How to check if python module exists and can be imported

I am using debug toolbar with django and would like to add it to project if two conditions are true:

• settings.DEBUG is True
• module itself exists

It's not hard to do the first one

# adding django debug toolbar
if DEBUG:
    MIDDLEWARE_CLASSES += 'debug_toolbar.middleware.DebugToolbarMiddleware',
    INSTALLED_APPS += 'debug_toolbar',

But how do I check if module exists?

I have found this solution:

try:
    import debug_toolbar
except ImportError:
    pass

But since import happens somewhere else in django, I need if/else logic to check if module exists, so I can check it in settings.py

def module_exists(module_name):
    # ??????

# adding django debug toolbar
if DEBUG and module_exists('debug_toolbar'):
    MIDDLEWARE_CLASSES += 'debug_toolbar.middleware.DebugToolbarMiddleware',
    INSTALLED_APPS += 'debug_toolbar',

Is there a way to do it?