Converting between Javascript date and Python datetime with bson

gistfile1.txt

from bson.tz_util import utc
from datetime import datetime, timedelta

# This file is to impliment date related helper functions
#
# This is mainly needed because bson uses the javascript date class.
# The javascript Date() class represents timestamps in milliseconds.
# For some documentation on how Bson, Json, and Date work together, refer to:
# http://blog.mongohq.com/from-json-to-bson-and-back/
#
# The python datetime class represents timestamps in seconds.
#
# Furthermore, the python bson class uses its own time zone.
# What this means is that uses datetime.utcfromtimestamp alone is not enough.
# This is because utcfromtimestamp will represent the time zone as None.
# You also can't create your own UTC class, because the datetime comparator
# just checks that the time zone object is of the same ID.
#
# You must use datetime.fromtimestamp(<timestamp>, <tz>)
# Where <timestamp> is the converted timestamp, and <tz> is bson.tz_util.utc

# Precondition: timestamp represented in milliseconds
#               timestamp could be either a string or integer
# Returns: DateTime object representing the timestamp given
#
# Possible ToDo: Allow an optional time zone parameter


def bsonToDateTime(timestamp):
    # Make sure we are dealing with an integer. If not convert it.
    timestamp = int(timestamp)

    # Save the milliseconds so they aren't lost in conversion
    # due to datetime.fromtimestamp only being as precise as seconds
    milliseconds = timestamp % 1000

    timestampInSeconds = timestamp / 1000
    time = datetime.fromtimestamp(timestampInSeconds, utc)

    # convert our milliseconds to microseconds so we can store it in our
    # new datetime object to the correct precision
    time = time + timedelta(0, 0, 0, milliseconds)

    return time

# Precondition: timestamp represented in milliseconds
#               timestamp could be either a string or integer
# Returns: DateTime object representing the timestamp given


def dateTimeToBson(dateTimeObject):
    # Find the time delta since the epoch

    epoch = dateTimeEpoch()
    delta = dateTimeObject - epoch

    # 60 seconds   60 minutes   24 hours     86400 seconds
    # ---------- * ---------- * ---------- = --------------
    # 1 minutes    1 hour       1 day        1 day

    secondsInDay = 86400
    deltaDaysInSeconds = delta.days * secondsInDay
    deltaSeconds = delta.seconds
    totalSeconds = deltaDaysInSeconds + deltaSeconds

    # 1000 milliseconds
    # -----------------
    # 1 second

    totalSecondsToMilliseconds = totalSeconds * 1000

    # 1000 microseconds
    # -----------------
    #  1 millisecond

    deltaMilliseconds = delta.microseconds/1000
    totalMilliseconds = totalSecondsToMilliseconds + deltaMilliseconds

    return totalMilliseconds


def dateTimeEpoch():
    return datetime.fromtimestamp(0, utc)


def now():
    currentDateTime = datetime.utcnow()

    # Use division to round down to correct precision
    # Use multiplication to replace the lost zeros
    millisecondsRoundedDown = currentDateTime.microsecond/1000*1000

    return currentDateTime.replace(tzinfo=utc, microsecond=millisecondsRoundedDown)