Hard Reload

Hi folks,

If you're a python developer this shouldn't be new for you, but I struggled a lot with this back in the day and thought it might be helpful share some of the lessons learned.

Each time you import a python module in a session it get cached in a global dictionary called sys.modules, this helps to speedup things and allow a better memory management. If you really need to refresh that cache for a specific module (because of a code change or whatever) python provides a nice function called reload().

So far so good, it works great! The only 'problem' is that you must explicitly call it, I mean, you must call it after each import.

What about packages?

I often write my stuff as a package, and having to explicitly reload each module could be cumbersome, not to mention having to remove those calls in production code... I'm too lazy for that.

Fortunatelly there is a workaround!

As sys.modules is just a standard dictionary it's possible manipulate the raw data by yourself. This can cause some side effects because you would be messing with python's global state, but to be honest it has saved my ass a couple of times.


import sys

def hard_reload(package_name):
    for k in sys.modules.keys():
        if k.startswith(package_name):
            del sys.modules[k]


By the way, kudos to Ángel Pavón for the tip!


Questions? Comments?

Please feel free to ping me on twitter or send me an email, I would love to hear from you!