Reimport a module while interactive

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

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

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.

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

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're already in interactive and have waited for long-running code, and you need to reload something you imported using from mod import func and it would take a long time to re-run all the previous cells, this is the solution I found:

import importlib
import mod

importlib.reload(mod)

func = mod.func

This will reassign the previously loaded function with the new version and not require you to change your function calls to include the module name. Thereafter, you should just be able to reload the module again and reassign the function every time you make edits.

import sys

del sys.modules['module_name']
import module_name