[Tutor] Configuaration files and paths?

[Martin Walsh]

Allen Fowler wrote:
>>> FWIW:
>>>
>>> When using relative paths I got extra ../../ terms, so I changed  
>> join_relative() to:
>>> def join_relative(base, path):
>>>     return os.path.normpath(os.path.join(script_dir(base), path))
>>>
>>>
>>> Seems to work...
>>
>> Yeah, good catch ... looks great, and thanks for sharing your mod.
>>
> 
> 
> Glad I could return the favor.  :)
> 
> Since then, I took it a bit further for use in my code...  I am not finished with it yet, but am curios what you think.  (I am not sure named things right or structured it logically....)
> 
> 
> ###################
> 
> import os
> class HomePath(object):
>         """For finding paths based on a home/install directory.
>         
>         """
>          
>         def __init__(self, home_dir = None, home_file = None):
>             """Must be called with either a path to a directory or, as a shortcut, a file in that directory.
>             
>             """
>             
>             if home_file != None:
>                 # Set home based on a path to a file in its directory
>                 self.home = os.path.normpath(self.fix_path(home_file))
>             
>             elif home_dir != None:
>                 # Set home based on its path
>                 self.home = os.path.normpath(self.get_dir(home_dir))
>                 
>             else:
>                 raise Exception("Must call with either a path to a directory or, as a shortcut, a file in that directory.")
>                 
>         def abs(self, rel_from_home):
>             """Return an absolute path when passed a path relative to home.
>             
>             """
>             
>             return self.join_relative(self.home, rel_from_home)
>             
>         def fix_path(self, base):
>             return os.path.realpath(os.path.abspath(base))
> 
>         def get_dir(self, base):
>             return os.path.dirname(self.fix_path(base))
> 
>         def join_relative(self, base, path):
>             return os.path.normpath(self.fix_path(os.path.join(self.home, path)))
> #############################

I'm not sure I understand your end goal, given the args to __init__. I'd
guess, perhaps incorrectly, that you may be trying to shoehorn
conflicting purposes.

If your only aim is to calculate an absolute path to a resource's
parent, or home, folder then your class can be simplified a lot, IMHO.
Specifically, I don't see a reason to differentiate between home_dir and
home_file. Please feel free to clarify if I'm missing the point.

import os

class HomePath(object):
    def __init__(self, path):
        # fix_path and get_dir on base path
        self.home = os.path.dirname(
            os.path.realpath(
                os.path.abspath(path)
            )
        )

    def join(self, relative_path):
        return os.path.normpath(os.path.join(self.home, relative_path))


Also, have a look at
http://docs.python.org/library/os.path.html#os.path.abspath

... the main point is that your initial path element must have enough
information in it to construct an abspath, otherwise os.getcwd() can
pollute the calculation. I believe if you use __file__ you're good, and
sys.argv[0], while potentially relative in nature should always be
relative to os.getcwd() AFAICT, so you're good there too. Otherwise
avoid constructing a HomePath object with a relative start path.

HTH,
Marty