FAQ
Hi,

I'm trying to get into the object oriented aspect of Python. If I create
a custom class (in it's own file), how do I access that class in a
function in a different file? In Java there's the notion of a CLASSPATH,
where you can tell the compiler to look for classes. Is there something
similar to this in Python?

Thanks,

Dave

Search Discussions

  • Jepler at Nov 1, 2005 at 2:40 am
    This section of the tutorial discusses the module search path:
    http://docs.python.org/tut/node8.html

    6.1.1 The Module Search Path

    When a module named spam is imported, the interpreter searches for a file named
    spam.py in the current directory, and then in the list of directories specified
    by the environment variable PYTHONPATH. This has the same syntax as the shell
    variable PATH, that is, a list of directory names. When PYTHONPATH is not set,
    or when the file is not found there, the search continues in an installation-
    dependent default path; on Unix, this is usually .:/usr/local/lib/python.

    Actually, modules are searched in the list of directories given by the variable
    sys.path which is initialized from the directory containing the input script
    (or the current directory), PYTHONPATH and the installation-dependent default.
    This allows Python programs that know what they're doing to modify or replace
    the module search path. Note that because the directory containing the script
    being run is on the search path, it is important that the script not have the
    same name as a standard module, or Python will attempt to load the script as a
    module when that module is imported. This will generally be an error. See
    section 6.2, ``Standard Modules,'' for more information.

    Jeff
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  • David Wahler at Nov 1, 2005 at 2:47 am

    David Mitchell wrote:
    Hi,

    I'm trying to get into the object oriented aspect of Python. If I create
    a custom class (in it's own file), how do I access that class in a
    function in a different file? In Java there's the notion of a CLASSPATH,
    where you can tell the compiler to look for classes. Is there something
    similar to this in Python?

    Thanks,

    Dave
    Python is a little different than Java in this respect. Whereas Java
    loads code one public class at a time, Python loads it in modules,
    where a module is (generally speaking) one source file.

    Say you have a file, foo.py:
    ###############################
    class Xyz:
    def do_stuff(self):
    pass

    class Abc:
    def do_more_stuff(self):
    pass
    ###############################

    Then in another file, inserting the statement "import foo" will execute
    foo.py and make its global variables available as part of an object
    called "foo". There is no automatic loading by class and package name
    like Java does it. Once you've done this, you can access the members
    using expressions such as "foo.Xyz" e.g. "foo.Xyz().do_stuff()".

    As for the search path: sys.path (the path attribute of the sys module)
    is a list of directories which are searched, in order, for modules
    specified by "import". By default this is the current directory
    followed by a few standard Python library directories; most of the time
    you shouldn't need to change it, at least for simple projects.

    Hope this helps,

    -- David

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