为什么我不能加strptime，只做减法呢？

Question

这可以很好地工作：

{{ strptime(states('input_datetime.music_alarm'), "%H:%M:%S") - strptime("10", "%M") }} 

但这会抛出一个错误：

{{ strptime(states('input_datetime.music_alarm'), "%H:%M:%S") + strptime("10", "%M") }} 

states('input_datetime.music_alarm')等于一个时间，如08:00:00

我在用jinja2做家政助理。这就是错误。

Error doing job: Task exception was never retrieved
Traceback (most recent call last):
  File "/usr/lib/python3.5/asyncio/tasks.py", line 239, in _step
    result = coro.send(None)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/automation/__init__.py", line 336, in async_trigger
    yield from self._async_action(self.entity_id, variables)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/components/automation/__init__.py", line 425, in action
    yield from script_obj.async_run(variables)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/script.py", line 158, in async_run
    await self._async_call_service(action, variables)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/script.py", line 187, in _async_call_service
    self.hass, action, True, variables, validate_config=False)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/service.py", line 72, in async_call_from_config
    config[CONF_SERVICE_DATA_TEMPLATE], variables))
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/template.py", line 56, in render_complex
    for key, item in value.items()}
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/template.py", line 56, in <dictcomp>
    for key, item in value.items()}
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/template.py", line 57, in render_complex
    return value.async_render(variables)
  File "/srv/homeassistant/lib/python3.5/site-packages/homeassistant/helpers/template.py", line 132, in async_render
    return self._compiled.render(kwargs).strip()
  File "/srv/homeassistant/lib/python3.5/site-packages/jinja2/environment.py", line 1008, in render
    return self.environment.handle_exception(exc_info, True)
  File "/srv/homeassistant/lib/python3.5/site-packages/jinja2/environment.py", line 780, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/srv/homeassistant/lib/python3.5/site-packages/jinja2/_compat.py", line 37, in reraise
    raise value.with_traceback(tb)
  File "<template>", line 1, in top-level template code
TypeError: bad operand type for unary -: 'datetime.datetime'

Answer 1

您必须使用timedelta，并且您的代码中存在多个问题。

1/错误使用datetime.datetime.strptime()

>>> import datetime
>>> print(datetime.datetime.strptime("10", "%M"))
1900-01-01 00:10:00
>>> print(datetime.datetime.strptime('08:00:00', "%H:%M:%S"))
1900-01-01 08:00:00

您必须解析完整的datetime才能拥有正确的行为。

2/不能将两个日期时间相加

基本上，为了避免错误，+是被禁止的，你只需要-，因为你只需要颠倒表达式中的变量，就可以得到负的时间增量。

>>> print(type(datetime.datetime.strptime("10", "%M") - datetime.datetime.strptime('08:00:00', "%H:%M:%S")))
<class 'datetime.timedelta'>
>>> print(datetime.datetime.strptime("10", "%M") - datetime.datetime.strptime('08:00:00', "%H:%M:%S"))
-1 day, 16:10:00
>>> print(datetime.datetime.strptime('08:00:00', "%H:%M:%S") - datetime.datetime.strptime("10", "%M"))
7:50:00

你可以看到相反的顺序，这会给你不正确的-1 day, 16:10:00，因为这不能没有错误地处理。

3/您可以将timedelta注册到您的模板

在Jinja2中，strptime()在默认情况下是不可用的，所以请使用TimeDelta...

大概是这样的：

import datetime
from jinja2 import Template

jinga = Template('{{ strptime(states("input_datetime.music_alarm"), "%H:%M:%S") - timedelta(minutes=10) }} ')
jinga.globals['timedelta'] = datetime.timedelta
print(jinga.render())