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Added docs for the Column object
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Daniele Varrazzo
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3
NEWS
3
NEWS
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@ -7,6 +7,9 @@ What's new in psycopg 2.8
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New features:
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- Added `~psycopg2.extensions.encrypt_password()` function (:ticket:`#576`).
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- Added `~psycopg2.extensions.Column.table_oid` and
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`~psycopg2.extensions.Column.table_column` attributes on `cursor.description`
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items (:ticket:`#661`).
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- Added `connection.host` property (:ticket:`#726`).
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- `~psycopg2.sql.Identifier` can represent qualified names in SQL composition
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(:ticket:`#732`).
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@ -37,46 +37,49 @@ The ``cursor`` class
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.. attribute:: description
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This read-only attribute is a sequence of 7-item sequences.
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Read-only attribute describing the result of a query. It is a
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sequence of `~psycopg2.extensions.Column` instances, each one
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describing one result column in order. The attribute is `!None` for
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operations that do not return rows or if the cursor has not had an
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operation invoked via the |execute*|_ methods yet.
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Each of these sequences is a named tuple (a regular tuple if
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:func:`collections.namedtuple` is not available) containing information
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describing one result column:
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For compatibility with the DB-API, every object can be unpacked as a
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7-items sequence: the attributes retuned this way are the following.
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For further details and other attributes available check the
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`~psycopg2.extensions.Column` documentation.
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0. `!name`: the name of the column returned.
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1. `!type_code`: the PostgreSQL OID of the column. You can use the
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|pg_type|_ system table to get more informations about the type.
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This is the value used by Psycopg to decide what Python type use
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to represent the value. See also
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:ref:`type-casting-from-sql-to-python`.
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2. `!display_size`: the actual length of the column in bytes.
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Obtaining this value is computationally intensive, so it is
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always `!None` unless the :envvar:`PSYCOPG_DISPLAY_SIZE` parameter
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is set at compile time. See also PQgetlength_.
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3. `!internal_size`: the size in bytes of the column associated to
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this column on the server. Set to a negative value for
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variable-size types See also PQfsize_.
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4. `!precision`: total number of significant digits in columns of
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type |NUMERIC|_. `!None` for other types.
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5. `!scale`: count of decimal digits in the fractional part in
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columns of type |NUMERIC|. `!None` for other types.
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6. `!null_ok`: always `!None` as not easy to retrieve from the libpq.
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0. `~psycopg2.extensions.Column.name`: the name of the column returned.
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This attribute will be `!None` for operations that do not return rows
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or if the cursor has not had an operation invoked via the
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|execute*|_ methods yet.
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1. `~psycopg2.extensions.Column.type_code`: the PostgreSQL OID of the
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column.
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.. |pg_type| replace:: :sql:`pg_type`
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.. _pg_type: https://www.postgresql.org/docs/current/static/catalog-pg-type.html
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.. _PQgetlength: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQGETLENGTH
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.. _PQfsize: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQFSIZE
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.. _NUMERIC: https://www.postgresql.org/docs/current/static/datatype-numeric.html#DATATYPE-NUMERIC-DECIMAL
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.. |NUMERIC| replace:: :sql:`NUMERIC`
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2. `~psycopg2.extensions.Column.display_size`: the actual length of
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the column in bytes.
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3. `~psycopg2.extensions.Column.internal_size`: the size in bytes of
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the column associated to this column on the server.
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4. `~psycopg2.extensions.Column.precision`: total number of
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significant digits in columns of type |NUMERIC|. `!None`
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for other types.
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5. `~psycopg2.extensions.Column.scale`: count of decimal digits in
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the fractional part in columns of type |NUMERIC|. `!None`
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for other types.
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6. `~psycopg2.extensions.Column.null_ok`: always `!None` as not easy
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to retrieve from the libpq.
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.. versionchanged:: 2.4
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if possible, columns descriptions are named tuple instead of
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regular tuples.
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.. versionchanged:: 2.8
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columns descriptions are instances of `!Column`, exposing extra
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attributes.
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.. |NUMERIC| replace:: :sql:`NUMERIC`
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.. method:: close()
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Close the cursor now (rather than whenever `del` is executed).
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@ -154,6 +154,80 @@ introspection etc.
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Close the object and remove it from the database.
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.. class:: Column
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Description of one result column, exposed as items of the
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`cursor.description` sequence.
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.. versionadded:: 2.8
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in previous version the `!description` attribute was a sequence of
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simple tuples or namedtuples.
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.. attribute:: name
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The name of the column returned.
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.. attribute:: type_code
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The PostgreSQL OID of the column. You can use the |pg_type|_ system
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table to get more informations about the type. This is the value used
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by Psycopg to decide what Python type use to represent the value. See
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also :ref:`type-casting-from-sql-to-python`.
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.. attribute:: display_size
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The actual length of the column in bytes. Obtaining this value is
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computationally intensive, so it is always `!None` unless the
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:envvar:`PSYCOPG_DISPLAY_SIZE` parameter is set at compile time. See
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also PQgetlength_.
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.. attribute:: internal_size
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The size in bytes of the column associated to this column on the
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server. Set to a negative value for variable-size types See also
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PQfsize_.
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.. attribute:: precision
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Total number of significant digits in columns of type |NUMERIC|_.
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`!None` for other types.
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.. attribute:: scale
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Count of decimal digits in the fractional part in columns of type
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|NUMERIC|. `!None` for other types.
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.. attribute:: null_ok
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Always `!None` as not easy to retrieve from the libpq.
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.. attribute:: table_oid
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The oid of the table from which the column was fetched (matching
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:sql:`pg_class.oid`). `!None` if the column is not a simple reference
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to a table column. See also PQftable_.
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.. versionadded:: 2.8
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.. attribute:: table_column
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The number of the column (within its table) making up the result
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(matching :sql:`pg_attribute.attnum`, so it will start from 1).
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`!None` if the column is not a simple reference to a table column. See
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also PQftablecol_.
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.. versionadded:: 2.8
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.. |pg_type| replace:: :sql:`pg_type`
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.. _pg_type: https://www.postgresql.org/docs/current/static/catalog-pg-type.html
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.. _PQgetlength: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQGETLENGTH
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.. _PQfsize: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQFSIZE
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.. _PQftable: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQFTABLE
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.. _PQftablecol: https://www.postgresql.org/docs/current/static/libpq-exec.html#LIBPQ-PQFTABLECOL
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.. _NUMERIC: https://www.postgresql.org/docs/current/static/datatype-numeric.html#DATATYPE-NUMERIC-DECIMAL
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.. |NUMERIC| replace:: :sql:`NUMERIC`
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.. autoclass:: Notify(pid, channel, payload='')
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:members: pid, channel, payload
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