what does __file__ mean in a python file

[selfboot]

From http://stackoverflow.com/questions/9271464/what-does-the-file-variable-mean-do :

I just want to address some confusion first. __file__ is not a wildcard it is an attribute. Double underscore attributes and methods are considered to be "special" by convention and serve a special purpose.

http://docs.python.org/reference/datamodel.html shows many of the special methods and attributes, if not all of them.

In this case __file__ is an attribute of a module (a module object). In Python a .py file is a module. So import a module will have an attribute of __file__ which means different things under difference circumstances.

Taken from the docs:

__file__ is the pathname of the file from which the module was loaded, if it was loaded from a file. The file attribute is not present for C modules that are statically linked into the interpreter; for extension modules loaded dynamically from a shared library, it is the pathname of the shared library file.

[selfboot]

Model

A module is a file containing Python definitions and statements. The file name is the module name with the suffix .py appended.

When you run a Python module with

python fibo.py <arguments>

the code in the module will be executed, just as if you imported it, but with the __name__ set to "__main__".

__file__ in model

For the demo.py

#! /usr/bin/env python
# -*- coding: utf-8 -*-

import os
print "__file__:", __file__
print "__cwd__:", os.getcwd()

print os.path.dirname(__file__)
print os.path.realpath(__file__)

print "*"*10, "dirname:"
print os.path.dirname(os.path.realpath(__file__))
print os.path.abspath(os.path.dirname(__file__))

Run directly from the script's directory：

$ python demo.py
__file__: demo.py
__cwd__: /Users/f/dropbox

/Users/f/dropbox/demo.py
********** dirname:
/Users/f/dropbox
/Users/f/dropbox

Run from the script's parent directory：：

$ python dropbox/demo.py
__file__: dropbox/demo.py
__cwd__: /Users/f
dropbox
/Users/f/dropbox/demo.py
********** dirname:
/Users/f/dropbox
/Users/f/dropbox

[selfboot]

From http://stackoverflow.com/questions/5137497/find-current-directory-and-files-directory

Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.

So, for demo.py as follows:

#! /usr/bin/env python
# -*- coding: utf-8 -*-

import os
print "__file__:", __file__
print "__cwd__:", os.getcwd()

print os.path.dirname(__file__)
print os.path.realpath(__file__)

# change the current working directory.
os.chdir("/home/")
print "__file__:", __file__
print "__cwd__:", os.getcwd()
print os.path.dirname(__file__)
print os.path.realpath(__file__)

Run as:

$ python dropbox/demo.py
__file__: dropbox/demo.py
__cwd__: /Users/feizhao
dropbox
/Users/feizhao/dropbox/demo.py
__file__: dropbox/demo.py
__cwd__: /home
dropbox
/home/dropbox/demo.py