Python: modules and packaging - why isn't __init__.py file executed before __main__.py?

问题

I have a python program that is entirely contained in a directory with the following structure:

myprog/
├── __init__.py
├── __main__.py
├── moduleone.py
└── moduletwo.py

I would like to be able to package this and distribute it so that another developer can do pip install -e /path/to/git/clone/of/myprog and can then import myprog in his own programs and do cool stuff with it.

I would also like to be able to run myprog at the command line as follows:

PROMPT> python myprog

When I do this, I expect python to execute the __main__.py module, which it does. However, this module makes references to some functions that are declared in __init__.py and which need to be available both when the program is run at the command line and when it is imported by another program. However, I'm getting the following error:

NameError: name 'function_you_referenced_from_init_file' is not defined

Do I have to import these functions into __main__.py somehow?

I tried a simple example as follows:

PROMPT> cat myprog/__init__.py
def init_myprog():
    print 'running __init__.init_myprog()'

PROMPT> cat myprog/__main__.py
import myprog
print 'hi from __main__.py'
myprog.init_myprog()

PROMPT> ls -l myprog
total 16
-rw-r--r--  1 iit    63B Aug 30 11:40 __init__.py
-rw-r--r--  1 iit    64B Aug 30 12:11 __main__.py

PROMPT> python myprog
Traceback (most recent call last):
  File "/usr/local/Cellar/python/2.7.5/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 162, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "/usr/local/Cellar/python/2.7.5/Frameworks/Python.framework/Versions/2.7/lib/python2.7/runpy.py", line 72, in _run_code
    exec code in run_globals
  File "/Users/jon/dev/myprog/__main__.py", line 1, in <module>
    import myprog
ImportError: No module named myprog

回答1:

Do I have to import these functions into __main__ somehow?

Yes. Only items in builtins are available without an import. Something like:

from myprog import func1, func2

should do the trick.

If you don't have myprog installed in the normal python path then you can work around it with something like:

import sys
import os
path = os.path.dirname(sys.modules[__name__].__file__)
path = os.path.join(path, '..')
sys.path.insert(0, path)
from myprog import function_you_referenced_from_init_file

Which, quite frankly, is horrid.

I would suggest going with MartijnPieters suggestion and put the -m on the command line, in which case __main__.py can look like:

from myprog import function_you_referenced_from_init_file

回答2:

The __init__.py is only loaded when you are import the package. You are instead treating the directory as a script, by executing the directory.

You can still treat the package as a script, instead of the directory however. To both treat the directory as a package and as the main script, by using the -m switch:

python -m myprog

回答3:

So, having looked at the other responses and not being thrilled, I tried:

from __init__ import *

from my __main__.py file.

I suppose it doesn't allow you to refer to the module by name, but for simple cases it seems to work.

来源：https://stackoverflow.com/questions/18536462/python-modules-and-packaging-why-isnt-init-py-file-executed-before-mai

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