重新加载模块，给出NameError：名称’reload’未定义

I’m trying to reload a module I have already imported in Python 3. I know that you only need to import once and executing the import command again won’t do anything.

Executing reload(foo) is giving this error:

Traceback (most recent call last):
    File "(stdin)", line 1, in (module)
    ...
NameError: name 'reload' is not defined

What does the error mean?

reload is a builtin in Python 2, but not in Python 3, so the error you’re seeing is expected.

If you truly must reload a module in Python 3, you should use either:

• importlib.reload for Python 3.4 and above
• imp.reload for Python 3.0 to 3.3 (deprecated since Python 3.4 in favour of importlib)

For >= Python3.4:

import importlib
importlib.reload(module)

For <= Python3.3:

import imp
imp.reload(module)

For Python2.x:

Use the in-built reload() function.

reload(module)

import imp
imp.reload(script4)

To expand on the previously written answers, if you want a single solution which will work across Python versions 2 and 3, you can use the following:

try:
    reload  # Python 2.7
except NameError:
    try:
        from importlib import reload  # Python 3.4+
    except ImportError:
        from imp import reload  # Python 3.0 - 3.3

I recommend using the following snippet as it works in all python versions (requires six):

from six.moves import reload_module
reload_module(module)

For python2 and python3 compatibility, you can use:

# Python 2 and 3
from imp import reload
reload(mymodule)

If you don’t want to use external libs, then one solution is to recreate the reload method from python 2 for python 3 as below. Use this in the top of the module (assumes python 3.4+).

import sys
if(sys.version_info.major>=3):
    def reload(MODULE):        
        import importlib
        importlib.reload(MODULE)

BTW reload is very much required if you use python files as config files and want to avoid restarts of the application…..