为什么 datetime.now(datetime.timezone.utc) 和 datetime.datetime.utcnow() 之间的区别

Question

如果你调用 datetime.datetime.now(datetime.timezone.utc) 你会得到类似 datetime.datetime(2021, 9, 8, 1, 33, 19, 684253, tzinfo=datetime.timezone.utc).

的结果

如果你调用 datetime.datetime.utcnow()，你会得到类似 datetime.datetime(2021, 9, 8, 1, 33, 20, 283212) 的结果。

结果似乎相同，但实际上并非如此，因为 时间戳 会有所不同。例如。调用 datetime.datetime.now(datetime.timezone.utc).timestamp() - datetime.datetime.utcnow().timestamp() returns（对我来说）：-18000.000012159348.

这是为什么？

import datetime

print()
print(datetime.datetime.now(datetime.timezone.utc))
print(datetime.datetime.utcnow())

print()
print(datetime.datetime.now(datetime.timezone.utc).timestamp())
print(datetime.datetime.utcnow().timestamp())
print(datetime.datetime.now(datetime.timezone.utc).timestamp() - datetime.datetime.utcnow().timestamp())

Answer 1

utcnow 创建一个简单的 datetime 实例，因为在 Python 中引入时没有 UTC 时区对象。来自 timestamp() 的文档：

Naive datetime instances are assumed to represent local time and this method relies on the platform C mktime() function to perform the conversion.

Answer 2

此行为已记录在案。发生这种情况是因为 utcnow() returns 天真的日期时间。

datetime.utcnow()

Return the current UTC date and time, with tzinfo None.

This is like now(), but returns the current UTC date and time, as a naive datetime object. An aware current UTC datetime can be obtained by calling datetime.now(timezone.utc).

这就是为什么文档还说 datetime.now()

This function is preferred over today() and utcnow().

为什么 datetime.now(datetime.timezone.utc) 和 datetime.datetime.utcnow() 之间的区别

Why the difference between datetime.now(datetime.timezone.utc) and datetime.datetime.utcnow()

python

datetime

python-datetime