Reloading Module

M3-R5.1 · Chapter 8: Scope and Modules · 2 min read

Reloding Modules

Why Reload a Module?

Since Python caches modules in sys.modules, if you change a module's source code after importing it, re-running import will NOT pick up the changes.

To force Python to re-read the updated file, use importlib.reload()

Syntax

from importlib import reload

reload(module_name)

Step-by-Step Example

import mymodule # First import -- loaded and cached

# (You edit mymodule.py now...)

import mymodule # Re-import -- uses cache, NO changes!

from importlib import reload

reload(mymodule) # Reload -- re-reads file, picks up changes!

Practical Example — Config File

# config.py -> DEBUG = False

import config

print(config.DEBUG) # False

# (You update config.py: DEBUG = True)

import config # Re-import does nothing

print(config.DEBUG) # Still False! (cached)

from importlib import reload

reload(config)

print(config.DEBUG) # True (reloaded from disk)

When is reload() Useful?

Interactive development in Python shell or Jupyter Notebook
When a module file changes during program execution
Testing and debugging without restarting the interpreter
Live configuration files that update dynamically

Important Points About reload()

Point	Explanation
Must import first	Module must already be imported before reloading
Partial update risk	Objects created from old version still use old code
Not recursive	Module dependencies are NOT automatically reloaded
sys.modules updated	Entry in sys.modules is refreshed after reload
Python 3 only syntax	from importlib import reload (not built-in in Python 3)

import vs reload — Key Difference

import (repeated)	reload(module)
Uses cached version from sys.modules	Re-executes the module file from disk
Does NOT pick up file changes	DOES pick up file changes
Fast (no file I/O)	Slower (reads and compiles the file again)
Default Python behavior	Requires explicit importlib.reload() call