Allen Fowler wrote:
What is the recommended way to configure my application find the various
database and/or configuration files it needs?
Recommemded by whom? A lot depends on the OS. Apple for example have one set of
recommendations for MacOS, Windows has another and Linux has several to choose
from!
Thank you.... good point.
Planning on using a ConfigParser based .ini file located in the ./config folder.
For instance my folder layout:
/path_to_app/app.py
/path_to_app/lib/
/path_to_app/database/
/path_to_app/config/
/path_to_app/photos
.... and so on. I would like to make an .ini in the config folder
Seems fair enough, however on a Unix system you should also consider allowing
the user to have their own personalised version in their home directory. Thus at
startup you get the current user ID / home directory and look for a suitable
config file. If it exists read it, if not read the default one in your config
directory.
1) How does my main app file find the config file in the first place?
Generally use a relative path so normally your app will run from its home folder
so you can look in ./config. You might also set a system environment variable -
for example the CLASSPATH or PYTHONPATH variables, or the ORACLE_HOME used by
Oracle for their database. If the environment var is not set then look in
./config
Assuming the application could be invoked in odd ways that may alter the notion
of the current working directory, how do I unambiguously find the absolute path
to the current python source file? (So I can load the nearby .ini)
As a follow-up question, how do give my modules stored under ./lib access to
the data in my ConfigParser object? (For instance, database connection string,
storage path, etc.)
I guess a global ConfigParser object would work, but that seems wrong.
Regardless of the OS, you need to consider whether more than one user is
going to share the code and constant data, but have independent versions
of the variable data. If so, then putting the .ini file in the code
tree makes no sense. You also have to decide whether there is going to
be an install process, or whether the program files will be simply
unzipped or copied to a single target directory. And if there is an
install, the library you use could very likely influence what you wind
up doing.
But for raw answers: you can tell where a running python module is
located, simply by using the __file__ attribute. You can then parse
this with os.path.dirname() to get the directory the file is located
in. Then you can use ..\config to get to the config directory. You're
right; don't use current directory to find any of this. Use it to find
user data, usually, if the command is entered interactively. And don't
use it at all, for things started by Explorer (in Windows).
I would expect to have two directory structures, one fixed, and one
variable. The fixed one is stuff that doesn't get modified once
install (or copy) is complete. And the variable one is derived in some
way from the user's login. On Windows, that could be a registry entry
(HKCU), or it could be the HOMEPATH ( c:\Documents and
Settings\username, on XP ). Once you've calculated this initial
variable directory, create an INI file that says where all the rest of
the variable data is. I claim that this would be an absolute path, set
up the first time the user runs File->Configuration. The default
would be relative to the same directory, but it should be changeable.
I try to set up my personal systems with two main partitions. One has
(mostly) constant data and programs, modified each install. It also has
junk, like temp files, the swapfile, etc. All user data is on a
different partition, with very different backup rules. Windows puts my
HOMEPATH on the C: drive, but I avoid programs that force me to leave
any quantity of information there.
As for how various library modules should find data gathered in your
main script, you just pass an instance of the object containing that data.
DaveA
_______________________________________________
Tutor maillist - Tutor@python.org
http://mail.python.org/mailman/listinfo/tutor
