Попробуйте следующий код:
result_gantt = [{"id":1,"prj_id":808348,"parent":1},{"id":2,"prj_id":808352,"parent":2},{"id":3,"prj_id":808356,"parent":3},{"id":4,"prj_id":808361,"parent":4},{"id":5,"prj_id":808365,"parent":0},{"id":6,"prj_id":808370,"parent":0},{"id":7,"prj_id":808370,"parent":6},{"id":8,"prj_id":808370,"parent":7},{"id":9,"prj_id":808370,"parent":8}]
index = 0
prev_index = 0 # To maintain the index in case of consecutive id's
last_prj_id = ""
check = False # Check for consecutive id's
for row in result_gantt:
current_prj_id = row['prj_id']
parent = row['parent']
parent = index
if current_prj_id == last_prj_id:
if not check: # Will be true in case of consecutive id's
prev_index = last_id
parent = last_id
check = True
else:
check = False
parent = index
last_prj_id = row['prj_id']
last_id = row['id']
row['parent'] = parent if not check else prev_index
for i in result_gantt:
print i
Выход:
{'prj_id': 808348, 'id': 1, 'parent': 0}
{'prj_id': 808352, 'id': 2, 'parent': 0}
{'prj_id': 808356, 'id': 3, 'parent': 0}
{'prj_id': 808361, 'id': 4, 'parent': 0}
{'prj_id': 808365, 'id': 5, 'parent': 0}
{'prj_id': 808370, 'id': 6, 'parent': 0}
{'prj_id': 808370, 'id': 7, 'parent': 6}
{'prj_id': 808370, 'id': 8, 'parent': 6}
{'prj_id': 808370, 'id': 9, 'parent': 6}