# By default, you can't. When importing a file, Python only 
# searches the current directory, the directory that the 
# entry-point script is running from, and sys.path which includes
# locations such as the package installation directory 
# (it's actually a little more complex than this, but this covers
# most cases).

# you can however, add to the path at runtime

import sys
# insert at position 1 in the path, as 0 is the path of this file.
sys.path.insert(1, '/path/to/application/app/folder')

import file

file.function()