Python Basic init , pycache & PIP

#python #programming

Why we need init?

1. Purpose of init.py

init.py file in a directory tells Python that the directory should be treated as a package.
This allows you to import modules from that directory using package syntax, e.g.:
Without init.py, Python (pre-3.3) would not recognize the folder as a package, and imports might fail.
The file can be empty, or it can contain initialization code for the package.

Starting with Python 3.3 and above (including Python 3.11), you can technically remove the init.py file from a package directory, and Python will still recognize it as a package due to "implicit namespace packages."

However, you should keep init.py:

When you add an init.py file to a package directory, it does not create a global namespace. Instead, it defines a package namespace.
All modules and submodules inside that package share the package’s namespace (e.g., tools_package.audio.utils).
This keeps your package’s contents organized and separate from the global namespace, preventing naming conflicts.

Module vs Package

Module: A single Python file (e.g., utils.py). You import it like import utils or from utils import foo.
Package: A directory containing an init.py file and (usually) multiple modules (e.g., audio/ with init.py and utils.py).

2. What is pycache?

When you run or import Python code, Python compiles .py files to bytecode for faster execution.
The compiled bytecode files are stored in the pycache directory, with names like utils.cpython-311.pyc.
cpython-311 means the file was compiled by CPython version 3.11.
These .pyc files are used by Python to speed up future imports of the module.

3. PIP (pip installs packages) (package Manager for Python):-

Using pip in a Python Virtual Environment

$ python -m venv venv/
$ source venv/bin/activate

(venv) $ pip3 --version
pip 24.2 from .../python3.12/site-packages/pip (python 3.12)

(venv) $ pip --version
pip 24.2 from .../python3.12/site-packages/pip (python 3.12)

Here you initialize a virtual environment named venv by using Python’s built-in venv module.
After running the command above, Python creates a directory named venv/ in your current working directory.
Then, you activate the virtual environment with the source command. - The parentheses (()) surrounding your venv name indicate that you successfully activated the virtual environment.
Finally, you check the version of the pip3 and pip executables inside your activated virtual environment.
Both point to the same pip module, so once your virtual environment is activated, you can use either pip or pip3.

Installing Packages With pip

 install a package
       pip install package_name
 uninstall a package
       pip uninstall package_name
 list installed packages
       pip list
 install a specific version of a package
       pip install package_name==version_number
 upgrade a package
       pip install --upgrade package_name
 show package information
       pip show package_name
 search for packages
       pip search package_name

Using Requirements Files

 requirement.text package
       pip install -r requirements.txt
 make a requirements.txt file from the packages installed
       pip freeze > requirements.txt

certifi==x.y.z
charset-normalizer==x.y.z
idna==x.y.z
requests>=x.y.z, <3.0
urllib3==x.y.z

Changing the version specifier for the requests package ensures that any version greater than or equal to 3.0 doesn’t get installed.

very important

We can create 3 files

requirements_dev.txt (For Development)
requirements_prod.txt (For Production)
requirements_lock.txt (After Development complete --> We will freeze it)

Uninstalling Packages With pip

pip show <package Name>

Name: requests
Version: 2.32.3
Summary: Python HTTP for Humans.
Location: .../python3.12/site-packages
Requires: certifi, idna, charset-normalizer, urllib3
Required-by:

Notice the last two fields, Requires and Required-by. The show command tells you that requests requires certifi, idna, charset-normalizer, and urllib3. You probably want to uninstall those too. Notice that requests isn’t required by any other package.
So it’s safe to uninstall it.