Convert Python datetime to rfc 2822

Question

I want to convert a Python datetime to an RFC 2822 datetime. I've tried these methods to no avail:

>>> from email.Utils import formatdate
>>> import datetime
>>> formatdate(datetime.datetime.now())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/email    /utils.py", line 159, in formatdate
    now = time.gmtime(timeval)
TypeError: a float is required

Answer 1

Here's some working code, broken down into simple pieces just for clarity:

>>> import datetime
>>> import time
>>> from email import utils
>>> nowdt = datetime.datetime.now()
>>> nowtuple = nowdt.timetuple()
>>> nowtimestamp = time.mktime(nowtuple)
>>> utils.formatdate(nowtimestamp)
'Tue, 10 Aug 2010 20:43:53 -0000'

Explanation: email.utils.formatdate wants a timestamp -- i.e., a float with seconds (and fraction thereof) since the epoch. A datetime instance doesn't give you a timestamp directly -- but, it can give you a time-tuple with the timetuple method, and time.mktime of course can then make a timestamp from such a tuple.

EDIT: In Python 3.3 and newer you can do the same in less steps:

>>> import datetime
>>> from email import utils
>>> nowdt = datetime.datetime.now()
>>> utils.format_datetime(nowdt)
'Tue, 10 Feb 2020 10:06:53 -0000'

See format_datetime docs for details on usage.

Answer 2

If you indeed want the current time, just call formatdate with no arguments:

>>> from email.utils import formatdate
>>> formatdate()
'Tue, 10 Aug 2010 20:40:23 -0000'

But, if you must pass it an argument, you want the output of time.time (a number of seconds since 01/01/1970):

>>> import time
>>> formatdate(time.time())
'Tue, 10 Aug 2010 20:41:43 -0000'

FWIW, datetime.datetime.now() returns a datetime object, which is not what formatdate expects.

Edited to add: if you already have a datetime object, you can format it appropriately for formatdate:

>>> import datetime
>>> dt = datetime.datetime.now()
>>> formatdate(float(dt.strftime('%s')))
'Tue, 10 Aug 2010 20:46:16 -0000'

Edited: Alex Martelli noted that the '%s' format string for strftime may not be portable across platforms. A possible alternative would be, as he himself suggested,

>>> formatdate(time.mktime(dt.timetuple()))
'Tue, 10 Aug 2010 20:46:16 -0000'

Answer 3

Python 3.3, in addition to the methods mentioned by other commenters, also added a format_datetime method, which is much cleaner:

>>> import datetime
>>> import email.utils
>>> dt = datetime.datetime.now()
>>> email.utils.format_datetime(dt)
'Thu, 09 Mar 2017 10:50:00 -0000'

Answer 4

Simple method using strftime. Python 2.7. Note: timezone = EST

>>> from datetime import datetime
>>> my_date = datetime.now()
>>> my_date.strftime('%a, %d %b %Y %H:%M:%S -0500')
'Wed, 22 Apr 2020 10:52:11 -0500'

Answer 5

If you're using this for e.g. a HTTP header, and want GMT rather than -0000:

• From a datetime, use format_datetime (emphasis mine):

  If it is an aware timezone with offset zero, then usegmt may be set to True, in which case the string GMT is used instead of the numeric timezone offset.

  >>> from datetime import datetime, timezone
  >>> from email.utils import format_datetime
  >>> format_datetime(datetime.now(timezone.utc), usegmt=True)
  'Wed, 27 Oct 2021 11:00:46 GMT'
  

• From a timestamp, use formatdate:

  Optional usegmt is a flag that when True, outputs a date string with the timezone as an ascii string GMT, rather than a numeric -0000... This only applies when localtime is False.

  >>> from email.utils import formatdate
  >>> from time import time
  >>> formatdate(time(), usegmt=True)
  'Wed, 27 Oct 2021 11:05:29 GMT'