关于python：如何计算存储在数据库中的两个日期之间的天数？

How do I calculate number of days between two dates stored in a database?

我正在尝试创建一个模块，它从数据库中获取两个不同的日期，创建日期和赢得日期，计算两个日期之间的天数，并将结果存储在一个新字段"比较日期"中。

这是代码：

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def action_set_won(self, cr, uid, ids, context=None):
""" Won semantic: probability = 100 (active untouched)"""
stages_leads = {}
for lead in self.browse(cr, uid, ids, context=context):
stage_id = self.stage_find(cr, uid, [lead], lead.team_id.id or False, [(
'probability', '=', 100.0), ('on_change', '=', True)], context=context)
if stage_id:
if stages_leads.get(stage_id):
stages_leads[stage_id].append(lead.id)
else:
stages_leads[stage_id] = [lead.id]
for stage_id, lead_ids in stages_leads.items():
self.write(cr, uid, lead_ids, {'stage_id': stage_id}, context=context)
return self.write(cr, uid, ids, {'probability': 100, 'won_date': datetime.now(), 'compare_dates': abs('won_date' - 'create_date')}, context=context)

奥多说：

1 2	File"/mnt/extra-addons/crm_updates/models/models.py", line 37, in action_set_won return self.write(cr, uid, ids, {'probability': 100, 'won_date': datetime.now(), 'compare_dates': abs(('won_date') - ('create_date'))}, context=context)

号

类型错误：不支持-："str"和"str"的操作数类型

我知道该怎么做。