How Does Python Find a Module File If the Import Statement Only Contains the Filename

How does python find a module file if the import statement only contains the filename?

http://docs.python.org/3/tutorial/modules.html#the-module-search-path

6.1.2. The Module Search Path

When a module named spam is imported, the interpreter first searches for a built-in module with that name. If not found, it then searches for a file named spam.py in a list of directories given by the variable sys.path. sys.path is initialized from these locations:

• The directory containing the input script (or the current directory when no file is specified).
• PYTHONPATH (a list of directory names, with the same syntax as the shell variable PATH).
• The installation-dependent default.

Note: On file systems which support symlinks, the directory containing the input script is calculated after the symlink is followed. In other words the directory containing the symlink is not added to the module search path.

After initialization, Python programs can modify sys.path. The directory containing the script being run is placed at the beginning of the search path, ahead of the standard library path. This means that scripts in that directory will be loaded instead of modules of the same name in the library directory. This is an error unless the replacement is intended. See section Standard Modules for more information.

For information on the "installation-specific default", see documentation on the site module.

How do I find the location of Python module sources?

For a pure python module you can find the source by looking at themodule.__file__.
The datetime module, however, is written in C, and therefore datetime.__file__ points to a .so file (there is no datetime.__file__ on Windows), and therefore, you can't see the source.

If you download a python source tarball and extract it, the modules' code can be found in the Modules subdirectory.

For example, if you want to find the datetime code for python 2.6, you can look at

Python-2.6/Modules/datetimemodule.c

You can also find the latest version of this file on github on the web at
https://github.com/python/cpython/blob/main/Modules/_datetimemodule.c

How to reference python package when filename contains a period

Actually, you can import a module with an invalid name. But you'll need to use imp for that, e.g. assuming file is named models.admin.py, you could do

import imp
with open('models.admin.py', 'rb') as fp:
    models_admin = imp.load_module(
        'models_admin', fp, 'models.admin.py',
        ('.py', 'rb', imp.PY_SOURCE)
    )

But read the docs on imp.find_module and imp.load_module before you start using it.

How can I import a module dynamically given the full path?

For Python 3.5+ use (docs):

import importlib.util
import sys
spec = importlib.util.spec_from_file_location("module.name", "/path/to/file.py")
foo = importlib.util.module_from_spec(spec)
sys.modules["module.name"] = foo
spec.loader.exec_module(foo)
foo.MyClass()

For Python 3.3 and 3.4 use:

from importlib.machinery import SourceFileLoader

foo = SourceFileLoader("module.name", "/path/to/file.py").load_module()
foo.MyClass()

(Although this has been deprecated in Python 3.4.)

For Python 2 use:

import imp

foo = imp.load_source('module.name', '/path/to/file.py')
foo.MyClass()

There are equivalent convenience functions for compiled Python files and DLLs.

See also http://bugs.python.org/issue21436.

Importing modules from parent folder

It seems that the problem is not related to the module being in a parent directory or anything like that.

You need to add the directory that contains ptdraft to PYTHONPATH

You said that import nib worked with you, that probably means that you added ptdraft itself (not its parent) to PYTHONPATH.

Python can't find module in the same folder

Your code is fine, I suspect your problem is how you are launching it.

You need to launch python from your '2014_07_13_test' directory.

Open up a command prompt and 'cd' into your '2014_07_13_test' directory.

For instance:

$ cd /path/to/2014_07_13_test
$ python test.py

If you cannot 'cd' into the directory like this you can add it to sys.path

In test.py:

import sys, os
sys.path.append('/path/to/2014_07_13_test')

Or set/edit the PYTHONPATH

And all should be well...

...well there is a slight mistake with your 'shebang' lines (the first line in both your files), there shouldn't be a space between the '#' and the '!'

There is a better shebang you should use.

Also you don't need the shebang line on every file... only the ones you intend to run from your shell as executable files.

In python, how to import filename starts with a number

You could do

puzzle = __import__('8puzzle')

Very interesting problem. I'll remember not to name anything with a number.

If you'd like to import * -- you should check out this question and answer.

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