Class Column

source code

     object --+            
              |            
 ligolw.Element --+        
                  |        
ligolw.EmptyElement --+    
                      |    
          ligolw.Column --+
                          |
                         Column

High-level column element that provides list-like access to the values in a column.

Example:

>>> from xml.sax.xmlreader import AttributesImpl
>>> import sys
>>> tbl = Table(AttributesImpl({u"Name": u"test"}))
>>> col = tbl.appendChild(Column(AttributesImpl({u"Name": u"test:snr", u"Type": u"real_8"})))
>>> tbl.appendChild(TableStream(AttributesImpl({u"Name": u"test"})))    # doctest: +ELLIPSIS
<glue.ligolw.table.TableStream object at ...>
>>> tbl._update_column_info()
>>> col.Name
u'snr'
>>> col.Type
u'real_8'
>>> # append 3 rows (with nothing in them)
>>> tbl.append(tbl.RowType())
>>> tbl.append(tbl.RowType())
>>> tbl.append(tbl.RowType())
>>> # assign values to the rows, in order, in this column
>>> col[:] = [8.0, 10.0, 12.0]
>>> col[:]
[8.0, 10.0, 12.0]
>>> col.asarray()
array([  8.,  10.,  12.])
>>> tbl.write(sys.stdout)       # doctest: +NORMALIZE_WHITESPACE
<Table Name="test">
        <Column Type="real_8" Name="test:snr"/>
        <Stream Name="test">
                8,
                10,
                12
        </Stream>
</Table>
>>> col.index(10)
1
>>> 12 in col
True
>>> col[0] = 9.
>>> col[1] = 9.
>>> col[2] = 9.
>>> tbl.write(sys.stdout)               # doctest: +NORMALIZE_WHITESPACE
<Table Name="test">
        <Column Type="real_8" Name="test:snr"/>
        <Stream Name="test">
                9,
                9,
                9
        </Stream>
</Table>
>>> col.count(9)
3

NOTE: the .Name attribute returns the stripped "Name" attribute of the element, e.g. with the table suffix removed, but when assigning to the .Name attribute the value provided is stored without modification, i.e. there is no attempt to reattach the table's name to the string. The calling code is responsible for doing the correct manipulations. Therefore, the assignment operation below

>>> col.Name, col.getAttribute("Name")
(u'snr', u'test:snr')
>>> col.Name = col.Name
>>> col.Name, col.getAttribute("Name")
(u'snr', u'snr')

does not preserve the value of the "Name" attribute (though it does preserve the stripped form reported by the .Name property). This asymmetry is necessary because the correct table name string to reattach to the attribute's value cannot always be known, e.g., if the Column object is not part of an XML tree and does not have a parent node.