Python datetime to Matlab datenum

Question

How do you convert a Python datetime to a Matlab datetnum?

Do you actually mean convert an object in one language to an object in another? If so, what interface are you using (PyMat?) Or do you mean how do you print out a datetime object in a particular format? — David Robinson
– David Robinson, Commented Jan 8, 2012 at 9:20
@DavidRobinson - nope, I mean to datenum's textual representation which Matlab knows how to read. stuff like 732399.65465 where on the left is the gregorian day since 1/1/1 (or 1/1/0?!) and on the right is the fraction of a day — Jonathan Livni
– Jonathan Livni, Commented Jan 8, 2012 at 14:14

Roman Susi · Accepted Answer · 2012-01-08 09:31:39Z

9

To serialize datetime as a string, strftime can be used on the Python side:

import datetime
d = datetime.datetime.now()
print (d.strftime("%d-%b-%Y %H:%M:%S"))

According to MatLab docs datenum knows how to parse it.

answered Jan 8, 2012 at 9:31

Roman Susi

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Jonathan Livni · Accepted Answer · 2012-02-22 09:00:30Z

9

Based on bavaza's answer - now including microseconds:

def datetime2matlabdn(dt):
   mdn = dt + timedelta(days = 366)
   frac_seconds = (dt-datetime.datetime(dt.year,dt.month,dt.day,0,0,0)).seconds / (24.0 * 60.0 * 60.0)
   frac_microseconds = dt.microsecond / (24.0 * 60.0 * 60.0 * 1000000.0)
   return mdn.toordinal() + frac_seconds + frac_microseconds

answered Feb 22, 2012 at 9:00

Jonathan Livni

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Community · Accepted Answer · 2020-06-20 09:12:55Z

6

Reversing what was done here, I got:

def datetime2matlabdn(dt):
   ord = dt.toordinal()
   mdn = dt + timedelta(days = 366)
   frac = (dt-datetime(dt.year,dt.month,dt.day,0,0,0)).seconds / (24.0 * 60.0 * 60.0)
   return mdn.toordinal() + frac

Should work with timedelta.microseconds too.

In IDLE:

n = datetime.now()

datetime.datetime(2012, 2, 13, 6, 56, 2, 619000)

datetime2matlabdn(n)

734912.28891203704

In Matlab:

>> datestr(734912.28891203704)

ans = 13-Feb-2012 06:56:02

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Feb 13, 2012 at 11:57

bavaza

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2 Comments

Amro Over a year ago

+1 slightly off-topic, but I had to do a similar conversion between MATLAB datenum and C# System.DateTime in an old answer of mine. Beside the different units used internally, the reference point in time was also off by 366 days: stackoverflow.com/a/7558811/97160

Jonathan Livni Over a year ago

actually datestr(734912.28891203704, 'mmmm dd, yyyy HH:MM:SS.FFF AM') yields February 13, 2012 6:56:02.000 AM so it does not retain the milliseconds\microseconds information

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