python bag module references and carded

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This link: https://blog.csdn.net/DD_PP_JJ/article/details/102766918

Introduction: In view some of the code works, always will find something like:
from .util import utils
from . import datasets
Such statements referencing, which made me more confused, so take advantage of this opportunity to spend some time, a good tidy-related knowledge

1. python package mechanism

- 包
- 模块
- 框架： 如何组织包和模块

python provides the concept of packages, there is a hierarchical file directory structure for managing a plurality of modules source files.

Package is the folder, this has __init__.py file folder, and the folder may include other modules
A plurality of modules associated with a package, in order to maintain and use, at the same time can be limited to avoid conflicts namespace.
Importing a package in time, we will first call this package __init__.py file

Seated problems: from small to large

Statement
Def function
Class class
Module module, physically one file python
Package bag, physically a folder, the package may contain modules and packages

Packages and action module:

Write good wheels, tools, for use other modules

Effectively break down the program, to facilitate the management and maintenance of the code

Named prevent the problem repeat the same module (module1.name, module2.name)

– from bilibili https://www.bilibili.com/video/av65157512?p=2

Package information basic module and

Packages and module name
- __name__
- __package__
Storage location
- __file__
View the contents of the package and modules
- dir (os)
- __dict__

Import package / module by:

General Import:
- import M
  - Directly into the same directory import M
  - Different level directory using dot syntax import pkg1.pkg2.M
- import M1, M2
- import M as m
- from A import B as b, C as c
  - A range is greater than B, C
    - Range: Package> Module> Resources
  - B, C this part as simple as possible
    - Right: from A.A1 import aa
    - Error: from A import A1.aa
- from module import *
  - The module will then go to the corresponding python files to find __all__the contents of the corresponding variable
- from 包 import *
  - Then the package will go to the corresponding __init__.pyfile to find the __all__corresponding variable content
note:
- In use, the subject should be introduced into the module, rather than the package
- If a package is introduced, not import any default module
- solution:
  - In this package __init__.pyimport all the modules required
  - In the package from / import folder modules / sub-packet form introduced
    - from p1 import Tool1 as t1, Tool2 as t2
    - from p1.sub_p import sub_xx
  - from module import name form of import resources
    - from other import num

Encountered no module named xxx

  import sys
  sys.path.append('rc:\Desktop\xxx_dir')
  import xxx
  # 比较强硬的解决方法

Module search order:
- Built> Custom> sys.path

2. python module relative references

Many times you'll meet the following error:

ValueError: attempted relative import beyond top-level package

This is usually due to the use of relative references and emerging issues.

We need to be clear:

Relative references are not relative to the file structure! !
With respect to the relative reference is__name__

for example:

- rootdir
  - subdir1
    - __init__.py
  	- subfile1.py
  - subdir2 
    - __init__.py
    - subfile2.py
- test.py

test.py call content subfile1.py of:

def print_mod1():
    print('__name__: {}'.format(__name__))
    print('__package__: {}'.format(__package__))
    print('Import Successfully!')

The output is:

__name__: subdir1.subfile1
__package__: subfile1
Import Successfully!

So this is the relative position with respect to __name__variables, such as:

A point: .on behalf of the current is subdir1

Point two: ..does not exist, the error will beyond top-level package, where top-level package is also very easy to understand, and that is the current subdir1.

You can view more content: https://www.cnblogs.com/jay54520/p/8438228.html

3. Examples

Directory structure is as follows:

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model folder:

__init__.py · Document reads as follows:

print('-'*5,"init for model folder",'-'*5)

models.pyDocument reads as follows:

def mm():
    print("this is rootpkg/model/models/model")
    print('__name__: {}'.format(__name__))
    print('__package__: {}'.format(__package__))

src folder:

__init__.py · Document reads as follows:

print('-'*5,"init for src folder",'-'*5)

source.pyDocument reads as follows:

def ss():
    print("this is rootpkg/src/source/src")
    print('__name__: {}'.format(__name__))
    print('__package__: {}'.format(__package__))

RootPkg folder:

__init__.py · Document reads as follows:

print('-'*5,"init for rootpkg folder",'-'*5)

main.pyDocument reads as follows:

from model import models
from src import source
from 模块/文件夹 import 具体某个python文件名

source.ss()
models.mm()

Results are as follows:

----- init for model folder -----  
----- init for src folder ----- 
# 这两个是在import模块的时候执行的__init__.py文件
this is rootpkg/src/source/src
__name__: src.source
__package__: src
this is rootpkg/model/models/model
__name__: model.models
__package__: model

After the run there will be complete __pycache__folders

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Run successfully, but the best practices Tommy-Yu did not go straight through that part, you can look at the first reference of the blog, if anyone can run through, welcome to contact me. (Ps: personally I feel this blog is not said very clearly, the actual operation does go wrong)