introspection.py.txt

"""
loop through QGIS layers and list some properties for introspection
helps to audit available data and identify possible underlying issues
and it's easy to add additional attributes from layers to the output

designed to be copy pasted into the python console within a QGIS project
"""

# if you want to run from pyhon directly, you must first import the relevant libraries.
# from the QGIS pyhon console, you will need to import system libraries where needed (e.g. import os)

layers = [layer for layer in QgsProject.instance().mapLayers().values()]  # Get a list of all map layers
# layers = QgsProject.instance().mapLayersByName('layer_name')  # get a layers by name
# layer = layers[0]  # get the first object in the layers list
# layer = iface.activeLayer()  # get currently active layer (last selected if multiple)

# To list available attributes and methods, you can use the python dir command
# layer.__dir__()  # same as dir(layer)
# for i in layer.__dir__():
#     print(i)
# careful though, as there are over 500 for qgis layers
# alternatively use the api docs at https://qgis.org/pyqgis

"""
itemCalc fields are added for placeholding expected spreadsheet formula.
this is expected to be manual as there may exist a variety of data sources
assuming default configuration and column settings, the following should apply:

serviceCalc: =MID(LEFT(E2,FIND("' sslmode",E2)),FIND("service='",E2), LEN(E2))
if there's an error, you can try =MID(LEFT(E2,FIND("' key",E2)),FIND("service='",E2), LEN(E2))

tableCalc: =MID(LEFT(E2,FIND(" (",E2)-1),FIND("table=",E2), LEN(E2))
geomCalc: =MID(LEFT(E2,FIND(")",E2)-1),FIND("(",E2)+1, LEN(E2))
crsCalc: =MID(LEFT(H2,FIND(">",H2)-1),FIND("EPSG:",H2), LEN(H2))
"""

# output_file = 'C:\\Path\\output_list.txt'  # Windows path
output_file = '~/path/output_list.txt'  # Linux path

with open(output_file, 'w') as f:  # write file headers
    print('name|serviceCalc|tableCalc|geomCalc|source|filter|crsCalc|sourceCrs|featureCount|xmax|ymax|xmin|ymin', file=f)

outputCrs = QgsCoordinateReferenceSystem('EPSG:4326')

for layer in layers:  # iterate over layers list. Result is | delimited output
    try:  # basic error handling
        if layer.type() == QgsMapLayer.VectorLayer:  # skip if data type != vector
            # We will transform the bounding extents to the project crs to identify anything out of place
            # we can't compare across different CRS systems because it's apples to oranges
            transform = QgsCoordinateTransform(layer.sourceCrs(), outputCrs, QgsProject.instance())
            extent = transform.transformBoundingBox(layer.extent())  # layer extent in source coords
            xmax = extent.xMaximum()
            ymax = extent.yMaximum()
            xmin = extent.xMinimum()
            ymin = extent.yMinimum()
            # print('{0}||||{1}|{2}||{3}|{4}|{5}|{6}|{7}|{8}'.format(layer.name(), layer.source(), layer.subsetString(),
            #       layer.sourceCrs(), layer.featureCount(), xmax, ymax, xmin, ymin))  # use this to print to the console only
            with open(output_file, 'a+') as f:  # use this to append to the output file
                print('Adding {0}'.format(layer.name()))  # Print the current layer name to console
                print('{0}||||{1}|{2}||{3}|{4}|{5}|{6}|{7}|{8}'.format(layer.name(), layer.source(), layer.subsetString(),
                      layer.sourceCrs(), layer.featureCount(), xmax, ymax, xmin, ymin), file=f)  # Write out attributes to file
        else:
            print('Skipping non-vector layer {0}'.format(layer.name()))
    except Exception as err:
        print(str(err))

print('done...')  # let yourself know it's finished