Running without Python source files in Python 3.4

Question

I'm trying to run a Python application without keeping the .py source files around, and only relying on the .pyc compiled files. However, I am getting import errors when I remove the .py source files. This functionality is working in Python 2.7, but not in 3.4 (with the new __pycache__ structure).

Here's a sample directory structure:

package/
  __init__.py
  module.py

Python 2.7

First let's see what happens when I use Python 2.7 (this is the desired behavior)

$ python2 -c "from package import module"
$ find package -name "*.py" -delete
$ python2 -c "from package import module"

It's all good and no errors are thrown. The directory structure after doing this would look like this, with the .pyc files along side the original .py files:

package/
  __init__.pyc
  module.pyc

Python 3.4

Now, let's do the same thing with Python 3.4, starting with our original directory structure again

$ python3 -c "from package import module"
$ find package -name "*.py" -delete
$ python3 -c "from package import module"
 Traceback (most recent call last):
   File "<string>", line 1, in <module>
 ImportError: cannot import name 'module'

Uh oh, it can't import the module. Interestingly, I could still safely run python3 -c "import package" at this point, but it can't grab any modules out of there. At this point, the directory structure looks a little different than it did in 2.7, specifically like this:

package/
  __pycache__/
      __init__.cpython-34.pyc
      module.cpython-34.pyc

So the question is this: why can't Python 3.4 import/execute properly given only .pyc files? Is this desired behavior, meaning that the source has to be kept around in all situations? Or am I missing something stupid?

Answer 1

No enough reputation to add comment to BrenBarn's answer. So here is some complement.

According to the compileall doc:

-b

Write the byte-code files to their legacy locations and names, which may overwrite byte-code files created by another version of Python. The default is to write files to their PEP 3147 locations and names, which allows byte- code files from multiple versions of Python to coexist.

So you could run python -m compileall -b . to compile all the code files in this directory recursively.