package and module

我們先從package開始吧。根據python文件的說法，package是一種帶有__path__屬性的module

A Python module which can contain submodules or recursively, subpackages.
Technically, a package is a Python module with an __path__ attribute.

根據這段描述帶出了兩個問題

1. what is module
2. what is __path__

先來看第一個問題，module是甚麼概念呢?

An object that serves as an organizational unit of Python code.
Modules have a namespace containing arbitrary Python objects.
Modules are loaded into Python by the process of importing.

namespace代表甚麼呢?

• The place where a variable is stored
• implemented as dictionaries
• local, global and built-in namespaces as well as nested namespaces in objects (in methods)

再來看第二個問題

A package’s __path__ attribute is used during imports of its subpackages.
Within the import machinery, it functions much the same as sys.path, i.e. providing a list of locations to search for modules during import.

1. 看起來module的本質上是一個物件。
2. __path__的目的是存放import過程中會使用到的資料，與sys.path的功能性上類似

結論是一個包含__path__屬性的物件即為package

有兩種類型的package

1. regular packages
   • traditional packages as they existed in Python 3.2 and earlier
   • typically implemented as a directory containing an __init__.py file.
   • When a regular package is imported, this __init__.py file is implicitly executed
2. namespace packages

__init__.py in requests

因為requests目錄帶有__init__.py，所以可以將requests看成是一個regular package，當requests被其他module import時，預設會執行__init__.py

1. 檢查urllib3和chardet相容性
   • urllib3 >= 1.21, <= 1.25
   • chardet >= 3.0.2, < 3.1.0
2. 建議cryptography >= 1.3.4
3. 從__version__載入相關資訊，例如title, description, version, author...
4. 載入requests需要用到的物件或函式，使用了relative import

from . import utils
from . import packages
from .models import Request, Response, PreparedRequest
from .api import request, get, head, post, patch, put, delete, options
from .sessions import session, Session
from .status_codes import codes
from .exceptions import (
    RequestException, Timeout, URLRequired,
    TooManyRedirects, HTTPError, ConnectionError,
    FileModeWarning, ConnectTimeout, ReadTimeout
)

參考

• glossary-package
• glossary-module
• glossary-namespace
• module.__path__
• the-import-system
• package-relative-imports