how to reload a Class in python shell?

On Python 3 only, import the reload function:

>>> from importlib import reload

On both Python 2.x, and 3.x, you can then simply call reload on the module:

>>> import MyPak
>>> reload(MyPak)
>>> from MyPak import MyMod

However, instances of the old class will not be updated (there's simply no code that describes the update mechanism).

I finally found the answer:

import MyPak
from MyPak import MyMod

after editing MyPak/MyMod.py file, to reload the class MyMod in the file MyMod.py, one needs to

import sys
del sys.modules['MyPak.MyMod'] 
reload(MyPak)
from MyPak import MyMod

Caveats:

1. Executing del MyPak or del MyMod or del MyPak.MyMod does not solve the problem since it simply removes the name binding. Python only searches sys.modules to see whether the modules had already been imported. Check out the discussion in the post module name in sys.modules and globals().

2. When reloading MyPak, python tries to execute the line from MyMod import MyMod in MyPak/__init__.py. However, it finds MyPak.MyMod in sys.modules, thus it will NOT reload MyMod although MyPak/MyMod.py has been updated. And you will find that no new MyPak/MyMod.pyc is generated.

There are thee ways to solve this:

1. Use import MyPak.MyMod instead of from MyPak import MyMod

Then you can write:

from importlib import reload  # If on Python 3
import MyPak.MyMod
reload(MyPak.MyMod)

and it works.

2. Use IPython.lib.deepreload

from MyPak import MyMod
from IPython.lib.deepreload import reload
reload(MyPak)  # This should also reload all submodules

3. Use autoreload magic

%load_ext autoreload
%autoreload 2
import MyPak.MyMod  # All changes to MyPak.MyMod will be loaded automatically

You can use a magic function:

%load_ext autoreload
%autoreload 2
from MyPak import MyMod

It also works for function imports:

%load_ext autoreload
%autoreload 2
from anypythonfile import my_function

This magic function works in Python 2.x (I've tested on 2.7+) and Python 3.x (I've tested on 3.7).

I have one myfile.py file which contains one class MyClass

To import just do:

from myfile import MyClass
mc = MyClass()

To reload:

import sys
del sys.modules['myfile']
from myfile import MyClass
modifiedmc = MyClass()

This is very useful while building modules. one can put these inside a function and just call the function

def myreload():
   import sys
   del sys.modules['myfile']
   from myfile import MyClass
   modifiedmc = MyClass()
   global mc
   mc = modifiedmc