ArcPy – Checking if ArcMap is in Edit Session

Question

I've created a Python add-in button that helps speed up my coworkers workflow by copying one feature class attribute to another. It uses the arcpy.UpdateCursor function to update a row in the target feature class. As it exists now, this button script can be run regardless of the editing mode. Obviously when its run in an edit session, the user can choose to stop editing and not save changes, but this is not the case when the script runs outside of an edit session.

How can I add a check to the script that will stop the script from running if ArcMap is not currently in an edit session?

This concerns ArcMap 10 & 10.1

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I also want to check with other ArcMap users to verify that updates to tables is not normally allowed without being in an edit session.

So how is this script running outside of an edit session?

This script also brings up another question about the seemingly serendipitous selection order ArcMap performs that just happens to work for me when I update the 2nd feature class table from a list, but that's for another day.

Here's the script as it works now (without any 10.1 editor implementation):

How to add a check to ensure the user is in an edit session?

def onClick(self):
    #Reference mxd
    mxd = arcpy.mapping.MapDocument("CURRENT")
    #Reference the main Data frame
    mm = arcpy.mapping.ListDataFrames(mxd, "MainMap")[0]
    #Reference the Water System Valve feature class
    waterValves = arcpy.mapping.ListLayers(mxd, "Water System Valve", mm)[0]
    #Reference the fire hydrant feature class
    fireHydrants = arcpy.mapping.ListLayers(mxd, "Water Hydrant", mm)[0]

    #Use the extent of the main DF to select all valves in the current view
    dfAsFeature = arcpy.Polygon(arcpy.Array([mm.extent.lowerLeft, mm.extent.lowerRight, mm.extent.upperRight, mm.extent.upperLeft]), mm.spatialReference)
    arcpy.SelectLayerByLocation_management(waterValves, "WITHIN", dfAsFeature,"", "NEW_SELECTION")

    arcpy.SelectLayerByAttribute_management(waterValves, "SUBSET_SELECTION", "LOCATIONID IS NULL")

    fields = ["LOCATIONID"]

    row, rows = None, None
    rows = arcpy.UpdateCursor(waterValves,fields)
    row = rows.next()
    valveList = []
    append = valveList.append

    #Loop through the valves table to update LocationID
    while row:
        builder = str(row.QSNO)+"-"+ str(row.VALVESEQNO)
        row.setValue("LOCATIONID", builder)
        append(builder)
        rows.updateRow(row)
        row = rows.next()

    del row, rows

    #New selection for fire hydrants
    arcpy.SelectLayerByLocation_management(fireHydrants, "WITHIN", dfAsFeature,"", "NEW_SELECTION")
    arcpy.SelectLayerByAttribute_management(fireHydrants, "SUBSET_SELECTION", "LOCATIONID IS NULL")

    row, rows = None, None
    rows = arcpy.UpdateCursor(fireHydrants,fields)
    row = rows.next()

    #Loop through fire hydrant table to update LocationID
    while row:
        for locID in valveList:
            construct = str(locID) + "-FH"
            #print construct
            row.setValue("LOCATIONID", construct)
            rows.updateRow(row)
            row = rows.next()

    del row, rows, valveList, mxd

Answer 1

Here's a generic function based on this post.

Maybe this is a little more kludgy than the ArcObjects solution, but it sure seems like a lot less hassle! Simple is better than complex. Except when it isn't.

Example usage:

if CheckEditSession(tbl):
    print("An edit session is currently open.")

code:

def CheckEditSession(lyr):
    """Check for an active edit session on an fc or table.
    Return True of edit session active, else False"""
    edit_session = True
    row1 = None
    try:
        # attempt to open two cursors on the input
        # this generates a RuntimeError if no edit session is active
        OID = arcpy.Describe(lyr).OIDFieldName
        with arcpy.da.UpdateCursor(lyr, OID) as rows:
            row = next(rows)
            with arcpy.da.UpdateCursor(lyr, OID) as rows2:
                row2 = next(rows2)
    except RuntimeError as e:
        if e.message == "workspace already in transaction mode":
            # this error means that no edit session is active
            edit_session = False
        else:
            # we have some other error going on, report it
            raise
    return edit_session