Converting a formatted time string to milliseconds

Question

I am trying to convert '2015-09-15T17:13:29.380Z' to milliseconds.

At first I used:

time.mktime(
  datetime.datetime.strptime(
    "2015-09-15T17:13:29.380Z",
    "%Y-%m-%dT%H:%M:%S.%fZ"
  ).timetuple()
)

I got 1442330009.0 - with no microseconds. I think time.mktime rounds the number to the nearest second.

In the end I did:

origTime = '2015-09-15T17:13:29.380Z'
tupleTime = datetime.datetime.strptime(origTime, "%Y-%m-%dT%H:%M:%S.%fZ")
microsecond = tupleTime.microsecond
updated = float(time.mktime(tupleTime.timetuple())) + (microsecond * 0.000001)

Is there a better way to do this and how do I work with the timezone?

Solution 1

Your input time is in UTC; it is incorrect to use time.mktime() here unless your local timezone is always UTC.

There are two steps:

1. Convert the input rfc 3339 time string into a datetime object that represents time in UTC

   from datetime import datetime
   
   utc_time = datetime.strptime("2015-09-15T17:13:29.380Z",
                                "%Y-%m-%dT%H:%M:%S.%fZ")
   

   You've already done it. See also Convert an RFC 3339 time to a standard Python timestamp

2. Convert UTC time to POSIX time expressed in milliseconds:

   from datetime import datetime, timedelta
   
   milliseconds = (utc_time - datetime(1970, 1, 1)) // timedelta(milliseconds=1)
   # -> 1442337209380
   

   For a version that works on Python 2.6-3+, see How can I convert a datetime object to milliseconds since epoch (unix time) in Python?

Solution 2

Unfortunately, there is no miliseconds in timetuple. However, you don't need timetuple. For timestamp, just call

datetime.strptime(...).timestamp()

As for timezone, check out tzinfo argument of datetime.

EDIT: tzinfo

>>> d
datetime.datetime(2015, 9, 15, 17, 13, 29, 380000)
>>> d.timestamp()
1442330009.38
>>> import pytz
>>> d.replace(tzinfo=pytz.timezone("US/Eastern")).timestamp()
1442355209.38