The DuckDBPyType class represents a type instance of our data types.

Converting from Other Types

To make the API as easy to use as possible, we have added implicit conversions from existing type objects to a DuckDBPyType instance. This means that wherever a DuckDBPyType object is expected, it is also possible to provide any of the options listed below.

Python Built-ins

The table below shows the mapping of Python Built-in types to DuckDB type.

Numpy DTypes

The table below shows the mapping of Numpy DType to DuckDB type.

Nested Types

list[child_type]

list type objects map to a LIST type of the child type. Which can also be arbitrarily nested.

import duckdb
from typing import Union

duckdb.typing.DuckDBPyType(list[dict[Union[str, int], str]])

MAP(UNION(u1 VARCHAR, u2 BIGINT), VARCHAR)[]

dict[key_type, value_type]

dict type objects map to a MAP type of the key type and the value type.

import duckdb

print(duckdb.typing.DuckDBPyType(dict[str, int]))

MAP(VARCHAR, BIGINT)

{'a': field_one, 'b': field_two, .., 'n': field_n}

dict objects map to a STRUCT composed of the keys and values of the dict.

import duckdb

print(duckdb.typing.DuckDBPyType({'a': str, 'b': int}))

STRUCT(a VARCHAR, b BIGINT)

Union[⟨type_1⟩, ... ⟨type_n⟩]

typing.Union objects map to a UNION type of the provided types.

import duckdb
from typing import Union

print(duckdb.typing.DuckDBPyType(Union[int, str, bool, bytearray]))

UNION(u1 BIGINT, u2 VARCHAR, u3 BOOLEAN, u4 BLOB)

Creation Functions

For the built-in types, you can use the constants defined in duckdb.typing:

For the complex types there are methods available on the DuckDBPyConnection object or the duckdb module. Anywhere a DuckDBPyType is accepted, we will also accept one of the type objects that can implicitly convert to a DuckDBPyType.

list_type | array_type

Parameters:

• child_type: DuckDBPyType

struct_type | row_type

Parameters:

• fields: Union[list[DuckDBPyType], dict[str, DuckDBPyType]]

map_type

Parameters:

• key_type: DuckDBPyType
• value_type: DuckDBPyType

decimal_type

Parameters:

• width: int
• scale: int

union_type

Parameters:

• members: Union[list[DuckDBPyType], dict[str, DuckDBPyType]]

string_type

Parameters:

• collation: Optional[str]