Q. Module

Python has a way to put definitions in a file and use them in a script or in an interactive instance of the interpreter. Such a file is called a module; definitions from a module can be imported into other modules or into the main module.

A module is a file containing Python definitions and statements. Within a module, the module’s name (as a string) is available as the value of the global variable __name__

Each module has its own private symbol table, which is used as the global symbol table by all functions defined in the module.

Ex. we had a fibo.py. There are two functions fib(n) and fib2(n)

we can use it like

import fibo
fibo.fib(1000)
fibo.fib2(100)
fib = fibo.fib
fib(500)

There is a variant of the import statement that imports names from a module directly into the importing module’s symbol table

from fibo import fib, fib2 
fib(500)

Q. Main module

Python modules are objects and have several useful attributes. All modules have a built-in attribute __name__. you can also run the module directly as a standalone program, in which case __name__ will be a special default value, __main__

if __name__ == "__main__": 
    # main program here

Q. Package

使用 Python 時，你可以在開設的目錄中放個 __init__.py 檔案，這樣 Python 就會將這個目錄視為一個套件，而目錄名稱就是套件名稱。

使用 import pack.moduA 陳述時，Python 會尋找 pack目錄，看看裏頭是否有 __init__.py 檔案，然後看看目錄中是否有個 moduA.py 檔案。__init__.py 檔案空白也無所謂，實際上當中也可以寫些程式碼，用來執行這個套件中都會需要的初始工作，不過慣例上，除非你有真正不得已的理由，請保持 __init__.py 檔案空白。