Reimport a module while interactive
Question:
How do I reimport a module? I want to reimport a module after making changes to its .py file.
Answers:
For Python 3.4+:
import importlib
importlib.reload(nameOfModule)
For Python < 3.4:
reload(my.module)
From the Python docs
Reload a previously imported module. The argument must be a module object, so it must have been successfully imported before. This is useful if you have edited the module source file using an external editor and want to try out the new version without leaving the Python interpreter.
Don’t forget the caveats of using this method:
-
When a module is reloaded, its dictionary (containing the module’s global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem, but if the new version of a module does not define a name that was defined by the old version, the old definition is not removed.
-
If a module imports objects from another module using from ... import ..., calling reload() for the other module does not redefine the objects imported from it — one way around this is to re-execute the from statement, another is to use import and qualified names (module.*name*) instead.
-
If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances — they continue to use the old class definition. The same is true for derived classes.
In python 3, reload is no longer a built in function.
If you are using python 3.4+ you should use reload from the importlib library instead:
import importlib
importlib.reload(some_module)
If you are using python 3.2 or 3.3 you should:
import imp
imp.reload(module)
instead. See http://docs.python.org/3.0/library/imp.html#imp.reload
If you are using ipython, definitely consider using the autoreload extension:
%load_ext autoreload
%autoreload 2
Actually, in Python 3 the module imp is marked as DEPRECATED. Well, at least that’s true for 3.4.
Instead the reload function from the importlib module should be used:
https://docs.python.org/3/library/importlib.html#importlib.reload
But be aware that this library had some API-changes with the last two minor versions.
Although the provided answers do work for a specific module, they won’t reload submodules, as noted in This answer:
If a module imports objects from another module using from ... import ..., calling reload() for the other module does not redefine the objects imported from it — one way around this is to re-execute the from statement, another is to use import and qualified names (module.*name*) instead.
However, if using the __all__ variable to define the public API, it is possible to automatically reload all publicly available modules:
# Python >= 3.5
import importlib
import types
def walk_reload(module: types.ModuleType) -> None:
if hasattr(module, "__all__"):
for submodule_name in module.__all__:
walk_reload(getattr(module, submodule_name))
importlib.reload(module)
walk_reload(my_module)
The caveats noted in the previous answer are still valid though. Notably, modifying a submodule that is not part of the public API as described by the __all__ variable won’t be affected by a reload using this function. Similarly, removing an element of a submodule won’t be reflected by a reload.
If you want to import a specific function or class from a module, you can do this:
import importlib
import sys
importlib.reload(sys.modules['my_module'])
from my_module import my_function
Another small point: If you used the import some_module as sm syntax, then you have to re-load the module with its aliased name (sm in this example):
>>> import some_module as sm
...
>>> import importlib
>>> importlib.reload(some_module) # raises "NameError: name 'some_module' is not defined"
>>> importlib.reload(sm) # works
import sys
del sys.modules['module_name']
import module_name
How do I reimport a module? I want to reimport a module after making changes to its .py file.
For Python 3.4+:
import importlib
importlib.reload(nameOfModule)
For Python < 3.4:
reload(my.module)
From the Python docs
Reload a previously imported module. The argument must be a module object, so it must have been successfully imported before. This is useful if you have edited the module source file using an external editor and want to try out the new version without leaving the Python interpreter.
Don’t forget the caveats of using this method:
-
When a module is reloaded, its dictionary (containing the module’s global variables) is retained. Redefinitions of names will override the old definitions, so this is generally not a problem, but if the new version of a module does not define a name that was defined by the old version, the old definition is not removed.
-
If a module imports objects from another module using
from ... import ..., callingreload()for the other module does not redefine the objects imported from it — one way around this is to re-execute thefromstatement, another is to useimportand qualified names (module.*name*) instead. -
If a module instantiates instances of a class, reloading the module that defines the class does not affect the method definitions of the instances — they continue to use the old class definition. The same is true for derived classes.
In python 3, reload is no longer a built in function.
If you are using python 3.4+ you should use reload from the importlib library instead:
import importlib
importlib.reload(some_module)
If you are using python 3.2 or 3.3 you should:
import imp
imp.reload(module)
instead. See http://docs.python.org/3.0/library/imp.html#imp.reload
If you are using ipython, definitely consider using the autoreload extension:
%load_ext autoreload
%autoreload 2
Actually, in Python 3 the module imp is marked as DEPRECATED. Well, at least that’s true for 3.4.
Instead the reload function from the importlib module should be used:
https://docs.python.org/3/library/importlib.html#importlib.reload
But be aware that this library had some API-changes with the last two minor versions.
Although the provided answers do work for a specific module, they won’t reload submodules, as noted in This answer:
If a module imports objects from another module using
from ... import ..., callingreload()for the other module does not redefine the objects imported from it — one way around this is to re-execute the from statement, another is to useimportand qualified names (module.*name*) instead.
However, if using the __all__ variable to define the public API, it is possible to automatically reload all publicly available modules:
# Python >= 3.5
import importlib
import types
def walk_reload(module: types.ModuleType) -> None:
if hasattr(module, "__all__"):
for submodule_name in module.__all__:
walk_reload(getattr(module, submodule_name))
importlib.reload(module)
walk_reload(my_module)
The caveats noted in the previous answer are still valid though. Notably, modifying a submodule that is not part of the public API as described by the __all__ variable won’t be affected by a reload using this function. Similarly, removing an element of a submodule won’t be reflected by a reload.
If you want to import a specific function or class from a module, you can do this:
import importlib
import sys
importlib.reload(sys.modules['my_module'])
from my_module import my_function
Another small point: If you used the import some_module as sm syntax, then you have to re-load the module with its aliased name (sm in this example):
>>> import some_module as sm
...
>>> import importlib
>>> importlib.reload(some_module) # raises "NameError: name 'some_module' is not defined"
>>> importlib.reload(sm) # works
import sys
del sys.modules['module_name']
import module_name