JSON datetime between Python and JavaScript

Question

I want to send a datetime datetime object in serialized form from Python using JSON and de-serialize in JavaScript using JSON  What is the best way to do this

User · Answer

Not much to add to the community wiki answer, except for timestamp!

Javascript uses the following format:

new Date().toJSON() // "2016-01-08T19:00:00.123Z"

Python side (for the json.dumps handler, see the other answers):

>>> from datetime import datetime
>>> d = datetime.strptime('2016-01-08T19:00:00.123Z', '%Y-%m-%dT%H:%M:%S.%fZ')
>>> d
datetime.datetime(2016, 1, 8, 19, 0, 0, 123000)
>>> d.isoformat() + 'Z'
'2016-01-08T19:00:00.123000Z'

If you leave that Z out, frontend frameworks like angular can not display the date in browser-local timezone:

> $filter('date')('2016-01-08T19:00:00.123000Z', 'yyyy-MM-dd HH:mm:ss')
"2016-01-08 20:00:00"
> $filter('date')('2016-01-08T19:00:00.123000', 'yyyy-MM-dd HH:mm:ss')
"2016-01-08 19:00:00"

User · Answer

If you re certain that only Javascript will be consuming the JSON  I prefer to pass Javascript Date objects directly   The ctime   method on datetime objects will return a string that the Javascript Date object can understand   import datetime date   datetime datetime today   json      mydate  new Date   s       date ctime     Javascript will happily use that as an object literal  and you ve got your Date object built right in

User · Answer

For cross-language projects  I found out that strings containing RfC 3339 dates are the best way to go  An RfC 3339 date looks like this     1985-04-12T23 20 50 52Z   I think most of the format is obvious  The only somewhat unusual thing may be the  Z  at the end  It stands for GMT UTC  You could also add a timezone offset like  02 00 for CEST  Germany in summer   I personally prefer to keep everything in UTC until it is displayed   For displaying  comparisons and storage you can leave it in string format across all languages  If you need the date for calculations easy to convert it back to a native date object in most language   So generate the JSON like this     json dump datetime now   strftime   Y- m- dT H  M  SZ      Unfortunately  Javascript s Date constructor doesn t accept RfC 3339 strings but there are many parsers available on the Internet   huTools hujson tries to handle the most common encoding issues you might come across in Python code including date datetime objects while handling timezones correctly

User · Answer

Here s a fairly complete solution for recursively encoding and decoding datetime datetime and datetime date objects using the standard library json module  This needs Python    2 6 since the  f format code in the datetime datetime strptime   format string is only supported in since then  For Python 2 5 support  drop the  f and strip the microseconds from the ISO date string before trying to convert it  but you ll loose microseconds precision  of course  For interoperability with ISO date strings from other sources  which may include a time zone name or UTC offset  you may also need to strip some parts of the date string before the conversion  For a complete parser for ISO date strings  and many other date formats  see the third-party dateutil module   Decoding only works when the ISO date strings are values in a JavaScript literal object notation or in nested structures within an object  ISO date strings  which are items of a top-level array will not be decoded   I e  this works   date   datetime datetime now    gt  gt  gt  json   dumps dict foo  bar   innerdict dict date date     gt  gt  gt  json    innerdict     date    2010-07-15T13 16 38 365579     foo    bar     gt  gt  gt  loads json   u innerdict    u date   datetime datetime 2010  7  15  13  16  38  365579    u foo   u bar     And this too    gt  gt  gt  json   dumps   foo    bar   dict date date     gt  gt  gt  json    foo    bar     date    2010-07-15T13 16 38 365579      gt  gt  gt  loads json   u foo   u bar    u date   datetime datetime 2010  7  15  13  16  38  365579      But this doesn t work as expected    gt  gt  gt  json   dumps   foo    bar   date    gt  gt  gt  json    foo    bar    2010-07-15T13 16 38 365579     gt  gt  gt  loads json   u foo   u bar   u 2010-07-15T13 16 38 365579     Here s the code     all       dumps    loads    import datetime  try      import json except ImportError      import simplejson as json  class JSONDateTimeEncoder json JSONEncoder       def default self  obj           if isinstance obj   datetime date  datetime datetime                return obj isoformat           else              return json JSONEncoder default self  obj   def datetime decoder d       if isinstance d  list           pairs   enumerate d      elif isinstance d  dict           pairs   d items       result          for k v in pairs          if isinstance v  basestring               try                    The  f format code is only supported in Python  gt   2 6                    For Python  lt   2 5 strip off microseconds                   v   datetime datetime strptime v rsplit      1  0                           Y- m- dT H  M  S                   v   datetime datetime strptime v    Y- m- dT H  M  S  f               except ValueError                  try                      v   datetime datetime strptime v    Y- m- d   date                   except ValueError                      pass         elif isinstance v   dict  list                v   datetime decoder v          result append  k  v       if isinstance d  list           return  x 1  for x in result      elif isinstance d  dict           return dict result   def dumps obj       return json dumps obj  cls JSONDateTimeEncoder   def loads obj       return json loads obj  object hook datetime decoder   if   name         main         mytimestamp   datetime datetime utcnow       mydate   datetime date today       data   dict          foo   42          bar    mytimestamp  mydate           date   mydate          timestamp   mytimestamp          struct   dict              date2   mydate              timestamp2   mytimestamp                      print repr data      jsonstring   dumps data      print jsonstring     print repr loads jsonstring

User · Answer

My advice is to use a library  There are several available at pypi org   I use this one  it it works good  https   pypi python org pypi asjson

User · Answer

Apparently The    right    JSON  well JavaScript  date format is 2012-04-23T18 25 43 511Z - UTC and  Z    Without this JavaScript will use the web browser s local timezone when creating a Date   object from the string   For a  naive  time  what Python calls a time with no timezone and this assumes is local  the below will force local timezone so that it can then be correctly converted to UTC   def default obj       if hasattr obj   json   and callable getattr obj   json             return obj json       if hasattr obj   isoformat   and callable getattr obj   isoformat               date time objects         if not obj utcoffset                  add local timezone to  naive  local time               https   stackoverflow com questions 2720319 python-figure-out-local-timezone             tzinfo   datetime now timezone utc  astimezone   tzinfo             obj   obj replace tzinfo tzinfo            convert to UTC         obj   obj astimezone timezone utc            strip the UTC offset         obj   obj replace tzinfo None          return obj isoformat      Z      elif hasattr obj     str     and callable getattr obj     str               return str obj      else          print  obj    obj          raise TypeError obj   def dump j  io       json dump j  io  indent 2  default default    why is this so hard

User · Answer

For the Python to JavaScript date conversion  the date object needs to be in specific ISO format  i e  ISO format or UNIX number  If the ISO format lacks some info  then you can convert to the Unix number with Date parse first  Moreover  Date parse works with React as well while new Date might trigger an exception    In case you have a DateTime object without milliseconds  the following needs to be considered       var unixDate   Date parse  2016-01-08T19 00 00      var desiredDate   new Date unixDate  toLocaleDateString      The example date could equally be a variable in the result data object after an API call   For options to display the date in the desired format  e g  to display long weekdays  check out the MDN doc

User · Answer

Late in the game         A very simple solution is to patch the json module default   For example   import json import datetime  json JSONEncoder default   lambda self obj   obj isoformat   if isinstance obj  datetime datetime  else None    Now  you can use json dumps   as if it had always supported datetime     json dumps   created  datetime datetime now       This makes sense if you require this extension to the json module to always kick in and wish to not change the way you or others use json serialization  either in existing code or not     Note that some may consider patching libraries in that way as bad practice  Special care need to be taken in case you may wish to extend your application in more than one way - is such a case  I suggest to use the solution by ramen or JT and choose the proper json extension in each case

User · Answer

For cross-language projects  I found out that strings containing RfC 3339 dates are the best way to go  An RfC 3339 date looks like this     1985-04-12T23 20 50 52Z   I think most of the format is obvious  The only somewhat unusual thing may be the  Z  at the end  It stands for GMT UTC  You could also add a timezone offset like  02 00 for CEST  Germany in summer   I personally prefer to keep everything in UTC until it is displayed   For displaying  comparisons and storage you can leave it in string format across all languages  If you need the date for calculations easy to convert it back to a native date object in most language   So generate the JSON like this     json dump datetime now   strftime   Y- m- dT H  M  SZ      Unfortunately  Javascript s Date constructor doesn t accept RfC 3339 strings but there are many parsers available on the Internet   huTools hujson tries to handle the most common encoding issues you might come across in Python code including date datetime objects while handling timezones correctly

User · Answer

For the Python to JavaScript date conversion  the date object needs to be in specific ISO format  i e  ISO format or UNIX number  If the ISO format lacks some info  then you can convert to the Unix number with Date parse first  Moreover  Date parse works with React as well while new Date might trigger an exception    In case you have a DateTime object without milliseconds  the following needs to be considered       var unixDate   Date parse  2016-01-08T19 00 00      var desiredDate   new Date unixDate  toLocaleDateString      The example date could equally be a variable in the result data object after an API call   For options to display the date in the desired format  e g  to display long weekdays  check out the MDN doc

User · Answer

You can add the  default  parameter to json dumps to handle this   date handler   lambda obj        obj isoformat       if isinstance obj   datetime datetime  datetime date       else None   json dumps datetime datetime now    default date handler    2010-04-20T20 08 21 634121     Which is ISO 8601 format    A more comprehensive default handler function   def handler obj       if hasattr obj   isoformat            return obj isoformat       elif isinstance obj                return         else          raise TypeError   Object of type  s with value of  s is not JSON serializable     type obj   repr obj     Update   Added output of type as well as value  Update   Also handle date

User · Answer

If you re certain that only Javascript will be consuming the JSON  I prefer to pass Javascript Date objects directly   The ctime   method on datetime objects will return a string that the Javascript Date object can understand   import datetime date   datetime datetime today   json      mydate  new Date   s       date ctime     Javascript will happily use that as an object literal  and you ve got your Date object built right in

User · Answer

Here s a fairly complete solution for recursively encoding and decoding datetime datetime and datetime date objects using the standard library json module  This needs Python    2 6 since the  f format code in the datetime datetime strptime   format string is only supported in since then  For Python 2 5 support  drop the  f and strip the microseconds from the ISO date string before trying to convert it  but you ll loose microseconds precision  of course  For interoperability with ISO date strings from other sources  which may include a time zone name or UTC offset  you may also need to strip some parts of the date string before the conversion  For a complete parser for ISO date strings  and many other date formats  see the third-party dateutil module   Decoding only works when the ISO date strings are values in a JavaScript literal object notation or in nested structures within an object  ISO date strings  which are items of a top-level array will not be decoded   I e  this works   date   datetime datetime now    gt  gt  gt  json   dumps dict foo  bar   innerdict dict date date     gt  gt  gt  json    innerdict     date    2010-07-15T13 16 38 365579     foo    bar     gt  gt  gt  loads json   u innerdict    u date   datetime datetime 2010  7  15  13  16  38  365579    u foo   u bar     And this too    gt  gt  gt  json   dumps   foo    bar   dict date date     gt  gt  gt  json    foo    bar     date    2010-07-15T13 16 38 365579      gt  gt  gt  loads json   u foo   u bar    u date   datetime datetime 2010  7  15  13  16  38  365579      But this doesn t work as expected    gt  gt  gt  json   dumps   foo    bar   date    gt  gt  gt  json    foo    bar    2010-07-15T13 16 38 365579     gt  gt  gt  loads json   u foo   u bar   u 2010-07-15T13 16 38 365579     Here s the code     all       dumps    loads    import datetime  try      import json except ImportError      import simplejson as json  class JSONDateTimeEncoder json JSONEncoder       def default self  obj           if isinstance obj   datetime date  datetime datetime                return obj isoformat           else              return json JSONEncoder default self  obj   def datetime decoder d       if isinstance d  list           pairs   enumerate d      elif isinstance d  dict           pairs   d items       result          for k v in pairs          if isinstance v  basestring               try                    The  f format code is only supported in Python  gt   2 6                    For Python  lt   2 5 strip off microseconds                   v   datetime datetime strptime v rsplit      1  0                           Y- m- dT H  M  S                   v   datetime datetime strptime v    Y- m- dT H  M  S  f               except ValueError                  try                      v   datetime datetime strptime v    Y- m- d   date                   except ValueError                      pass         elif isinstance v   dict  list                v   datetime decoder v          result append  k  v       if isinstance d  list           return  x 1  for x in result      elif isinstance d  dict           return dict result   def dumps obj       return json dumps obj  cls JSONDateTimeEncoder   def loads obj       return json loads obj  object hook datetime decoder   if   name         main         mytimestamp   datetime datetime utcnow       mydate   datetime date today       data   dict          foo   42          bar    mytimestamp  mydate           date   mydate          timestamp   mytimestamp          struct   dict              date2   mydate              timestamp2   mytimestamp                      print repr data      jsonstring   dumps data      print jsonstring     print repr loads jsonstring

User · Answer

For cross-language projects  I found out that strings containing RfC 3339 dates are the best way to go  An RfC 3339 date looks like this     1985-04-12T23 20 50 52Z   I think most of the format is obvious  The only somewhat unusual thing may be the  Z  at the end  It stands for GMT UTC  You could also add a timezone offset like  02 00 for CEST  Germany in summer   I personally prefer to keep everything in UTC until it is displayed   For displaying  comparisons and storage you can leave it in string format across all languages  If you need the date for calculations easy to convert it back to a native date object in most language   So generate the JSON like this     json dump datetime now   strftime   Y- m- dT H  M  SZ      Unfortunately  Javascript s Date constructor doesn t accept RfC 3339 strings but there are many parsers available on the Internet   huTools hujson tries to handle the most common encoding issues you might come across in Python code including date datetime objects while handling timezones correctly

User · Answer

I ve worked it out   Let s say you have a Python datetime object  d  created with datetime now    Its value is   datetime datetime 2011  5  25  13  34  5  787000    You can serialize it to JSON as an ISO 8601 datetime string   import json     json dumps d isoformat      The example datetime object would be serialized as     2011-05-25T13 34 05 787000     This value  once received in the Javascript layer  can construct a Date object   var d   new Date  2011-05-25T13 34 05 787000      As of Javascript 1 8 5  Date objects have a toJSON method  which returns a string in a standard format  To serialize the above Javascript object back to JSON  therefore  the command would be   d toJSON     Which would give you    2011-05-25T20 34 05 787Z    This string  once received in Python  could be deserialized back to a datetime object   datetime strptime  2011-05-25T20 34 05 787Z     Y- m- dT H  M  S  fZ     This results in the following datetime object  which is the same one you started with and therefore correct   datetime datetime 2011  5  25  20  34  5  787000

User · Answer

My advice is to use a library  There are several available at pypi org   I use this one  it it works good  https   pypi python org pypi asjson

User · Answer

Using json  you can subclass JSONEncoder and override the default   method to provide your own custom serializers   import json import datetime  class DateTimeJSONEncoder json JSONEncoder       def default self  obj           if isinstance obj  datetime datetime               return obj isoformat           else              return super DateTimeJSONEncoder  self  default obj    Then  you can call it like this    gt  gt  gt  DateTimeJSONEncoder   encode  datetime datetime now        2010-06-15T14 42 28

User · Answer

If you re certain that only Javascript will be consuming the JSON  I prefer to pass Javascript Date objects directly   The ctime   method on datetime objects will return a string that the Javascript Date object can understand   import datetime date   datetime datetime today   json      mydate  new Date   s       date ctime     Javascript will happily use that as an object literal  and you ve got your Date object built right in

User · Answer

Late in the game         A very simple solution is to patch the json module default   For example   import json import datetime  json JSONEncoder default   lambda self obj   obj isoformat   if isinstance obj  datetime datetime  else None    Now  you can use json dumps   as if it had always supported datetime     json dumps   created  datetime datetime now       This makes sense if you require this extension to the json module to always kick in and wish to not change the way you or others use json serialization  either in existing code or not     Note that some may consider patching libraries in that way as bad practice  Special care need to be taken in case you may wish to extend your application in more than one way - is such a case  I suggest to use the solution by ramen or JT and choose the proper json extension in each case

User · Answer

Using json  you can subclass JSONEncoder and override the default   method to provide your own custom serializers   import json import datetime  class DateTimeJSONEncoder json JSONEncoder       def default self  obj           if isinstance obj  datetime datetime               return obj isoformat           else              return super DateTimeJSONEncoder  self  default obj    Then  you can call it like this    gt  gt  gt  DateTimeJSONEncoder   encode  datetime datetime now        2010-06-15T14 42 28

User · Answer

If you re certain that only Javascript will be consuming the JSON  I prefer to pass Javascript Date objects directly   The ctime   method on datetime objects will return a string that the Javascript Date object can understand   import datetime date   datetime datetime today   json      mydate  new Date   s       date ctime     Javascript will happily use that as an object literal  and you ve got your Date object built right in

User · Answer

Not much to add to the community wiki answer, except for timestamp!

Javascript uses the following format:

new Date().toJSON() // "2016-01-08T19:00:00.123Z"

Python side (for the json.dumps handler, see the other answers):

>>> from datetime import datetime
>>> d = datetime.strptime('2016-01-08T19:00:00.123Z', '%Y-%m-%dT%H:%M:%S.%fZ')
>>> d
datetime.datetime(2016, 1, 8, 19, 0, 0, 123000)
>>> d.isoformat() + 'Z'
'2016-01-08T19:00:00.123000Z'

If you leave that Z out, frontend frameworks like angular can not display the date in browser-local timezone:

> $filter('date')('2016-01-08T19:00:00.123000Z', 'yyyy-MM-dd HH:mm:ss')
"2016-01-08 20:00:00"
> $filter('date')('2016-01-08T19:00:00.123000', 'yyyy-MM-dd HH:mm:ss')
"2016-01-08 19:00:00"

User · Answer

I ve worked it out   Let s say you have a Python datetime object  d  created with datetime now    Its value is   datetime datetime 2011  5  25  13  34  5  787000    You can serialize it to JSON as an ISO 8601 datetime string   import json     json dumps d isoformat      The example datetime object would be serialized as     2011-05-25T13 34 05 787000     This value  once received in the Javascript layer  can construct a Date object   var d   new Date  2011-05-25T13 34 05 787000      As of Javascript 1 8 5  Date objects have a toJSON method  which returns a string in a standard format  To serialize the above Javascript object back to JSON  therefore  the command would be   d toJSON     Which would give you    2011-05-25T20 34 05 787Z    This string  once received in Python  could be deserialized back to a datetime object   datetime strptime  2011-05-25T20 34 05 787Z     Y- m- dT H  M  S  fZ     This results in the following datetime object  which is the same one you started with and therefore correct   datetime datetime 2011  5  25  20  34  5  787000

User · Answer

On python side   import time  json from datetime import datetime as dt your date   dt now   data   json dumps time mktime your date timetuple    1000  return data   data send to javascript   On javascript side   var your date   new Date data    where data is result from python

User · Answer

You can add the  default  parameter to json dumps to handle this   date handler   lambda obj        obj isoformat       if isinstance obj   datetime datetime  datetime date       else None   json dumps datetime datetime now    default date handler    2010-04-20T20 08 21 634121     Which is ISO 8601 format    A more comprehensive default handler function   def handler obj       if hasattr obj   isoformat            return obj isoformat       elif isinstance obj                return         else          raise TypeError   Object of type  s with value of  s is not JSON serializable     type obj   repr obj     Update   Added output of type as well as value  Update   Also handle date

User · Answer

For cross-language projects  I found out that strings containing RfC 3339 dates are the best way to go  An RfC 3339 date looks like this     1985-04-12T23 20 50 52Z   I think most of the format is obvious  The only somewhat unusual thing may be the  Z  at the end  It stands for GMT UTC  You could also add a timezone offset like  02 00 for CEST  Germany in summer   I personally prefer to keep everything in UTC until it is displayed   For displaying  comparisons and storage you can leave it in string format across all languages  If you need the date for calculations easy to convert it back to a native date object in most language   So generate the JSON like this     json dump datetime now   strftime   Y- m- dT H  M  SZ      Unfortunately  Javascript s Date constructor doesn t accept RfC 3339 strings but there are many parsers available on the Internet   huTools hujson tries to handle the most common encoding issues you might come across in Python code including date datetime objects while handling timezones correctly

User · Answer

Apparently The    right    JSON  well JavaScript  date format is 2012-04-23T18 25 43 511Z - UTC and  Z    Without this JavaScript will use the web browser s local timezone when creating a Date   object from the string   For a  naive  time  what Python calls a time with no timezone and this assumes is local  the below will force local timezone so that it can then be correctly converted to UTC   def default obj       if hasattr obj   json   and callable getattr obj   json             return obj json       if hasattr obj   isoformat   and callable getattr obj   isoformat               date time objects         if not obj utcoffset                  add local timezone to  naive  local time               https   stackoverflow com questions 2720319 python-figure-out-local-timezone             tzinfo   datetime now timezone utc  astimezone   tzinfo             obj   obj replace tzinfo tzinfo            convert to UTC         obj   obj astimezone timezone utc            strip the UTC offset         obj   obj replace tzinfo None          return obj isoformat      Z      elif hasattr obj     str     and callable getattr obj     str               return str obj      else          print  obj    obj          raise TypeError obj   def dump j  io       json dump j  io  indent 2  default default    why is this so hard

User · Answer

On python side   import time  json from datetime import datetime as dt your date   dt now   data   json dumps time mktime your date timetuple    1000  return data   data send to javascript   On javascript side   var your date   new Date data    where data is result from python

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