value=<class '__main__.Other'>, input_type=type]
"""
Literals¶
Typing construct: typing.Literal (see also: the typing specification).
Literals can be used to only allow specific literal values.
Note that Pydantic applies strict mode behavior when validating literal values (see this issue).
Example
from typing import Literal
from pydantic import BaseModel, ValidationError
class Pie(BaseModel):
flavor: Literal['apple', 'pumpkin']
quantity: Literal[1, 2] = 1
Pie(flavor='apple')
Pie(flavor='pumpkin')
try:
Pie(flavor='cherry')
except ValidationError as e:
print(str(e))
"""
1 validation error for Pie
flavor
Input should be 'apple' or 'pumpkin' [type=literal_error, input_value='cherry', input_type=str]
"""
try:
Pie(flavor='apple', quantity='1')
except ValidationError as e:
print(str(e))
"""
1 validation error for Pie
quantity
Input should be 1 or 2 [type=literal_error, input_value='1', input_type=str]
"""
Any¶
Types: typing.Any or object.
Allows any value, including None.
Hashables¶
Standard library type: collections.abc.Hashable (deprecated alias: typing.Hashable).
Validation
Any value that is hashable (using isinstance(value, Hashable)).
Regex patterns¶
Standard library type: re.Pattern (deprecated alias: typing.Pattern).
Validation
- For
Patterninstances, check that thepatternattribute is of the right type (strorbytesdepending on thePatterntype parameter). - If the type parameter is
strorbytes, input values of typestr(orbytesrespectively) are attempted to be compiled usingre.compile().
Serialization
In Python mode, Pattern instances are
serialized as is.
In JSON mode, they are serialized as strings.
Paths¶
Standard library types:
pathlib.Path.pathlib.PurePath.pathlib.PosixPath.pathlib.PurePosixPath.pathlib.PureWindowsPath.os.PathLike(must be parameterized withstr,bytesorAny).
Validation
- Path instances are validated as is.
- Strings are accepted and passed to the type constructor. If
os.PathLikewas used, bytes are accepted if it was parameterized with thebytestype.
Strictness
In strict mode, only Path instances are accepted. In JSON mode, strict mode has no effect.
Serialization
In Python mode, Path instances are serialized as is.
In JSON mode, they are serialized as strings.