# Type – Type objects and constructors

## Type constructors

For binding to an operation’s input parameters, PostgreSQL needs to have the input in a particular format. However, from the parameters to the `Cursor.execute()` and `Cursor.executemany()` methods it is not always obvious as which PostgreSQL data types they shall be bound. For instance, a Python string could be bound as a simple `char` value, or also as a `date` or a `time`. Or a list could be bound as a `array` or a `json` object. To make the intention clear in such cases, you can wrap the parameters in type helper objects. PyGreSQL provides the constructors defined below to create such objects that can hold special values. When passed to the cursor methods, PyGreSQL can then detect the proper type of the input parameter and bind it accordingly.

The `pgdb` module exports the following type constructors as part of the DB-API 2 standard:

`pgdb.``Date`(year, month, day)

  Construct an object holding a date value

`pgdb.``Time`(hour[, minute][, second][, microsecond][, tzinfo])

  Construct an object holding a time value

`pgdb.``Timestamp`(year, month, day[, hour][, minute][, second][, microsecond][, tzinfo])

  Construct an object holding a time stamp value

`pgdb.``DateFromTicks`(ticks)

  Construct an object holding a date value from the given ticks value

`pgdb.``TimeFromTicks`(ticks)

  Construct an object holding a time value from the given ticks value

`pgdb.``TimestampFromTicks`(ticks)

  Construct an object holding a time stamp from the given ticks value

`pgdb.``Binary`(bytes)

  Construct an object capable of holding a (long) binary string value

Additionally, PyGreSQL provides the following constructors for PostgreSQL specific data types:

`pgdb.``Interval`(days, hours=0, minutes=0, seconds=0, microseconds=0)

  Construct an object holding a time interval value

New in version 5.0.

`pgdb.``Uuid`([hex][, bytes][, bytes_le][, fields][, int][, version])

  Construct an object holding a UUID value

New in version 5.0.

`pgdb.``Hstore`(dict)

  Construct a wrapper for holding an hstore dictionary

New in version 5.0.

`pgdb.``Json`(obj[, encode])

  Construct a wrapper for holding an object serializable to JSON

  You can pass an optional serialization function as a parameter. By default, PyGreSQL uses `json.dumps()` to serialize it.

`pgdb.``Literal`(sql)

  Construct a wrapper for holding a literal SQL string

New in version 5.0.

Example for using a type constructor:

    >>> cursor.execute("create table jsondata (data jsonb)")
    >>> data = {'id': 1, 'name': 'John Doe', 'kids': ['Johnnie', 'Janie']}
    >>> cursor.execute("insert into jsondata values (%s)", [Json(data)])

Note

SQL `NULL` values are always represented by the Python None singleton on input and output.

## Type objects

class `pgdb.``Type`

The `Cursor.description` attribute returns information about each of the result columns of a query. The type_code must compare equal to one of the `Type` objects defined below. Type objects can be equal to more than one type code (e.g. `DATETIME` is equal to the type codes for `date`, `time` and `timestamp` columns).

The pgdb module exports the following `Type` objects as part of the DB-API 2 standard:

`STRING`

  Used to describe columns that are string-based (e.g. `char`, `varchar`, `text`)

`BINARY`

  Used to describe (long) binary columns (`bytea`)

`NUMBER`

  Used to describe numeric columns (e.g. `int`, `float`, `numeric`, `money`)

`DATETIME`

  Used to describe date/time columns (e.g. `date`, `time`, `timestamp`, `interval`)

`ROWID`

  Used to describe the `oid` column of PostgreSQL database tables

Note

The following more specific type objects are not part of the DB-API 2 standard.

`BOOL`

  Used to describe `boolean` columns

`SMALLINT`

  Used to describe `smallint` columns

`INTEGER`

  Used to describe `integer` columns

`LONG`

  Used to describe `bigint` columns

`FLOAT`

  Used to describe `float` columns

`NUMERIC`

  Used to describe `numeric` columns

`MONEY`

  Used to describe `money` columns

`DATE`

  Used to describe `date` columns

`TIME`

  Used to describe `time` columns

`TIMESTAMP`

  Used to describe `timestamp` columns

`INTERVAL`

  Used to describe date and time `interval` columns

`UUID`

  Used to describe `uuid` columns

`HSTORE`

  Used to describe `hstore` columns

New in version 5.0.

`JSON`

  Used to describe `json` and `jsonb` columns

New in version 5.0.

`ARRAY`

  Used to describe columns containing PostgreSQL arrays

New in version 5.0.

`RECORD`

  Used to describe columns containing PostgreSQL records

New in version 5.0.

Example for using some type objects:

    >>> cursor = con.cursor()
    >>> cursor.execute("create table jsondata (created date, data jsonb)")
    >>> cursor.execute("select * from jsondata")
    >>> (created, data) = (d.type_code for d in cursor.description)
    >>> created == DATE
    True
    >>> created == DATETIME
    True
    >>> created == TIME
    False
    >>> data == JSON
    True
    >>> data == STRING
    False