Class Table

tables/table.py:384–3241

This class represents heterogeneous datasets in an HDF5 file. Tables are leaves (see the Leaf class in :ref:`LeafClassDescr`) whose data consists of a unidimensional sequence of *rows*, where each row contains one or more *fields*. Fields have an associated unique *name* and *posit

class Table(tableextension.Table, Leaf):
    """This class represents heterogeneous datasets in an HDF5 file.

    Tables are leaves (see the Leaf class in :ref:`LeafClassDescr`) whose data
    consists of a unidimensional sequence of *rows*, where each row contains
    one or more *fields*.  Fields have an associated unique *name* and
    *position*, with the first field having position 0.  All rows have the same
    fields, which are arranged in *columns*.

    Fields can have any type supported by the Col class (see
    :ref:`ColClassDescr`) and its descendants, which support multidimensional
    data.  Moreover, a field can be *nested* (to an arbitrary depth), meaning
    that it includes further fields inside.  A field named x inside a nested
    field a in a table can be accessed as the field a/x (its *path name*) from
    the table.

    The structure of a table is declared by its description, which is made
    available in the Table.description attribute (see :class:`Table`).

    This class provides new methods to read, write and search table data
    efficiently.  It also provides special Python methods to allow accessing
    the table as a normal sequence or array (with extended slicing supported).

    PyTables supports *in-kernel* searches working simultaneously on several
    columns using complex conditions.  These are faster than selections using
    Python expressions.  See the :meth:`Table.where` method for more
    information on in-kernel searches.

    Non-nested columns can be *indexed*.  Searching an indexed column can be
    several times faster than searching a non-nested one.  Search methods
    automatically take advantage of indexing where available.

    When iterating a table, an object from the Row (see :ref:`RowClassDescr`)
    class is used.  This object allows to read and write data one row at a
    time, as well as to perform queries which are not supported by in-kernel
    syntax (at a much lower speed, of course).

    Objects of this class support access to individual columns via *natural
    naming* through the :attr:`Table.cols` accessor.  Nested columns are
    mapped to Cols instances, and non-nested ones to Column instances.
    See the Column class in :ref:`ColumnClassDescr` for examples of this
    feature.

    Parameters
    ----------
    parentnode
        The parent :class:`Group` object.

        .. versionchanged:: 3.0
           Renamed from *parentNode* to *parentnode*.

    name : str
        The name of this node in its parent group.
    description
        An IsDescription subclass or a dictionary where the keys are the field
        names, and the values the type definitions. In addition, a pure NumPy
        dtype is accepted.  If None, the table metadata is read from disk,
        else, it's taken from previous parameters.