First, you'll have to get the ID of the row that contains this window construction.
For this example, assume that the name of the window construction in the IDF is Window Cons A
Note the window construction name must be all uppercase in the query, even if not uppercase in the IDF.
row_id = "SELECT RowName
FROM tabulardatawithstrings
WHERE ReportName='EnvelopeSummary'
AND ReportForString='Entire Facility'
AND TableName='Exterior Fenestration'
AND Value='WINDOW CONS A'"
Next, get the SHGC using the row ID
shgc = "SELECT Value
FROM tabulardatawithstrings
WHERE ReportName='EnvelopeSummary'
AND ReportForString='Entire Facility'
AND TableName='Exterior Fenestration'
AND ColumnName='Glass SHGC'
AND RowName=row_id"
You can replace Glass SHGC
with Glass Visible Transmittance
or Glass U-Factor
in the second query to get these other properties too.