How do I unload reload a Python module

Question

I have a long-running Python server and would like to be able to upgrade a service without restarting the server  What s the best way do do this   if foo py has changed      unimport foo   lt -- How do I do this      import foo     myfoo   foo Foo

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Other option  See that Python default importlib reload will just reimport the library passed as an argument  It won t reload the libraries that your lib import  If you changed a lot of files and have a somewhat complex package to import  you must do a deep reload    If you have IPython or Jupyter installed  you can use a function to deep reload all libs   from IPython lib deepreload import reload as dreload dreload foo    If you don t have Jupyter  install it with this command in your shell   pip3 install jupyter

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For those like me who want to unload all modules  when running in the Python interpreter under Emacs       for mod in sys modules values          reload mod    More information is in Reloading Python modules

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Another way could be to import the module in a function  This way when the function completes the module gets garbage collected

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if  myModule  in sys modules        del sys modules  myModule

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I got a lot of trouble trying to reload something inside Sublime Text  but finally I could wrote this utility to reload modules on Sublime Text based on the code sublime plugin py uses to reload modules   This below accepts you to reload modules from paths with spaces on their names  then later after reloading you can just import as you usually do   def reload module full module name                   Assuming the folder  full module name  is a folder inside some         folder on the python sys path  for example  sys path as  C     and         you are inside the folder  C  Path With Spaces  on the file           C  Path With Spaces main py  and want to re-import some files on         the folder  C  Path With Spaces tests            param full module name   the relative full path to the module file                                   you want to reload from a folder on the                                   python  sys path              import imp     import sys     import importlib      if full module name in sys modules          module object   sys modules full module name          module object   imp reload  module object        else          importlib import module  full module name    def run tests        print    n n        reload module   Path With Spaces tests semantic linefeed unit tests        reload module   Path With Spaces tests semantic linefeed manual tests         from  tests import semantic linefeed unit tests     from  tests import semantic linefeed manual tests      semantic linefeed unit tests run unit tests       semantic linefeed manual tests run manual tests    if   name         main         run tests     If you run for the first time  this should load the module  but if later you can again the method function run tests   it will reload the tests files  With Sublime Text  Python 3 3 6  this happens a lot because its interpreter never closes  unless you restart Sublime Text  i e   the Python3 3 interpreter

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In Python 3 0   3 3 you would use  imp reload module   The BDFL has answered this question   However  imp was deprecated in 3 4  in favour of importlib  thanks  Stefan     I think  therefore  you   d now use importlib reload module   although I   m not sure

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Enthought Traits has a module that works fairly well for this  https   traits readthedocs org en 4 3 0  modules traits util refresh html  It will reload any module that has been changed  and update other modules and instanced objects that are using it  It does not work most of the time with   very private   methods  and can choke on class inheritance  but it saves me crazy amounts of time from having to restart the host application when writing PyQt guis  or stuff that runs inside programs such as Maya or Nuke  It doesn t work maybe 20-30   of the time  but it s still incredibly helpful   Enthought s package doesn t reload files the moment they change - you have to call it explicitely - but that shouldn t be all that hard to implement if you really need it

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For Python 2 use built-in function reload     reload module    For Python 2 and 3 2   3 3 use reload from module imp   import imp imp reload module    But imp is  deprecated since version 3 4 in favor of importlib  so use   import importlib importlib reload module    or  from importlib import reload reload module

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The following code allows you Python 2 3 compatibility   try      reload except NameError        Python 3     from imp import reload   The you can use it as reload   in both versions which makes things simpler

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Those who are using python 3 and reload from importlib   If you have problems like it seems that module doesn t reload    That is because it needs some time to recompile pyc  up to 60 sec  I writing this hint just that you know if you have experienced this kind of problem

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If you are not in a server  but developing and need to frequently reload a module  here s a nice tip  First  make sure you are using the excellent IPython shell  from the Jupyter Notebook project  After installing Jupyter  you can start it with ipython  or jupyter console  or even better  jupyter qtconsole  which will give you a nice colorized console with code completion in any OS  Now in your shell  type   load ext autoreload  autoreload 2  Now  every time you run your script  your modules will be reloaded  Beyond the 2  there are other options of the autoreload magic   autoreload Reload all modules  except those excluded by  aimport  automatically now    autoreload 0 Disable automatic reloading    autoreload 1 Reload all modules imported with  aimport every time before executing the Python code typed    autoreload 2 Reload all modules  except those excluded by  aimport  every time before executing the Python code typed   Sure  it will also work on a Jupyter Notebook

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reload module   but only if it s completely stand-alone  If anything else has a reference to the module  or any object belonging to the module   then you ll get subtle and curious errors caused by the old code hanging around longer than you expected  and things like isinstance not working across different versions of the same code  If you have one-way dependencies  you must also reload all modules that depend on the reloaded module to get rid of all the references to the old code  And then reload modules that depend on the reloaded modules  recursively  If you have circular dependencies  which is very common for example when you are dealing with reloading a package  you must unload all the modules in the group in one go  You can t do this with reload   because it will re-import each module before its dependencies have been refreshed  allowing old references to creep into new modules  The only way to do it in this case is to hack sys modules  which is kind of unsupported  You d have to go through and delete each sys modules entry you wanted to be reloaded on next import  and also delete entries whose values are None to deal with an implementation issue to do with caching failed relative imports  It s not terribly nice but as long as you have a fully self-contained set of dependencies that doesn t leave references outside its codebase  it s workable  It s probably best to restart the server   -

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If you encounter the following error  this answer may help you to get a solution   Traceback  most recent call last     File  FFFF   line 1  in   NameError  name  YYYY  is not defined  OR  Traceback  most recent call last    File  FFFF   line 1  in   File   usr local lib python3 7 importlib   init   py   line 140  in reload    raise TypeError  reload   argument must be a module   TypeError  reload   argument must be a module  In case you have an import like the one below  you may need to use the sys modules to get the module you want to reload    import importlib   import sys    from YYYY XXX ZZZ import CCCC   import AAA BBB CC     def reload full name      if full name in sys modules        importlib reload sys modules full name       reload  YYYY XXX ZZZ     this is fine in both cases   reload  AAA BBB CC        importlib reload YYYY XXX ZZZ    in my case  this fails   importlib reload AAA BBB CC                  and this is ok   The main issue is that the importlib reload accepts module only not string

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Enthought Traits has a module that works fairly well for this  https   traits readthedocs org en 4 3 0  modules traits util refresh html  It will reload any module that has been changed  and update other modules and instanced objects that are using it  It does not work most of the time with   very private   methods  and can choke on class inheritance  but it saves me crazy amounts of time from having to restart the host application when writing PyQt guis  or stuff that runs inside programs such as Maya or Nuke  It doesn t work maybe 20-30   of the time  but it s still incredibly helpful   Enthought s package doesn t reload files the moment they change - you have to call it explicitely - but that shouldn t be all that hard to implement if you really need it

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If you encounter the following error  this answer may help you to get a solution   Traceback  most recent call last     File  FFFF   line 1  in   NameError  name  YYYY  is not defined  OR  Traceback  most recent call last    File  FFFF   line 1  in   File   usr local lib python3 7 importlib   init   py   line 140  in reload    raise TypeError  reload   argument must be a module   TypeError  reload   argument must be a module  In case you have an import like the one below  you may need to use the sys modules to get the module you want to reload    import importlib   import sys    from YYYY XXX ZZZ import CCCC   import AAA BBB CC     def reload full name      if full name in sys modules        importlib reload sys modules full name       reload  YYYY XXX ZZZ     this is fine in both cases   reload  AAA BBB CC        importlib reload YYYY XXX ZZZ    in my case  this fails   importlib reload AAA BBB CC                  and this is ok   The main issue is that the importlib reload accepts module only not string

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reload module   but only if it s completely stand-alone  If anything else has a reference to the module  or any object belonging to the module   then you ll get subtle and curious errors caused by the old code hanging around longer than you expected  and things like isinstance not working across different versions of the same code  If you have one-way dependencies  you must also reload all modules that depend on the reloaded module to get rid of all the references to the old code  And then reload modules that depend on the reloaded modules  recursively  If you have circular dependencies  which is very common for example when you are dealing with reloading a package  you must unload all the modules in the group in one go  You can t do this with reload   because it will re-import each module before its dependencies have been refreshed  allowing old references to creep into new modules  The only way to do it in this case is to hack sys modules  which is kind of unsupported  You d have to go through and delete each sys modules entry you wanted to be reloaded on next import  and also delete entries whose values are None to deal with an implementation issue to do with caching failed relative imports  It s not terribly nice but as long as you have a fully self-contained set of dependencies that doesn t leave references outside its codebase  it s workable  It s probably best to restart the server   -

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You can reload a module when it has already been imported by using the reload builtin function  Python 3 4  only    from importlib import reload   import foo  while True        Do some things      if is changed foo           foo   reload foo    In Python 3  reload was moved to the imp module  In 3 4  imp was deprecated in favor of importlib  and reload was added to the latter  When targeting 3 or later  either reference the appropriate module when calling reload or import it   I think that this is what you want  Web servers like Django s development server use this so that you can see the effects of your code changes without restarting the server process itself   To quote from the docs      Python modules    code is recompiled and   the module-level code reexecuted    defining a new set of objects which   are bound to names in the module   s   dictionary  The init function of   extension modules is not called a   second time  As with all other objects   in Python the old objects are only   reclaimed after their reference counts   drop to zero  The names in the module   namespace are updated to point to any   new or changed objects  Other   references to the old objects  such as   names external to the module  are not   rebound to refer to the new objects   and must be updated in each namespace   where they occur if that is desired    As you noted in your question  you ll have to reconstruct Foo objects if the Foo class resides in the foo module

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For those like me who want to unload all modules  when running in the Python interpreter under Emacs       for mod in sys modules values          reload mod    More information is in Reloading Python modules

User · Answer

You can reload a module when it has already been imported by using the reload builtin function  Python 3 4  only    from importlib import reload   import foo  while True        Do some things      if is changed foo           foo   reload foo    In Python 3  reload was moved to the imp module  In 3 4  imp was deprecated in favor of importlib  and reload was added to the latter  When targeting 3 or later  either reference the appropriate module when calling reload or import it   I think that this is what you want  Web servers like Django s development server use this so that you can see the effects of your code changes without restarting the server process itself   To quote from the docs      Python modules    code is recompiled and   the module-level code reexecuted    defining a new set of objects which   are bound to names in the module   s   dictionary  The init function of   extension modules is not called a   second time  As with all other objects   in Python the old objects are only   reclaimed after their reference counts   drop to zero  The names in the module   namespace are updated to point to any   new or changed objects  Other   references to the old objects  such as   names external to the module  are not   rebound to refer to the new objects   and must be updated in each namespace   where they occur if that is desired    As you noted in your question  you ll have to reconstruct Foo objects if the Foo class resides in the foo module

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Those who are using python 3 and reload from importlib   If you have problems like it seems that module doesn t reload    That is because it needs some time to recompile pyc  up to 60 sec  I writing this hint just that you know if you have experienced this kind of problem

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reload module   but only if it s completely stand-alone  If anything else has a reference to the module  or any object belonging to the module   then you ll get subtle and curious errors caused by the old code hanging around longer than you expected  and things like isinstance not working across different versions of the same code  If you have one-way dependencies  you must also reload all modules that depend on the reloaded module to get rid of all the references to the old code  And then reload modules that depend on the reloaded modules  recursively  If you have circular dependencies  which is very common for example when you are dealing with reloading a package  you must unload all the modules in the group in one go  You can t do this with reload   because it will re-import each module before its dependencies have been refreshed  allowing old references to creep into new modules  The only way to do it in this case is to hack sys modules  which is kind of unsupported  You d have to go through and delete each sys modules entry you wanted to be reloaded on next import  and also delete entries whose values are None to deal with an implementation issue to do with caching failed relative imports  It s not terribly nice but as long as you have a fully self-contained set of dependencies that doesn t leave references outside its codebase  it s workable  It s probably best to restart the server   -

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for me for case of Abaqus it is the way it works  Imagine your file is Class VerticesEdges py  sys path append  D      My Pythons   if  Class VerticesEdges  in sys modules        del sys modules  Class VerticesEdges       print  old module Class VerticesEdges deleted  from Class VerticesEdges import   reload sys modules  Class VerticesEdges

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if  myModule  in sys modules        del sys modules  myModule

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In Python 3 0   3 3 you would use  imp reload module   The BDFL has answered this question   However  imp was deprecated in 3 4  in favour of importlib  thanks  Stefan     I think  therefore  you   d now use importlib reload module   although I   m not sure

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The following code allows you Python 2 3 compatibility   try      reload except NameError        Python 3     from imp import reload   The you can use it as reload   in both versions which makes things simpler

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Another way could be to import the module in a function  This way when the function completes the module gets garbage collected

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This is the modern way of reloading a module   from importlib import reload   If you want to support versions of Python older than 3 5  try this   from sys import version info if version info 0   lt  3      pass   Python 2 has built in reload elif version info 0     3 and version info 1   lt   4      from imp import reload   Python 3 0 - 3 4  else      from importlib import reload   Python 3 5    To use it  run reload MODULE   replacing MODULE with the module you want to reload   For example  reload math  will reload the math module

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You can reload a module when it has already been imported by using the reload builtin function  Python 3 4  only    from importlib import reload   import foo  while True        Do some things      if is changed foo           foo   reload foo    In Python 3  reload was moved to the imp module  In 3 4  imp was deprecated in favor of importlib  and reload was added to the latter  When targeting 3 or later  either reference the appropriate module when calling reload or import it   I think that this is what you want  Web servers like Django s development server use this so that you can see the effects of your code changes without restarting the server process itself   To quote from the docs      Python modules    code is recompiled and   the module-level code reexecuted    defining a new set of objects which   are bound to names in the module   s   dictionary  The init function of   extension modules is not called a   second time  As with all other objects   in Python the old objects are only   reclaimed after their reference counts   drop to zero  The names in the module   namespace are updated to point to any   new or changed objects  Other   references to the old objects  such as   names external to the module  are not   rebound to refer to the new objects   and must be updated in each namespace   where they occur if that is desired    As you noted in your question  you ll have to reconstruct Foo objects if the Foo class resides in the foo module

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I got a lot of trouble trying to reload something inside Sublime Text  but finally I could wrote this utility to reload modules on Sublime Text based on the code sublime plugin py uses to reload modules   This below accepts you to reload modules from paths with spaces on their names  then later after reloading you can just import as you usually do   def reload module full module name                   Assuming the folder  full module name  is a folder inside some         folder on the python sys path  for example  sys path as  C     and         you are inside the folder  C  Path With Spaces  on the file           C  Path With Spaces main py  and want to re-import some files on         the folder  C  Path With Spaces tests            param full module name   the relative full path to the module file                                   you want to reload from a folder on the                                   python  sys path              import imp     import sys     import importlib      if full module name in sys modules          module object   sys modules full module name          module object   imp reload  module object        else          importlib import module  full module name    def run tests        print    n n        reload module   Path With Spaces tests semantic linefeed unit tests        reload module   Path With Spaces tests semantic linefeed manual tests         from  tests import semantic linefeed unit tests     from  tests import semantic linefeed manual tests      semantic linefeed unit tests run unit tests       semantic linefeed manual tests run manual tests    if   name         main         run tests     If you run for the first time  this should load the module  but if later you can again the method function run tests   it will reload the tests files  With Sublime Text  Python 3 3 6  this happens a lot because its interpreter never closes  unless you restart Sublime Text  i e   the Python3 3 interpreter

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If you are not in a server  but developing and need to frequently reload a module  here s a nice tip  First  make sure you are using the excellent IPython shell  from the Jupyter Notebook project  After installing Jupyter  you can start it with ipython  or jupyter console  or even better  jupyter qtconsole  which will give you a nice colorized console with code completion in any OS  Now in your shell  type   load ext autoreload  autoreload 2  Now  every time you run your script  your modules will be reloaded  Beyond the 2  there are other options of the autoreload magic   autoreload Reload all modules  except those excluded by  aimport  automatically now    autoreload 0 Disable automatic reloading    autoreload 1 Reload all modules imported with  aimport every time before executing the Python code typed    autoreload 2 Reload all modules  except those excluded by  aimport  every time before executing the Python code typed   Sure  it will also work on a Jupyter Notebook

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reload module   but only if it s completely stand-alone  If anything else has a reference to the module  or any object belonging to the module   then you ll get subtle and curious errors caused by the old code hanging around longer than you expected  and things like isinstance not working across different versions of the same code  If you have one-way dependencies  you must also reload all modules that depend on the reloaded module to get rid of all the references to the old code  And then reload modules that depend on the reloaded modules  recursively  If you have circular dependencies  which is very common for example when you are dealing with reloading a package  you must unload all the modules in the group in one go  You can t do this with reload   because it will re-import each module before its dependencies have been refreshed  allowing old references to creep into new modules  The only way to do it in this case is to hack sys modules  which is kind of unsupported  You d have to go through and delete each sys modules entry you wanted to be reloaded on next import  and also delete entries whose values are None to deal with an implementation issue to do with caching failed relative imports  It s not terribly nice but as long as you have a fully self-contained set of dependencies that doesn t leave references outside its codebase  it s workable  It s probably best to restart the server   -

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The accepted answer doesn t handle the from X import Y case  This code handles it and the standard import case as well   def importOrReload module name   names       import sys      if module name in sys modules          reload sys modules module name       else            import   module name  fromlist names       for name in names          globals   name    getattr sys modules module name   name     use instead of  from dfly parser import parseMessages importOrReload  dfly parser    parseMessages     In the reloading case  we reassign the top level names to the values stored in the newly reloaded module  which updates them

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Removing modules from sys modules requires  None  types to be deleted as well  Method 1  import sys import json      your module  for mod in   m for m in sys modules if m lstrip      startswith  json   or sys modules m     None    del sys modules mod   print  json dumps   1           test if functionality has been removed  Method 2  using bookkeeping entries  to remove all dependencies  import sys  before import    mod for mod in sys modules  import json      your module after import    mod for mod in sys modules if mod not in before import   for mod in  m for m in sys modules if m in after import or sys modules m     None   del sys modules mod   print  json dumps   2           test if functionality has been removed  Optional  just to be certain all entries are out  if you so choose  import gc gc collect

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It can be especially difficult to delete a module if it is not pure Python   Here is some information from  How do I really delete an imported module      You can use sys getrefcount   to find out the actual number of   references     gt  gt  gt  import sys  empty  os  gt  gt  gt  sys getrefcount sys  9  gt  gt  gt  sys getrefcount os  6  gt  gt  gt  sys getrefcount empty  3      Numbers greater than 3 indicate that   it will be hard to get rid of the   module  The homegrown  empty     containing nothing  module should be   garbage collected after    gt  gt  gt  del sys modules  empty    gt  gt  gt  del empty      as the third reference is an artifact   of the getrefcount   function

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Other option  See that Python default importlib reload will just reimport the library passed as an argument  It won t reload the libraries that your lib import  If you changed a lot of files and have a somewhat complex package to import  you must do a deep reload    If you have IPython or Jupyter installed  you can use a function to deep reload all libs   from IPython lib deepreload import reload as dreload dreload foo    If you don t have Jupyter  install it with this command in your shell   pip3 install jupyter

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2018-02-01   module foo must be imported successfully in advance    from importlib import reload  reload foo       31 5  importlib     The implementation of import     Python 3 6 4 documentation

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Edit  Answer V2  The solution from before is good for just getting the reset information  but it will not change all the references  more than reload but less then required   To actually set all the references as well  I had to go into the garbage collector  and rewrite the references there  Now it works like a charm  Note that this will not work if the GC is turned off  or if reloading data that s not monitored by the GC  If you don t want to mess with the GC  the original answer might be enough for you  New code  import importlib import inspect import gc from weakref import ref   def reset module module  inner modules also True        quot  quot  quot      This function is a stronger form of importlib s  reload  function  What it does  is that aside from reloading a     module  it goes to the old instance of the module  and sets all the  not read-only  attributes  functions and classes     to be the reloaded-module s      param module  The module to reload  module reference  not the name       param inner modules also  Whether to treat ths module as a package as well  and reload all the modules within it       quot  quot  quot         For the case when the module is actually a package     if inner modules also          submods    submod for    submod in inspect getmembers module                     if  type submod    name       module   and  submod   package   startswith module   name              for submod in submods              reset module submod  True         First  log all the references before reloading  because some references may be changed by the reload operation       module tree    get tree references to reset recursively module  module   name         new module   importlib reload module       reset item recursively module  module tree  new module    def  update referrers item  new item       refs   gc get referrers item       weak ref item   ref item      for coll in refs          if type coll     dict              enumerator   coll keys           elif type coll     list              enumerator   range len coll           else              continue          for key in enumerator               if weak ref item   is None                    No refs are left in the GC                 return              if coll key  is weak ref item                    coll key    new item  def  get tree references to reset recursively item  module name  grayed out item ids   None       if grayed out item ids is None          grayed out item ids   set        item tree   dict       attr names   set dir item   -  readonly attrs     for sub item name in attr names           sub item   getattr item  sub item name          item tree sub item name     sub item  None           try                Will work for classes and functions defined in that module              mod name   sub item   module           except AttributeError              mod name   None            If this item was defined within this module  deep-reset         if  mod name is None  or  mod name    module name  or  id sub item  in grayed out item ids                    or isinstance sub item  EnumMeta               continue          grayed out item ids add id sub item           item tree sub item name  1                   get tree references to reset recursively sub item  module name  grayed out item ids       return item tree   def  reset item recursively item  item subtree  new item          Set children first so we don t lose the current references      if item subtree is not None          for sub item name   sub item  sub item tree  in item subtree items                 try                  new sub item   getattr new item  sub item name              except AttributeError                    The item doesn t exist in the reloaded module  Ignore                  continue              try                    Set the item                  reset item recursively sub item  sub item tree  new sub item              except Exception as ex                  pass       update referrers item  new item   Original Answer As written in  bobince s answer  if there s already a reference to that module in another module  especially if it was imported with the as keyword like import numpy as np   that instance will not be overwritten  This proved quite problematic to me when applying tests that required a  quot clean-slate quot  state of the configuration modules  so I ve written a function named reset module that uses importlib s reload function and recursively overwrites all the declared module s attributes  It has been tested with Python version 3 6  import importlib import inspect from enum import EnumMeta   readonly attrs       annotations        call        class        closure        code        defaults        delattr                       dict        dir        doc        eq        format        func        ge        get                       getattribute        globals        gt        hash        init        init subclass                       kwdefaults        le        lt        module        name        ne        new        qualname                       reduce        reduce ex        repr        self        setattr        sizeof        str                       subclasshook        weakref        members        mro        itemsize        isabstractmethod                       basicsize        base       def reset module module  inner modules also True        quot  quot  quot      This function is a stronger form of importlib s  reload  function  What it does  is that aside from reloading a     module  it goes to the old instance of the module  and sets all the  not read-only  attributes  functions and classes     to be the reloaded-module s      param module  The module to reload  module reference  not the name       param inner modules also  Whether to treat ths module as a package as well  and reload all the modules within it       quot  quot  quot       new module   importlib reload module       reset items   set          For the case when the module is actually a package     if inner modules also          submods    submod for    submod in inspect getmembers module                     if  type submod    name       module   and  submod   package   startswith module   name              for submod in submods              reset module submod  True        reset item recursively module  new module  module   name    reset items    def  reset item recursively item  new item  module name  reset items None       if reset items is None          reset items   set        attr names   set dir item   -  readonly attrs      for sitem name in attr names           sitem   getattr item  sitem name          new sitem   getattr new item  sitem name           try                Set the item             setattr item  sitem name  new sitem               try                    Will work for classes and functions defined in that module                  mod name   sitem   module               except AttributeError                  mod name   None                If this item was defined within this module  deep-reset             if  mod name is None  or  mod name    module name  or  id sitem  in reset items                        or isinstance sitem  EnumMeta      Deal with enums                 continue              reset items add id sitem                reset item recursively sitem  new sitem  module name  reset items          except Exception as ex              raise Exception sitem name  from ex  Note  Use with care  Using these on non-peripheral modules  modules that define externally-used classes  for example  might lead to internal problems in Python  such as pickling un-pickling issues

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This is the modern way of reloading a module   from importlib import reload   If you want to support versions of Python older than 3 5  try this   from sys import version info if version info 0   lt  3      pass   Python 2 has built in reload elif version info 0     3 and version info 1   lt   4      from imp import reload   Python 3 0 - 3 4  else      from importlib import reload   Python 3 5    To use it  run reload MODULE   replacing MODULE with the module you want to reload   For example  reload math  will reload the math module

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For Python 2 use built-in function reload     reload module    For Python 2 and 3 2   3 3 use reload from module imp   import imp imp reload module    But imp is  deprecated since version 3 4 in favor of importlib  so use   import importlib importlib reload module    or  from importlib import reload reload module

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You can reload a module when it has already been imported by using the reload builtin function  Python 3 4  only    from importlib import reload   import foo  while True        Do some things      if is changed foo           foo   reload foo    In Python 3  reload was moved to the imp module  In 3 4  imp was deprecated in favor of importlib  and reload was added to the latter  When targeting 3 or later  either reference the appropriate module when calling reload or import it   I think that this is what you want  Web servers like Django s development server use this so that you can see the effects of your code changes without restarting the server process itself   To quote from the docs      Python modules    code is recompiled and   the module-level code reexecuted    defining a new set of objects which   are bound to names in the module   s   dictionary  The init function of   extension modules is not called a   second time  As with all other objects   in Python the old objects are only   reclaimed after their reference counts   drop to zero  The names in the module   namespace are updated to point to any   new or changed objects  Other   references to the old objects  such as   names external to the module  are not   rebound to refer to the new objects   and must be updated in each namespace   where they occur if that is desired    As you noted in your question  you ll have to reconstruct Foo objects if the Foo class resides in the foo module

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Removing modules from sys modules requires  None  types to be deleted as well  Method 1  import sys import json      your module  for mod in   m for m in sys modules if m lstrip      startswith  json   or sys modules m     None    del sys modules mod   print  json dumps   1           test if functionality has been removed  Method 2  using bookkeeping entries  to remove all dependencies  import sys  before import    mod for mod in sys modules  import json      your module after import    mod for mod in sys modules if mod not in before import   for mod in  m for m in sys modules if m in after import or sys modules m     None   del sys modules mod   print  json dumps   2           test if functionality has been removed  Optional  just to be certain all entries are out  if you so choose  import gc gc collect

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Edit  Answer V2  The solution from before is good for just getting the reset information  but it will not change all the references  more than reload but less then required   To actually set all the references as well  I had to go into the garbage collector  and rewrite the references there  Now it works like a charm  Note that this will not work if the GC is turned off  or if reloading data that s not monitored by the GC  If you don t want to mess with the GC  the original answer might be enough for you  New code  import importlib import inspect import gc from weakref import ref   def reset module module  inner modules also True        quot  quot  quot      This function is a stronger form of importlib s  reload  function  What it does  is that aside from reloading a     module  it goes to the old instance of the module  and sets all the  not read-only  attributes  functions and classes     to be the reloaded-module s      param module  The module to reload  module reference  not the name       param inner modules also  Whether to treat ths module as a package as well  and reload all the modules within it       quot  quot  quot         For the case when the module is actually a package     if inner modules also          submods    submod for    submod in inspect getmembers module                     if  type submod    name       module   and  submod   package   startswith module   name              for submod in submods              reset module submod  True         First  log all the references before reloading  because some references may be changed by the reload operation       module tree    get tree references to reset recursively module  module   name         new module   importlib reload module       reset item recursively module  module tree  new module    def  update referrers item  new item       refs   gc get referrers item       weak ref item   ref item      for coll in refs          if type coll     dict              enumerator   coll keys           elif type coll     list              enumerator   range len coll           else              continue          for key in enumerator               if weak ref item   is None                    No refs are left in the GC                 return              if coll key  is weak ref item                    coll key    new item  def  get tree references to reset recursively item  module name  grayed out item ids   None       if grayed out item ids is None          grayed out item ids   set        item tree   dict       attr names   set dir item   -  readonly attrs     for sub item name in attr names           sub item   getattr item  sub item name          item tree sub item name     sub item  None           try                Will work for classes and functions defined in that module              mod name   sub item   module           except AttributeError              mod name   None            If this item was defined within this module  deep-reset         if  mod name is None  or  mod name    module name  or  id sub item  in grayed out item ids                    or isinstance sub item  EnumMeta               continue          grayed out item ids add id sub item           item tree sub item name  1                   get tree references to reset recursively sub item  module name  grayed out item ids       return item tree   def  reset item recursively item  item subtree  new item          Set children first so we don t lose the current references      if item subtree is not None          for sub item name   sub item  sub item tree  in item subtree items                 try                  new sub item   getattr new item  sub item name              except AttributeError                    The item doesn t exist in the reloaded module  Ignore                  continue              try                    Set the item                  reset item recursively sub item  sub item tree  new sub item              except Exception as ex                  pass       update referrers item  new item   Original Answer As written in  bobince s answer  if there s already a reference to that module in another module  especially if it was imported with the as keyword like import numpy as np   that instance will not be overwritten  This proved quite problematic to me when applying tests that required a  quot clean-slate quot  state of the configuration modules  so I ve written a function named reset module that uses importlib s reload function and recursively overwrites all the declared module s attributes  It has been tested with Python version 3 6  import importlib import inspect from enum import EnumMeta   readonly attrs       annotations        call        class        closure        code        defaults        delattr                       dict        dir        doc        eq        format        func        ge        get                       getattribute        globals        gt        hash        init        init subclass                       kwdefaults        le        lt        module        name        ne        new        qualname                       reduce        reduce ex        repr        self        setattr        sizeof        str                       subclasshook        weakref        members        mro        itemsize        isabstractmethod                       basicsize        base       def reset module module  inner modules also True        quot  quot  quot      This function is a stronger form of importlib s  reload  function  What it does  is that aside from reloading a     module  it goes to the old instance of the module  and sets all the  not read-only  attributes  functions and classes     to be the reloaded-module s      param module  The module to reload  module reference  not the name       param inner modules also  Whether to treat ths module as a package as well  and reload all the modules within it       quot  quot  quot       new module   importlib reload module       reset items   set          For the case when the module is actually a package     if inner modules also          submods    submod for    submod in inspect getmembers module                     if  type submod    name       module   and  submod   package   startswith module   name              for submod in submods              reset module submod  True        reset item recursively module  new module  module   name    reset items    def  reset item recursively item  new item  module name  reset items None       if reset items is None          reset items   set        attr names   set dir item   -  readonly attrs      for sitem name in attr names           sitem   getattr item  sitem name          new sitem   getattr new item  sitem name           try                Set the item             setattr item  sitem name  new sitem               try                    Will work for classes and functions defined in that module                  mod name   sitem   module               except AttributeError                  mod name   None                If this item was defined within this module  deep-reset             if  mod name is None  or  mod name    module name  or  id sitem  in reset items                        or isinstance sitem  EnumMeta      Deal with enums                 continue              reset items add id sitem                reset item recursively sitem  new sitem  module name  reset items          except Exception as ex              raise Exception sitem name  from ex  Note  Use with care  Using these on non-peripheral modules  modules that define externally-used classes  for example  might lead to internal problems in Python  such as pickling un-pickling issues

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2018-02-01   module foo must be imported successfully in advance    from importlib import reload  reload foo       31 5  importlib     The implementation of import     Python 3 6 4 documentation

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It can be especially difficult to delete a module if it is not pure Python   Here is some information from  How do I really delete an imported module      You can use sys getrefcount   to find out the actual number of   references     gt  gt  gt  import sys  empty  os  gt  gt  gt  sys getrefcount sys  9  gt  gt  gt  sys getrefcount os  6  gt  gt  gt  sys getrefcount empty  3      Numbers greater than 3 indicate that   it will be hard to get rid of the   module  The homegrown  empty     containing nothing  module should be   garbage collected after    gt  gt  gt  del sys modules  empty    gt  gt  gt  del empty      as the third reference is an artifact   of the getrefcount   function

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It can be especially difficult to delete a module if it is not pure Python   Here is some information from  How do I really delete an imported module      You can use sys getrefcount   to find out the actual number of   references     gt  gt  gt  import sys  empty  os  gt  gt  gt  sys getrefcount sys  9  gt  gt  gt  sys getrefcount os  6  gt  gt  gt  sys getrefcount empty  3      Numbers greater than 3 indicate that   it will be hard to get rid of the   module  The homegrown  empty     containing nothing  module should be   garbage collected after    gt  gt  gt  del sys modules  empty    gt  gt  gt  del empty      as the third reference is an artifact   of the getrefcount   function

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The accepted answer doesn t handle the from X import Y case  This code handles it and the standard import case as well   def importOrReload module name   names       import sys      if module name in sys modules          reload sys modules module name       else            import   module name  fromlist names       for name in names          globals   name    getattr sys modules module name   name     use instead of  from dfly parser import parseMessages importOrReload  dfly parser    parseMessages     In the reloading case  we reassign the top level names to the values stored in the newly reloaded module  which updates them

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for me for case of Abaqus it is the way it works  Imagine your file is Class VerticesEdges py  sys path append  D      My Pythons   if  Class VerticesEdges  in sys modules        del sys modules  Class VerticesEdges       print  old module Class VerticesEdges deleted  from Class VerticesEdges import   reload sys modules  Class VerticesEdges

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It can be especially difficult to delete a module if it is not pure Python   Here is some information from  How do I really delete an imported module      You can use sys getrefcount   to find out the actual number of   references     gt  gt  gt  import sys  empty  os  gt  gt  gt  sys getrefcount sys  9  gt  gt  gt  sys getrefcount os  6  gt  gt  gt  sys getrefcount empty  3      Numbers greater than 3 indicate that   it will be hard to get rid of the   module  The homegrown  empty     containing nothing  module should be   garbage collected after    gt  gt  gt  del sys modules  empty    gt  gt  gt  del empty      as the third reference is an artifact   of the getrefcount   function

[python] How do I unload (reload) a Python module?

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