Python模块和Python package有什么区别？

Question

What's the difference between a Python module and a Python package?

See also: What's the difference between "package" and "module" (for other languages)

Answer 1

Any Python file is a module , its name being the file's base name without the .py extension. A package is a collection of Python modules: while a module is a single Python file, a package is a directory of Python modules containing an additional __init__.py file, to distinguish a package from a directory that just happens to contain a bunch of Python scripts. Packages can be nested to any depth, provided that the corresponding directories contain their own __init__.py file.

The distinction between module and package seems to hold just at the file system level. When you import a module or a package, the corresponding object created by Python is always of type module . Note, however, when you import a package, only variables/functions/classes in the __init__.py file of that package are directly visible, not sub-packages or modules. As an example, consider the xml package in the Python standard library: its xml directory contains an __init__.py file and four sub-directories; the sub-directory etree contains an __init__.py file and, among others, an ElementTree.py file. See what happens when you try to interactively import package/modules:

>>> import xml
>>> type(xml)
<type 'module'>
>>> xml.etree.ElementTree
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'etree'
>>> import xml.etree
>>> type(xml.etree)
<type 'module'>
>>> xml.etree.ElementTree
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'ElementTree'
>>> import xml.etree.ElementTree
>>> type(xml.etree.ElementTree)
<type 'module'>
>>> xml.etree.ElementTree.parse
<function parse at 0x00B135B0>

In Python there also are built-in modules, such as sys , that are written in C, but I don't think you meant to consider those in your question.

Answer 2

A module is a single file (or files) that are imported under one import and used. eg

import my_module

A package is a collection of modules in directories that give a package hierarchy.

from my_package.timing.danger.internets import function_of_love

Documentation for modules

Introduction to packages

Answer 3

First, keep in mind that, in its precise definition, a module is an object in the memory of a Python interpreter, often created by reading one or more files from disk. While we may informally call a disk file such as a/b/c.py a "module," it doesn't actually become one until it's combined with information from several other sources (such as sys.path ) to create the module object.

(Note, for example, that two modules with different names can be loaded from the same file, depending on sys.path and other settings. This is exactly what happens with python -m my.module followed by an import my.module in the interpreter; there will be two module objects, __main__ and my.module , both created from the same file on disk, my/module.py .)

A package is a module that may have submodules (including subpackages). Not all modules can do this. As an example, create a small module hierarchy:

$ mkdir -p a/b
$ touch a/b/c.py

Ensure that there are no other files under a . Start a Python 3.4 or later interpreter (eg, with python3 -i ) and examine the results of the following statements:

import a
a                ⇒ <module 'a' (namespace)>
a.b              ⇒ AttributeError: module 'a' has no attribute 'b'
import a.b.c
a.b              ⇒ <module 'a.b' (namespace)>
a.b.c            ⇒ <module 'a.b.c' from '/home/cjs/a/b/c.py'>

Modules a and ab are packages (in fact, a certain kind of package called a "namespace package," though we wont' worry about that here). However, module abc is not a package. We can demonstrate this by adding another file, a/b.py to the directory structure above and starting a fresh interpreter:

import a.b.c
⇒ ImportError: No module named 'a.b.c'; 'a.b' is not a package
import a.b
a                ⇒ <module 'a' (namespace)>
a.__path__       ⇒ _NamespacePath(['/.../a'])
a.b              ⇒ <module 'a.b' from '/home/cjs/tmp/a/b.py'>
a.b.__path__     ⇒ AttributeError: 'module' object has no attribute '__path__'

Python ensures that all parent modules are loaded before a child module is loaded. Above it finds that a/ is a directory, and so creates a namespace package a , and that a/b.py is a Python source file which it loads and uses to create a (non-package) module ab . At this point you cannot have a module abc because ab is not a package, and thus cannot have submodules.

You can also see here that the package module a has a __path__ attribute (packages must have this) but the non-package module ab does not.

Answer 4

From the Python glossary :

It's important to keep in mind that all packages are modules, but not all modules are packages. Or put another way, packages are just a special kind of module. Specifically, any module that contains a __path__ attribute is considered a package.

Python files with a dash in the name, like my-file.py , cannot be imported with a simple import statement. Code-wise, import my-file is the same as import my - file which will raise an exception. Such files are better characterized as scripts whereas importable files are modules .

Answer 5

A late answer, yet another definition:

A package is represented by an imported top-entity which could either be a self-contained module, or the __init__.py special module as the top-entity from a set of modules within a sub directory structure.

So physically a package is a distribution unit, which provides one or more modules.

Answer 6

Module : A module is a simple Python file with a ( .py ) extension that contains collections of functions and global variables. It is an executable file, and the notion of Package in Python is used to arrange all of the modules.

For an Example : Save the code in a file called demo ( module.py ).

def myModule1(name):
    print("My Module name is: "+ name)

Import the demo module module and use the myModule1 function within it.

import demo_module
  
demo_module.myModule1("Math")

Solution:

My Module name is: Math

Package: A package is a basic directory that contains a collection of modules. This directory contains Python modules as well as a ( __init.py__ ) file that the interpreter uses to recognize it as a Package. The package is nothing more than a namespace. Within the package, there are sub-packages.

For an Example:

Student (Package)

| __init__.py (Constructor)

| details.py (Module)

| marks.py (Module)

| collegeDetails.py (Module)

| demo_module.py (Module)

A package is a set of modules organized into directories to form a package directory.

from Student import details, collegeDetails, demo_module

Answer 7

I read the different answers given to this question. The issue is fully covered. But it seems to me that making an extra point may not be a bad idea. If we examine the value of __package__ for different modules, we reach the following result. All of them are module types but for some of them the package is not defined. Check __package__ for " random " and " math ".

import cv2
import math
import random
import tkinter as tk

print('cv2:',type(cv2))             # <class 'module'>
print('cv2:',cv2)                   # <module 'cv2.cv2' from 'PATH'>
print('cv2:',cv2.__package__)       # cv2

print('random:',type(random))       # <class 'module'>
print('random:',random)             # <module 'random' from 'PATH'>
print('random:',random.__package__) # [EMPTY]

print('tk:',type(tk))               # <class 'module'>
print('tk:',tk)                     # <module 'tkinter' from 'PATH'>
print('tk:',tk.__package__)         # tkinter

print('math:',type(math))           # <class 'module'>
print('math:',math)                 # <module 'math' (built-in)>
print('math:',math.__package__)     # [EMPTY]

So if we define a folder as follows:

This is how we can see the __package__ output:

import myfolder
import myfolder.script1 as s1
import myfolder.script2 as s2
import myfolder.mySubfolder.script3 as s3

print(type(s1)) # <class 'module'>
print(type(s2)) # <class 'module'>
print(type(s3)) # <class 'module'>

print(s1.__package__) # myfolder
print(s2.__package__) # myfolder
print(s3.__package__) # myfolder.mySubfolder

print(myfolder)                     # <module 'myfolder' (namespace)>
print(myfolder.mySubfolder)         # <module 'myfolder.mySubfolder' (namespace)>
print(myfolder.mySubfolder.script3) # <module 'myfolder.mySubfolder.script3' from 'PATH'>

print(myfolder.__package__)                     # myfolder        
print(myfolder.mySubfolder.__package__)         # myfolder.mySubfolder
print(myfolder.mySubfolder.script3.__package__) # myfolder.mySubfolder

Answer 8

The other answers here may still be a bit vague, so I'm posting a hopefully clearer answer. It's important to note that the title of the question is also a bit misleading in the first place, and a better title in my opinion would be: " What is special about package modules compared to regular modules? " .

TL;DR - Short Answer:

Packages are modules too, they are however, a special type of them. Special in the sense that 1. they are "directories" and 2. they may contain special files such as __init__.py and __main__.py .

To Better Understand - Longer Answer:

The point is, packages are a special type of modules , so we need to understand modules in general first, and then what's special about the package modules will make sense too. (Notice: I'll sometimes refer to "package modules" in this answer as just "packages", and vice versa)

So let's talk about modules in general first, as it would be less vague / easier to understand. There are basically two things that we do with modules, we either import them in other modules, or execute them directly by Python.

Importing a module has a single obvious goal, accessing what that module has inside.

Executing a module however, usually pursues one of these two goals:

1. That module is a main module and executing it will start our program (or one of its subprograms).
2. We want to try the functionalities of that module in isolation, ie, without having to import it first.

Let's make more sense of all these through some examples:

Importing modules:

# bar.py

def talk():
    print("bar")

# foo.py

import bar # <-- importing module "bar"

bar.talk() # <-- prints "bar"

Executing Modules

Goal 1, executing a module as a main module:

Let's assume that the foo.py module in the example above, is a main module that starts our program. We can run it by typing this command in the terminal: python3 foo.py # <-- executing a main module and then it will start our program.

Goal 2, trying functionalities of a module in isolation:

Let's assume that we want to try the function talk in the bar.py module in the example above, without running our whole program, ie, without calling the module foo.py . For that, we'll have to slightly change the bar.py :

# bar.py

def talk():
    print("bar")

if __name__ == '__main__':
    talk()

Now run this command in the terminal: python3 bar.py # <-- trying functionalities of a module in isolation and then it will print bar .

Now that we know what we can do with modules in general, let's return to the main question:

What is special about package modules compared to regular modules?

1. Regular modules in Python are just "files", package modules are however, "directories".

2. Regular modules can be "imported" and can be "executed" (as shown in the examples above), package modules ALSO can be "imported" and can be "executed", HOWEVER, you may rightly complain: " but we can't directly write code in directories! Code is written in files only!" , and that's indeed a very good complaint, as it leads us to the second special thing about package modules. The code for a package module is written in files inside its directory , and the names of these files are also reserved by Python. If you want to "import" a package module, you'll have to put its code in an __init__.py file in its directory, and if you want to "execute" a package module, you'll have to put the execution code of it in a __main__.py file in its directory.

And here's the final example for the explanation above:

# hierarchy of files and folders:
.
├── bar_pack/
│   ├── __init__.py
│   ├── __main__.py
│   foo.py

# bar_pack/__init__.py

def talk():
    print("bar")

# bar_pack/__main__.py

import __init__

__init__.talk()

# foo.py

import bar_pack # <-- importing package module "bar_pack"

bar_pack.talk() # <-- prints "bar"

# Run this command in the terminal:
python3 bar_pack # <-- executing the package module "bar_pack", prints "bar"

Answer 9

I know, it's too late, but a simple answer which would be sufficient for some is:

a module is a file,

a package is a folder.