How do I get a Cron like scheduler in Python

Question

I m looking for a library in Python which will provide at and cron like functionality   I d quite like have a pure Python solution  rather than relying on tools installed on the box  this way I run on machines with no cron   For those unfamiliar with cron  you can schedule tasks based upon an expression like     0 2     7  usr bin run-backup   run the backups at 0200 on Every Sunday  0 9-17 2     1-5  usr bin purge-temps   run the purge temps command  every 2 hours between 9am and 5pm on Mondays to Fridays    The cron time expression syntax is less important  but I would like to have something with this sort of flexibility    If there isn t something that does this for me out-the-box  any suggestions for the building blocks to make something like this would be gratefully received   Edit I m not interested in launching processes  just  jobs  also written in Python - python functions  By necessity I think this would be a different thread  but not in a different process   To this end  I m looking for the expressivity of the cron time expression  but in Python    Cron has been around for years  but I m trying to be as portable as possible  I cannot rely on its presence

User · Answer

Another trivial solution would be   from aqcron import At from time import sleep from datetime import datetime    Event scheduling event 1   At  second 5   event 2   At  second  0 20 40     while True      now   datetime now          Event check     if now in event 1  print  event 1      if now in event 2  print  event 2       sleep 1    And the class aqcron At is     aqcron py  class At object       def   init   self  year None     month None                   day None      weekday None                   hour None     minute None                   second None           loc   locals           loc pop  self           self at   dict  k  v  for k  v in loc iteritems   if v    None       def   contains   self  now           for k in self at keys                try                  if not getattr now  k  in self at k   return False             except TypeError                  if self at k     getattr now  k   return False         return True

User · Answer

There isn t a  pure python  way to do this because some other process would have to launch python in order to run your solution   Every platform will have one or twenty different ways to launch processes and monitor their progress   On unix platforms  cron is the old standard   On Mac OS X there is also launchd  which combines cron-like launching with watchdog functionality that can keep your process alive if that s what you want  Once python is running  then you can use the sched module to schedule tasks

User · Answer

Another trivial solution would be   from aqcron import At from time import sleep from datetime import datetime    Event scheduling event 1   At  second 5   event 2   At  second  0 20 40     while True      now   datetime now          Event check     if now in event 1  print  event 1      if now in event 2  print  event 2       sleep 1    And the class aqcron At is     aqcron py  class At object       def   init   self  year None     month None                   day None      weekday None                   hour None     minute None                   second None           loc   locals           loc pop  self           self at   dict  k  v  for k  v in loc iteritems   if v    None       def   contains   self  now           for k in self at keys                try                  if not getattr now  k  in self at k   return False             except TypeError                  if self at k     getattr now  k   return False         return True

User · Answer

I like how the pycron package solves this problem  import pycron import time  while True      if pycron is now  0 2     0        True Every Sunday at 02 00         print  running backup           time sleep 60                  The process should take at least 60 sec                                        to avoid running twice in one minute     else          time sleep 15                  Check again in 15 seconds

User · Answer

I know there are a lot of answers  but another solution could be to go with decorators  This is an example to repeat a function everyday at a specific time  The cool think about using this way is that you only need to add the Syntactic Sugar to the function you want to schedule     repeatEveryDay hour 6  minutes 30  def sayHello name       print f Hello  name     sayHello  Bob     Now this function will be invoked every day at 6 30 a m   And the decorator will look like   def repeatEveryDay hour  minutes 0  seconds 0               Decorator that will run the decorated function everyday at that hour  minutes and seconds       param hour  0-24      param minutes  0-60  Optional       param seconds  0-60  Optional              def decoratorRepeat func             functools wraps func          def wrapperRepeat  args    kwargs                def getLocalTime                    return datetime datetime fromtimestamp time mktime time localtime                     Get the datetime of the first function call             td   datetime timedelta seconds 15              if wrapperRepeat nextSent    None                  now   getLocalTime                   wrapperRepeat nextSent   datetime datetime now year  now month  now day  hour  minutes  seconds                  if wrapperRepeat nextSent  lt  now                      wrapperRepeat nextSent    td                Waiting till next day             while getLocalTime    lt  wrapperRepeat nextSent                  time sleep 1                 Call the function             func  args    kwargs                  Get the datetime of the next function call             wrapperRepeat nextSent    td             wrapperRepeat  args    kwargs           wrapperRepeat nextSent   None         return wrapperRepeat      return decoratorRepeat

User · Answer

There isn t a  pure python  way to do this because some other process would have to launch python in order to run your solution   Every platform will have one or twenty different ways to launch processes and monitor their progress   On unix platforms  cron is the old standard   On Mac OS X there is also launchd  which combines cron-like launching with watchdog functionality that can keep your process alive if that s what you want  Once python is running  then you can use the sched module to schedule tasks

User · Answer

I don t know if something like that already exists  It would be easy to write your own with time  datetime and or calendar modules  see http   docs python org library time html  The only concern for a python solution is that your job needs to be always running and possibly be automatically  resurrected  after a reboot  something for which you do need to rely on system dependent solutions

User · Answer

There isn t a  pure python  way to do this because some other process would have to launch python in order to run your solution   Every platform will have one or twenty different ways to launch processes and monitor their progress   On unix platforms  cron is the old standard   On Mac OS X there is also launchd  which combines cron-like launching with watchdog functionality that can keep your process alive if that s what you want  Once python is running  then you can use the sched module to schedule tasks

User · Answer

You could just use normal Python argument passing syntax to specify your crontab   For example  suppose we define an Event class as below   from datetime import datetime  timedelta import time    Some utility classes   functions first class AllMatch set          Universal set - match everything        def   contains   self  item   return True  allMatch   AllMatch    def conv to set obj      Allow single integer to be provided     if isinstance obj   int long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj    The actual Event class class Event object       def   init   self  action  min allMatch  hour allMatch                          day allMatch  month allMatch  dow allMatch                          args     kwargs              self mins   conv to set min          self hours  conv to set hour          self days   conv to set day          self months   conv to set month          self dow   conv to set dow          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t              Return True if this event should trigger at the specified datetime            return   t minute     in self mins  and                  t hour       in self hours  and                  t day        in self days  and                  t month      in self months  and                  t weekday    in self dow        def check self  t           if self matchtime t               self action  self args    self kwargs     Note  Not thoroughly tested   Then your CronTab can be specified in normal python syntax as   c   CronTab    Event perform backup  0  2  dow 6      Event purge temps  0  range 9 18 2   dow range 0 5       This way you get the full power of Python s argument mechanics  mixing positional and keyword args  and can use symbolic names for names of weeks and months   The CronTab class would be defined as simply sleeping in minute increments  and calling check   on each event    There are probably some subtleties with daylight savings time   timezones to be wary of though    Here s a quick implementation   class CronTab object       def   init   self   events           self events   events      def run self           t datetime  datetime now   timetuple    5           while 1              for e in self events                  e check t               t    timedelta minutes 1              while datetime now    lt  t                  time sleep  t - datetime now    seconds    A few things to note   Python s weekdays   months are zero indexed  unlike cron   and that range excludes the last element  hence syntax like  1-5  becomes range 0 5  - ie  0 1 2 3 4    If you prefer cron syntax  parsing it shouldn t be too difficult however

User · Answer

I know there are a lot of answers  but another solution could be to go with decorators  This is an example to repeat a function everyday at a specific time  The cool think about using this way is that you only need to add the Syntactic Sugar to the function you want to schedule     repeatEveryDay hour 6  minutes 30  def sayHello name       print f Hello  name     sayHello  Bob     Now this function will be invoked every day at 6 30 a m   And the decorator will look like   def repeatEveryDay hour  minutes 0  seconds 0               Decorator that will run the decorated function everyday at that hour  minutes and seconds       param hour  0-24      param minutes  0-60  Optional       param seconds  0-60  Optional              def decoratorRepeat func             functools wraps func          def wrapperRepeat  args    kwargs                def getLocalTime                    return datetime datetime fromtimestamp time mktime time localtime                     Get the datetime of the first function call             td   datetime timedelta seconds 15              if wrapperRepeat nextSent    None                  now   getLocalTime                   wrapperRepeat nextSent   datetime datetime now year  now month  now day  hour  minutes  seconds                  if wrapperRepeat nextSent  lt  now                      wrapperRepeat nextSent    td                Waiting till next day             while getLocalTime    lt  wrapperRepeat nextSent                  time sleep 1                 Call the function             func  args    kwargs                  Get the datetime of the next function call             wrapperRepeat nextSent    td             wrapperRepeat  args    kwargs           wrapperRepeat nextSent   None         return wrapperRepeat      return decoratorRepeat

User · Answer

None of the listed solutions even attempt to parse a complex cron schedule string  So  here is my version  using croniter  Basic gist   schedule      5            Run every five minutes  nextRunTime   getNextCronRunTime schedule  while True       roundedDownTime   roundDownTime        if  roundedDownTime    nextRunTime                                                              Do your periodic thing here                                                             nextRunTime   getNextCronRunTime schedule       elif  roundedDownTime  gt  nextRunTime              We missed an execution  Error  Re initialize           nextRunTime   getNextCronRunTime schedule       sleepTillTopOfNextMinute     Helper routines   from croniter import croniter from datetime import datetime  timedelta    Round time down to the top of the previous minute def roundDownTime dt None  dateDelta timedelta minutes 1        roundTo   dateDelta total seconds       if dt    None   dt   datetime now       seconds    dt - dt min  seconds     rounding    seconds roundTo 2     roundTo   roundTo     return dt   timedelta 0 rounding-seconds -dt microsecond     Get next run time from now  based on schedule specified by cron string def getNextCronRunTime schedule       return croniter schedule  datetime now    get next datetime     Sleep till the top of the next minute def sleepTillTopOfNextMinute        t   datetime utcnow       sleeptime   60 -  t second   t microsecond 1000000 0      time sleep sleeptime

User · Answer

I don t know if something like that already exists  It would be easy to write your own with time  datetime and or calendar modules  see http   docs python org library time html  The only concern for a python solution is that your job needs to be always running and possibly be automatically  resurrected  after a reboot  something for which you do need to rely on system dependent solutions

User · Answer

I don t know if something like that already exists  It would be easy to write your own with time  datetime and or calendar modules  see http   docs python org library time html  The only concern for a python solution is that your job needs to be always running and possibly be automatically  resurrected  after a reboot  something for which you do need to rely on system dependent solutions

User · Answer

You could just use normal Python argument passing syntax to specify your crontab   For example  suppose we define an Event class as below   from datetime import datetime  timedelta import time    Some utility classes   functions first class AllMatch set          Universal set - match everything        def   contains   self  item   return True  allMatch   AllMatch    def conv to set obj      Allow single integer to be provided     if isinstance obj   int long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj    The actual Event class class Event object       def   init   self  action  min allMatch  hour allMatch                          day allMatch  month allMatch  dow allMatch                          args     kwargs              self mins   conv to set min          self hours  conv to set hour          self days   conv to set day          self months   conv to set month          self dow   conv to set dow          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t              Return True if this event should trigger at the specified datetime            return   t minute     in self mins  and                  t hour       in self hours  and                  t day        in self days  and                  t month      in self months  and                  t weekday    in self dow        def check self  t           if self matchtime t               self action  self args    self kwargs     Note  Not thoroughly tested   Then your CronTab can be specified in normal python syntax as   c   CronTab    Event perform backup  0  2  dow 6      Event purge temps  0  range 9 18 2   dow range 0 5       This way you get the full power of Python s argument mechanics  mixing positional and keyword args  and can use symbolic names for names of weeks and months   The CronTab class would be defined as simply sleeping in minute increments  and calling check   on each event    There are probably some subtleties with daylight savings time   timezones to be wary of though    Here s a quick implementation   class CronTab object       def   init   self   events           self events   events      def run self           t datetime  datetime now   timetuple    5           while 1              for e in self events                  e check t               t    timedelta minutes 1              while datetime now    lt  t                  time sleep  t - datetime now    seconds    A few things to note   Python s weekdays   months are zero indexed  unlike cron   and that range excludes the last element  hence syntax like  1-5  becomes range 0 5  - ie  0 1 2 3 4    If you prefer cron syntax  parsing it shouldn t be too difficult however

User · Answer

There isn t a  pure python  way to do this because some other process would have to launch python in order to run your solution   Every platform will have one or twenty different ways to launch processes and monitor their progress   On unix platforms  cron is the old standard   On Mac OS X there is also launchd  which combines cron-like launching with watchdog functionality that can keep your process alive if that s what you want  Once python is running  then you can use the sched module to schedule tasks

User · Answer

You could just use normal Python argument passing syntax to specify your crontab   For example  suppose we define an Event class as below   from datetime import datetime  timedelta import time    Some utility classes   functions first class AllMatch set          Universal set - match everything        def   contains   self  item   return True  allMatch   AllMatch    def conv to set obj      Allow single integer to be provided     if isinstance obj   int long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj    The actual Event class class Event object       def   init   self  action  min allMatch  hour allMatch                          day allMatch  month allMatch  dow allMatch                          args     kwargs              self mins   conv to set min          self hours  conv to set hour          self days   conv to set day          self months   conv to set month          self dow   conv to set dow          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t              Return True if this event should trigger at the specified datetime            return   t minute     in self mins  and                  t hour       in self hours  and                  t day        in self days  and                  t month      in self months  and                  t weekday    in self dow        def check self  t           if self matchtime t               self action  self args    self kwargs     Note  Not thoroughly tested   Then your CronTab can be specified in normal python syntax as   c   CronTab    Event perform backup  0  2  dow 6      Event purge temps  0  range 9 18 2   dow range 0 5       This way you get the full power of Python s argument mechanics  mixing positional and keyword args  and can use symbolic names for names of weeks and months   The CronTab class would be defined as simply sleeping in minute increments  and calling check   on each event    There are probably some subtleties with daylight savings time   timezones to be wary of though    Here s a quick implementation   class CronTab object       def   init   self   events           self events   events      def run self           t datetime  datetime now   timetuple    5           while 1              for e in self events                  e check t               t    timedelta minutes 1              while datetime now    lt  t                  time sleep  t - datetime now    seconds    A few things to note   Python s weekdays   months are zero indexed  unlike cron   and that range excludes the last element  hence syntax like  1-5  becomes range 0 5  - ie  0 1 2 3 4    If you prefer cron syntax  parsing it shouldn t be too difficult however

User · Answer

More or less same as above but concurrent using gevent        Gevent based crontab implementation     from datetime import datetime  timedelta import gevent    Some utility classes   functions first def conv to set obj          Converts to set allowing single integer to be provided         if isinstance obj   int  long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj  class AllMatch set          Universal set - match everything        def   contains   self  item            return True  allMatch   AllMatch    class Event object          The Actual Event Class         def   init   self  action  minute allMatch  hour allMatch                          day allMatch  month allMatch  daysofweek allMatch                          args     kwargs              self mins   conv to set minute          self hours   conv to set hour          self days   conv to set day          self months   conv to set month          self daysofweek   conv to set daysofweek          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t1              Return True if this event should trigger at the specified datetime            return   t1 minute     in self mins  and                  t1 hour       in self hours  and                  t1 day        in self days  and                  t1 month      in self months  and                  t1 weekday    in self daysofweek        def check self  t              Check and run action if needed             if self matchtime t               self action  self args    self kwargs   class CronTab object          The crontab implementation         def   init   self   events           self events   events      def  check self              Check all events in separate greenlets             t1   datetime  datetime now   timetuple    5           for event in self events              gevent spawn event check  t1           t1    timedelta minutes 1          s1    t1 - datetime now    seconds   1         print  Checking again in  s seconds    s1         job   gevent spawn later s1  self  check       def run self              Run the cron forever             self  check           while True              gevent sleep 60   import os  def test task           Just an example that sends a bell and asd to all terminals         os system  echo asd   wall      cron   CronTab    Event test task  22  1      Event test task  0  range 9 18 2   daysofweek range 0 5      cron run

User · Answer

More or less same as above but concurrent using gevent        Gevent based crontab implementation     from datetime import datetime  timedelta import gevent    Some utility classes   functions first def conv to set obj          Converts to set allowing single integer to be provided         if isinstance obj   int  long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj  class AllMatch set          Universal set - match everything        def   contains   self  item            return True  allMatch   AllMatch    class Event object          The Actual Event Class         def   init   self  action  minute allMatch  hour allMatch                          day allMatch  month allMatch  daysofweek allMatch                          args     kwargs              self mins   conv to set minute          self hours   conv to set hour          self days   conv to set day          self months   conv to set month          self daysofweek   conv to set daysofweek          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t1              Return True if this event should trigger at the specified datetime            return   t1 minute     in self mins  and                  t1 hour       in self hours  and                  t1 day        in self days  and                  t1 month      in self months  and                  t1 weekday    in self daysofweek        def check self  t              Check and run action if needed             if self matchtime t               self action  self args    self kwargs   class CronTab object          The crontab implementation         def   init   self   events           self events   events      def  check self              Check all events in separate greenlets             t1   datetime  datetime now   timetuple    5           for event in self events              gevent spawn event check  t1           t1    timedelta minutes 1          s1    t1 - datetime now    seconds   1         print  Checking again in  s seconds    s1         job   gevent spawn later s1  self  check       def run self              Run the cron forever             self  check           while True              gevent sleep 60   import os  def test task           Just an example that sends a bell and asd to all terminals         os system  echo asd   wall      cron   CronTab    Event test task  22  1      Event test task  0  range 9 18 2   daysofweek range 0 5      cron run

User · Answer

I don t know if something like that already exists  It would be easy to write your own with time  datetime and or calendar modules  see http   docs python org library time html  The only concern for a python solution is that your job needs to be always running and possibly be automatically  resurrected  after a reboot  something for which you do need to rely on system dependent solutions

User · Answer

If you re looking for something lightweight checkout schedule   import schedule import time  def job        print  I m working       schedule every 10  minutes do job  schedule every   hour do job  schedule every   day at  10 30   do job   while 1      schedule run pending       time sleep 1    Disclosure  I m the author of that library

User · Answer

I like how the pycron package solves this problem  import pycron import time  while True      if pycron is now  0 2     0        True Every Sunday at 02 00         print  running backup           time sleep 60                  The process should take at least 60 sec                                        to avoid running twice in one minute     else          time sleep 15                  Check again in 15 seconds

User · Answer

You could just use normal Python argument passing syntax to specify your crontab   For example  suppose we define an Event class as below   from datetime import datetime  timedelta import time    Some utility classes   functions first class AllMatch set          Universal set - match everything        def   contains   self  item   return True  allMatch   AllMatch    def conv to set obj      Allow single integer to be provided     if isinstance obj   int long            return set  obj      Single item     if not isinstance obj  set           obj   set obj      return obj    The actual Event class class Event object       def   init   self  action  min allMatch  hour allMatch                          day allMatch  month allMatch  dow allMatch                          args     kwargs              self mins   conv to set min          self hours  conv to set hour          self days   conv to set day          self months   conv to set month          self dow   conv to set dow          self action   action         self args   args         self kwargs   kwargs      def matchtime self  t              Return True if this event should trigger at the specified datetime            return   t minute     in self mins  and                  t hour       in self hours  and                  t day        in self days  and                  t month      in self months  and                  t weekday    in self dow        def check self  t           if self matchtime t               self action  self args    self kwargs     Note  Not thoroughly tested   Then your CronTab can be specified in normal python syntax as   c   CronTab    Event perform backup  0  2  dow 6      Event purge temps  0  range 9 18 2   dow range 0 5       This way you get the full power of Python s argument mechanics  mixing positional and keyword args  and can use symbolic names for names of weeks and months   The CronTab class would be defined as simply sleeping in minute increments  and calling check   on each event    There are probably some subtleties with daylight savings time   timezones to be wary of though    Here s a quick implementation   class CronTab object       def   init   self   events           self events   events      def run self           t datetime  datetime now   timetuple    5           while 1              for e in self events                  e check t               t    timedelta minutes 1              while datetime now    lt  t                  time sleep  t - datetime now    seconds    A few things to note   Python s weekdays   months are zero indexed  unlike cron   and that range excludes the last element  hence syntax like  1-5  becomes range 0 5  - ie  0 1 2 3 4    If you prefer cron syntax  parsing it shouldn t be too difficult however

User · Answer

If you re looking for something lightweight checkout schedule   import schedule import time  def job        print  I m working       schedule every 10  minutes do job  schedule every   hour do job  schedule every   day at  10 30   do job   while 1      schedule run pending       time sleep 1    Disclosure  I m the author of that library

User · Answer

None of the listed solutions even attempt to parse a complex cron schedule string  So  here is my version  using croniter  Basic gist   schedule      5            Run every five minutes  nextRunTime   getNextCronRunTime schedule  while True       roundedDownTime   roundDownTime        if  roundedDownTime    nextRunTime                                                              Do your periodic thing here                                                             nextRunTime   getNextCronRunTime schedule       elif  roundedDownTime  gt  nextRunTime              We missed an execution  Error  Re initialize           nextRunTime   getNextCronRunTime schedule       sleepTillTopOfNextMinute     Helper routines   from croniter import croniter from datetime import datetime  timedelta    Round time down to the top of the previous minute def roundDownTime dt None  dateDelta timedelta minutes 1        roundTo   dateDelta total seconds       if dt    None   dt   datetime now       seconds    dt - dt min  seconds     rounding    seconds roundTo 2     roundTo   roundTo     return dt   timedelta 0 rounding-seconds -dt microsecond     Get next run time from now  based on schedule specified by cron string def getNextCronRunTime schedule       return croniter schedule  datetime now    get next datetime     Sleep till the top of the next minute def sleepTillTopOfNextMinute        t   datetime utcnow       sleeptime   60 -  t second   t microsecond 1000000 0      time sleep sleeptime

[python] How do I get a Cron like scheduler in Python?

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