Python---Referencing functions in other PY files

There are two ways to implement it, the first one has 2 small methods, the 2nd one is more formal add __init.py__

Description
Create a new file in the directory where you want to reference the file and the PY directory you want to execute: __init.py__, which you can reference by relative path
Method 1
The directory is as follows:

py_test/
├──a
│   ├──a.py
│   └──__init__.py
├──b
│   ├──b.py
│   └──__init __.py
└──__init__.py

a.py content:

# Coding:utf8
def A ():
    print ("I am a")

b.py content:

# Coding:utf8 from
. A import a
a.a ()

Other file is empty
and py_test the same directory, execute the command:

Python-m py_test.b.b

You can call a function in a.py

Method 2
The disadvantage of Method 1 is that you can only execute commands under that path, and if you do not want to use Method 1, you can only encapsulate the code in b.py into a function, create a new c.py under the Py_test folder, and invoke the functions encapsulated in b.py by c.py, which is a more formal approach.
The directory is as follows:

Py_test
├──a
│   ├──a.py
│   └──__init__.py
├──b   │ ├──b.py │ └──__init__. PY
└──c.py

a.py content:

# Coding:utf8

def A ():
    print ("I am a")

b.py content:

# Coding:utf8 from

a.a import a

def b ():
    print ("I am b!")
    A ()

c.py content:

# Coding:utf8 from

b.b import b

B ()

Other files are empty, for example, to execute commands under Py_test:

Python c.py

The sys add path can be performed normally

Description
Add the directory path of the file you want to use to the system path to refer to the
The main forms are as follows:

Import sys
sys.path.append (path)

Use the above form to be aware of using absolute paths, and to note the path differences caused by the operating system