Does Python Cache Imports?
As an avid Python developer, I have come across this question multiple times. So, let's answer it!
What is Importing in Python?
Before jumping into whether Python caches imports or not, let's first understand what importing means in Python. When we write a Python script, we often require help from other modules or packages to carry out specific tasks. These external modules are imported into our script using the "import" statement.
import module_name
This statement allows us to use the functions and classes defined in the imported module.
How does Python Import Modules?
When we import a module for the first time, Python searches for the module in the sys.path. If found, it compiles the module into byte code and stores it in the __pycache__ directory in a file named module_name.version.pyc.
The file name contains the version number of the Python interpreter and is used to ensure that the correct bytecode is loaded when running the script.
Does Python Cache Imports?
Yes, Python does cache imports. When a module is imported for the first time, it's compiled into bytecode and stored in the __pycache__ directory. The next time the same module is imported, Python checks if the bytecode has already been generated and if it exists, directly loads it instead of recompiling the module.
This caching mechanism helps reduce the startup time of Python scripts as importing modules can be time-consuming. Additionally, it also ensures that our code uses the same version of the module throughout its runtime, even if the module is updated.
How to Disable Import Caching?
In some cases, we may want to disable import caching. For example, if we are testing a module and making changes to it, we would want Python to recompile the module every time it's imported.
To disable import caching, we can use the -B flag when running the Python script or set the PYTHONDONTWRITEBYTECODE environment variable to 1.
Conclusion
In conclusion, Python does cache imports to improve the startup time of scripts and ensure that the same version of the module is used throughout the runtime. However, we can disable import caching using the -B flag or by setting the PYTHONDONTWRITEBYTECODE environment variable to 1.