Not sure if you are using or talking about Field Calculator. If so, the short answer to your question is, "no." There is no way using Python with the Field Calculator to emulate the Arcade code for counting attachments. Outside of Field Calculator, the answer to your question is, "not really." That is, the ArcPy way of updating a field to reflect the attachment count isn't what most people would consider 'simple,' although it is quite possible.
The following code snippet should work:
import arcpy
import os
import warnings
from collections import defaultdict
table = # path to table
attach_count_field = # field for holding count of attachments
dcn = []
desc = arcpy.Describe(table)
for name in desc.relationshipClassNames:
rel = arcpy.Describe(os.path.join(desc.path, name))
if rel.isAttachmentRelationship:
dcn = rel.destinationClassNames
if not dcn:
warnings.warn("Table '{}' does not have attachments enabled".format(table))
attach_count = defaultdict(int)
for name in dcn:
with arcpy.da.SearchCursor(os.path.join(desc.path, name), "REL_OBJECTID") as cur:
for rel_oid, in cur:
attach_count[rel_oid] += 1
with arcpy.da.UpdateCursor(table, ["OID@", attach_count_field]) as cur:
for oid, _ in cur:
cur.updateRow([oid, attach_count[oid] if dcn else None])
If a table had attachments and they were removed/disabled, the code will set the count field to NULL to reflect attachments are not enabled.
