Of course! The concept of "reloading" in Python can mean a few different things, depending on whether you're in an interactive shell, running a script, or developing a library.

Let's break it down into the most common scenarios.

The Interactive Shell (e.g., python or ipython)

This is what most people mean when they ask about "Python shell reload." You're in a REPL (Read-Eval-Print Loop), you've imported a module, changed its source code, and you want those changes to take effect without restarting the shell.

The Problem: import Doesn't Reload

If you just run import my_module again, Python won't reload it. It sees that my_module is already in its cache (sys.modules) and simply reuses the existing, already-loaded version.

# In your interactive shell
>>> import my_module
>>> my_module.my_variable
10
# Now, you edit my_module.py and change my_variable to 20
# Go back to the shell and try to re-import
>>> import my_module
>>> my_module.my_variable
# Still 10! The change is not reflected.
10

The Solution: importlib.reload()

The standard and correct way to do this is with the importlib module.

Step 1: Import importlib

>>> import importlib

Step 2: Reload your module

>>> importlib.reload(my_module)
<module 'my_module' from '/path/to/my_module.py'>

Step 3: Check for the changes

>>> my_module.my_variable
20 # Success! The change is now reflected.

Important Note: You must use the name of the module object you imported, not the string name.

# CORRECT (reloads the already imported module object)
>>> importlib.reload(my_module)
# INCORRECT (tries to load a new module named 'my_module')
>>> importlib.reload('my_module')
TypeError: reload() argument must be a module

Pro Tip: The IPython Magic %autoreload

If you use IPython or Jupyter Notebooks, there's a much more convenient magic command. This is the recommended workflow for interactive development.

1. Load the extension:

   %load_ext autoreload

2. Set the mode:

   • %autoreload 1: Reload all modules imported with %aimport (see below).
   • %autoreload 2: Reload all modules (except those explicitly excluded) before every execution. This is the most common and powerful mode.

   %autoreload 2

Now, every time you run a cell, IPython will automatically reload any modules you've imported if their source files have changed.

# In an IPython/Jupyter cell with %autoreload 2 active
import my_module
print(my_module.my_variable) # Prints 10
# Edit my_module.py, change my_variable to 20
# Run the cell again
import my_module
print(my_module.my_variable) # Automatically prints 20!

Running a Python Script from the Command Line

If you're running a script like python my_app.py and you change a file it imports, you need to stop the script and run it again.

The Modern Solution: watchdog

Manually stopping and restarting is tedious. A common pattern is to use a file watcher that automatically restarts your application when a file changes. The most popular tool for this is watchdog.

1. Install watchdog:

   pip install watchdog

2. Create a simple runner script (e.g., run.py):

   import time
   import subprocess
   import sys
   from watchdog.observers import Observer
   from watchdog.events import FileSystemEventHandler
   class RestartHandler(FileSystemEventHandler):
       def on_modified(self, event):
           if event.src_path.endswith('.py'):
               print("\n>> Python file modified. Restarting app...")
               # Kill the old process
               subprocess.call(["pkill", "-f", "python run.py"])
               # Restart the new process
               subprocess.Popen([sys.executable, "my_app.py"])
   if __name__ == "__main__":
       event_handler = RestartHandler()
       observer = Observer()
       observer.schedule(event_handler, path='.', recursive=False)
       observer.start()
       try:
           # Start the initial application
           process = subprocess.Popen([sys.executable, "my_app.py"])
           process.wait()
       except KeyboardInterrupt:
           observer.stop()
       observer.join()

Now, when you run python run.py, it will launch my_app.py. If you save any .py file in the current directory, run.py will automatically restart my_app.py.

Reloading a Module Within a Running Application (Advanced)

Sometimes you want to reload a module that's already part of a long-running process (like a web server or a daemon). This is highly discouraged for production code because it's complex and can lead to unpredictable state, memory leaks, or crashes.

However, it can be useful in development. The importlib.reload() function is the tool for this, but you must be aware of its pitfalls.

How reload() Works:

1. The module's existing code object is re-executed.
2. The module's namespace (its dictionary of globals) is updated with any new or changed names.
3. Existing references to objects in the module (like classes or functions) are NOT updated. They will still point to the old objects.

Example of the Pitfall:

Let's say you have my_module.py:

# my_module.py
class MyClass:
    def greet(self):
        return "Hello from old version"

And your main app app.py:

# app.py
import my_module
# Get a reference to the class
my_instance = my_module.MyClass()
print(my_instance.greet()) # "Hello from old version"
# --- NOW, you edit my_module.py ---
# my_module.py (new version)
class MyClass:
    def greet(self):
        return "Hello from NEW version!"
# --- Back in the running app.py ---
# Reload the module
import importlib
importlib.reload(my_module)
# Create a new instance
new_instance = my_module.MyClass()
print(new_instance.greet()) # "Hello from NEW version!"
# BUT the old instance is still the old class!
print(my_instance.greet()) # Still "Hello from old version"!

Because my_instance was created before the reload, it still points to the old MyClass definition.

Summary: Which Method to Use?