Date Time and Datetime conversions

Date Time, Timestamp and Datetime conversions

Python has a great class for storing and manipulating the date and time: datetime.

Unfortunately, it is not the only way to refer to a point in time. Sometimes you need to convert between the two and I frequently forget how to do it.

Table of Conversions

Here is a table of conversions. Pick the row corresponding to the form of time that you have (from the left), and them pick the column corresponding to the form that you would like (from the top). The intersecting cell is the code snippet to get you there.

I have some measure of confidence in the correctness since the table, indeed, this entire post, was created by a script which tested the code shown in the table and lists below. That script is available here. However, I expect that many of the conversions can be improved upon and many may be subtly, or not so subtly, incorrect. Please let me know if you have an improvement.

• "dt" represents an input datetime.
• "t" represents an input time struct.
• "secs" represents an input timestamp (seconds since the Epoch GMT).
• "localtz" represents the local timezone. This is necessary to account for functions or formats that convert to or from the local timezone.
• "othertz" represents a timezone that you want to to have. It can be UTC or any other pytz timezone.
• You need to import "pytz" for timezones.
• You need to import the "datetime" class from the the datetime module.
• Note that time structs can not store time at a resolution finer than a second.

I'm sorry, but this table just isn't going to work on mobile. Below is a breakout by the type of representation that you are converting to.

Table of Conversions between various date and time formats

	To Timezone Naive Datetime Local	To Timezone Naive Datetime UTC	To Timezone Aware Datetime	To Time Struct Local	To Time Struct UTC	To Timestamp
Build as of now	datetime . now ( )	datetime . utcnow ( )	localtz . localize ( datetime . now ( ) ) . astimezone ( othertz )	time . localtime ( )	time . gmtime ( )	time . time ( )
From Timezone Naive Datetime Local		localtz . localize ( dt ) . astimezone ( pytz . utc ) . replace ( tzinfo = None )	localtz . localize ( dt ) . astimezone ( othertz )	dt . timetuple ( )	localtz . localize ( dt ) . utctimetuple ( )	time . mktime ( dt . timetuple ( ) ) + 1e-6 * dt . microsecond
From Timezone Naive Datetime UTC	pytz . utc . localize ( dt ) . astimezone ( localtz ) . replace ( tzinfo = None )		pytz . utc . localize ( dt ) . astimezone ( othertz )	pytz . utc . localize ( dt ) . astimezone ( localtz ) . timetuple ( )	dt . utctimetuple ( )	calendar . timegm ( pytz . utc . localize ( dt ) . timetuple ( ) ) + 1e-6 * dt . microsecond
From Timezone Aware Datetime	dt . astimezone ( localtz ) . replace ( tzinfo = None )	dt . astimezone ( pytz . utc ) . replace ( tzinfo = None )		dt . astimezone ( localtz ) . timetuple ( )	dt . utctimetuple ( )	calendar . timegm ( dt . utctimetuple ( ) ) + 1e-6 * dt . microsecond
From Time Struct Local	datetime ( *t[:6] )	datetime . utcfromtimestamp ( time . mktime ( t ) )	localtz . localize ( datetime ( *t[:6] ) ) . astimezone ( othertz )		time . gmtime ( time . mktime ( t ) )	time . mktime ( t )
From Time Struct UTC	pytz . utc . localize ( datetime ( *t[:6] ) ) . astimezone ( localtz ) . replace ( tzinfo = None )	datetime . utcfromtimestamp ( calendar . timegm ( t ) )	pytz . utc . localize ( datetime ( *t[:6] ) ) . astimezone ( othertz )	time . localtime ( calendar . timegm ( t ) )		calendar . timegm ( t )
From Timestamp	datetime . fromtimestamp ( secs )	datetime . utcfromtimestamp ( secs )	localtz . localize ( datetime . fromtimestamp ( secs ) )	time . localtime ( secs )	time . gmtime ( secs )

List of Specific Conversions

Timezone Naive Datetime Local

From	To Timezone Naive Datetime Local
Timezone Naive Datetime UTC	pytz.utc.localize(dt).astimezone(localtz).replace(tzinfo=None)
Timezone Aware Datetime	dt.astimezone(localtz).replace(tzinfo=None)
Time Struct Local	datetime(*t[:6])
Time Struct UTC	pytz.utc.localize(datetime(*t[:6])).astimezone(localtz).replace(tzinfo=None)
Timestamp	datetime.fromtimestamp(secs)

To build as of now: datetime.now()

Timezone Naive Datetime UTC

From	To Timezone Naive Datetime UTC
Timezone Naive Datetime Local	localtz.localize(dt).astimezone(pytz.utc).replace(tzinfo=None)
Timezone Aware Datetime	dt.astimezone(pytz.utc).replace(tzinfo=None)
Time Struct Local	datetime.utcfromtimestamp(time.mktime(t))
Time Struct UTC	datetime.utcfromtimestamp(calendar.timegm(t))
Timestamp	datetime.utcfromtimestamp(secs)

To build as of now: datetime.utcnow()

Timezone Aware Datetime

From	To Timezone Aware Datetime
Timezone Naive Datetime Local	localtz.localize(dt).astimezone(othertz)
Timezone Naive Datetime UTC	pytz.utc.localize(dt).astimezone(othertz)
Time Struct Local	localtz.localize(datetime(*t[:6])).astimezone(othertz)
Time Struct UTC	pytz.utc.localize(datetime(*t[:6])).astimezone(othertz)
Timestamp	localtz.localize(datetime.fromtimestamp(secs))

To build as of now: localtz.localize(datetime.now()).astimezone(othertz)

Time Struct Local

From	To Time Struct Local
Timezone Naive Datetime Local	dt.timetuple()
Timezone Naive Datetime UTC	pytz.utc.localize(dt).astimezone(localtz).timetuple()
Timezone Aware Datetime	dt.astimezone(localtz).timetuple()
Time Struct UTC	time.localtime(calendar.timegm(t))
Timestamp	time.localtime(secs)

To build as of now: time.localtime()

Time Struct UTC

From	To Time Struct UTC
Timezone Naive Datetime Local	localtz.localize(dt).utctimetuple()
Timezone Naive Datetime UTC	dt.utctimetuple()
Timezone Aware Datetime	dt.utctimetuple()
Time Struct Local	time.gmtime(time.mktime(t))
Timestamp	time.gmtime(secs)

To build as of now: time.gmtime()

Timestamp

From	To Timestamp
Timezone Naive Datetime Local	time.mktime(dt.timetuple())+1e-6*dt.microsecond
Timezone Naive Datetime UTC	calendar.timegm(pytz.utc.localize(dt).timetuple())+1e-6*dt.microsecond
Timezone Aware Datetime	calendar.timegm(dt.utctimetuple())+1e-6*dt.microsecond
Time Struct Local	time.mktime(t)
Time Struct UTC	calendar.timegm(t)

To build as of now: time.time()

Timezones

import pytz, datetime
pytz.timezone('UTC').localize(datetime.utcnow())
pytz.timezone('US/Central').localize(datetime.now())
print 'Common timezones:',pytz.common_timezones

References

• Even more formats.
• Time module.
• Datetime module.
• The pytz docs. say to never create a datetime with a timezone that has DST.