imp.load_source from within package

Question

For some Python project, I defined the default configuration in a config module. Customization is allowed by sourcing a rc file into it using

config = imp.load_source('config', 'some_rc_file')

The rc file might redefine only a subset of the configuration variables, or even not at all, and I expect that variables which are not redefined would still exist as attributes of the config module, with their default value. If load_source is called from __main__, everything goes well. However, if it is used within a package, the only variables 'left' in the module are those of the rc file.

There's a MWE here. direct.py works as expected, but not indirect.py

.
|-- run.sh                           # runs python {,in}direct.py
|-- altconfig.py                     # the rc file, redefines (only) BAR
|-- config.py -> testimp/config.py   # symlink to use by direct.py
|-- direct.py                        # calls load_source directly
|-- indirect.py                      # calls load_source via uses_config.py
`-- testimp
    |-- __init__.py
    |-- config.py                    # default config, defines FOO and BAR
    `-- uses_config.py

What import logic am I missing?

Ned Batchelder · Accepted Answer · 2014-12-30 12:54:47Z

2

If you add print(config) to your test code, you'll see that the module imported by import config is named config, but the module imported by from . import config in testimp is called testimp.config. The first argument to load_source is the name of the module to reuse. Since you are looking for config, your existing import isn't found, and you get a new module object.

The simplest solution is to not hard code the name of the module. Change your imp lines to this, and it will work everywhere:

config = imp.load_source(config.__name__, 'altconfig.py')

answered Dec 30, 2014 at 12:54

Ned Batchelder

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