问题

I want to run a Pythonic project using Python compilation (.pyc or __pycache__). In order to do that in Python2, I haven't any problem.

Here is a simplified example in a Python2 project:

Project tree:

test2
├── main.py
└── subfolder
    ├── __init__.py
    └── sub.py

Compile:
```
python -m compileall test2
```

Project tree after the compile:

test2
├── main.py
├── main.pyc
└── subfolder
    ├── __init__.py
    ├── __init__.pyc
    ├── sub.py
    └── sub.pyc

As you can see, several .pyc manually generated. Now I can run this project using main.pyc as fine, which has a relation with the sub.py:
```
python main.pyc
```
Out:
```
Hi
Bye
```

main.py content:

from subfolder import sub

print('Bye')

sub.py content:
```
print('Hi')
```

Now I want to retry this behavior in a Python3 project.

Here is a simplified asyncio (available in Python3) project:

Project tree:

test3
├── main.py
└── subfolder
    ├── __init__.py
    └── sub.py

Compile:
```
python3 -m compileall test3
```

Project tree after the compile:

test3
├── main.py
├── __pycache__
│   └── main.cpython-36.pyc
└── subfolder
    ├── __init__.py
    ├── __pycache__
    │   ├── __init__.cpython-36.pyc
    │   └── sub.cpython-36.pyc
    └── sub.py

As you can see, __pycache__ folders manually generated. But I cannot run this project using main.cpython-36.pyc which has a relation with subfolder:
```
cd test3/__pycache__
python3 main.cpython-36.pyc
```
Out (I expected that produced the Hi Bye message):
```
Traceback (most recent call last):
  File "test3/main.py", line 2, in <module>
ModuleNotFoundError: No module named 'subfolder'
```

main.py content:

import asyncio
from subfolder import sub

async def myCoroutine():
    print("Bye")

def main():
    loop = asyncio.get_event_loop()
    loop.run_until_complete(myCoroutine())
    loop.close()

main()

sub.py content:
```
print('Hi')
```

Question:

How can I run this project (above Python3 project) using __pycache__ folder?

How can I run a Python3 project with the relation between subfolders using python compilation?

[NOTE]:

I cannot use the python compileall (Python2 compile) in the above Python3 project due to the asyncio method.
My Python(s) version is Python2.7 and Python3.6

回答1:

You can enforce the same layout of pyc-files in the folders as in Python2 by using:

python3 -m compileall -b test3

The option -b triggers the output of pyc-files to their legacy-locations (i.e. the same as in Python2).

After that you can once again use the compiled cache via:

python3 main.pyc

The way the loading of modules works since PEP-3147, it is impossible to use pyc-files from __pycache__ folder in the way you intend: If there is no *.py-file, the content of the __pycache__ is never looked-up. Here is the most important part of the workflow:

   import foo
     |
     |
     -- >  [foo.py exists?]  --- NO ----> [foo.pyc exists?]  -- NO --> [ImportError] 
            |                                     |
            |                                    YES
           YES                                    |--> [load foo.pyc]
            |
            |-> [look up in __pycache__]

That means, files from __pycache__ are only looked up, when a corresponding *.py-file can be found.

来源：https://stackoverflow.com/questions/53918318/how-to-run-a-python-project-using-pycache-folder

标签

python