How to reload all imported modules?

To list all imported modules, you can use sys.modules.values().

import sys
sys.modules.values()

sys.modules is a dictionary that maps the string names of modules to their references.

To reload modules, you can loop over the returned list from above and call importlib.reload on each one:

import importlib
for module in sys.modules.values():
    importlib.reload(module)

I imagine in most situations, you want to reload only the modules that you yourself are editing. One reason to do this is to avoid expensive reloads, and another is hinted in @dwanderson's comment, when reloading pre-loaded modules might be sensitive to the order in which they are loaded. It's particularly problematic to reload importlib itself. Anyways, the following code reloads only the modules imported after the code is run:

PRELOADED_MODULES = set()

def init() :
    # local imports to keep things neat
    from sys import modules
    import importlib

    global PRELOADED_MODULES

    # sys and importlib are ignored here too
    PRELOADED_MODULES = set(modules.values())

def reload() :
    from sys import modules
    import importlib

    for module in set(modules.values()) - PRELOADED_MODULES :
        try :
            importlib.reload(module)
        except :
            # there are some problems that are swept under the rug here
            pass

init()

The code is not exactly correct because of the except block, but it seems robust enough for my own purposes (reloading imports in a REPL).