Rationale
It is not possible to retrieve the installation paths of data, or other, files for all installation schemes supported by distutils right now. I propose the inclusion of a PREFIX file within the .egg-info directory that holds information on all prefixes set at installation time and a suitable API within pkgutil.
Proposal
PREFIX
The RECORD file is a CSV file, composed of records, one line per prefix. The csv module is used to read the file, with these options:
field delimiter : ,
quoting char : "
line terminator : os.linesep (so \r\n or \n)
Each record is composed of two elements:
prefix identifier
- Prefix identifiers differentiate between the various prefixes used within the installation process.
Valid identifiers must adhere to the regular expression ^[a-z_]+, i.e any combination of lowercase ASCII characters and the underscore.
- Prefix identifiers differentiate between the various prefixes used within the installation process.
path
- The path for the prefix identifier for this distribution.
A / seperated path will be used regardless of the target system. The path definition can be either absolute or prefixed with one of the identifiers defined below. An absolute path is only used if the installation location is not relative to sys.prefix ($base) or sys.exec_prefix ($platbase).
- The path for the prefix identifier for this distribution.
Identifiers
The list of standard identifiers comprises:
$base - Base prefix
$platbase - Platform specific base prefix
$purelib - Pure Python distribution
$platlib - Non-pure Python distribution (i.e one with extensions)
$scripts - Executable Python scripts
$data - Data files
Example
Standard scheme installation on posix:
base,/usr platbase,/usr purelib,$base/lib/pythonX.Y/site-packages platlib,$platbase/lib/pythonX.Y/site-packages scripts,$base/bin data,$base/share
User scheme installation on posix:
base,/home/sirrobin/.local platbase,/home/sirrobin/.local purelib,$base/lib/pythonX.Y/site-packages platlib,$platbase/lib/pythonX.Y/site-packages scripts,$base/bin data,share
Custom installation scheme:
base,/home/sirrobin/.local platbase,/home/sirrobin/.local purelib,$base/lib/pythonX.Y/site-packages platlib,$platbase/lib/pythonX.Y/site-packages scripts,/usr/local/bin data,/usr/local/share/
Default values
Tables summarising the default values on different operating systems:
posix
Prefix identifier |
Default value: Standard scheme |
Default value: User scheme |
Environment variable |
Command line option |
$base |
sys.prefix |
~/.local |
$PYDIST_BASE |
--prefix |
$platbase |
sys.exec_prefix |
~/.local |
$PYDIST_PLATBASE |
--exec-prefix |
$purelib |
$base/lib/pythonX.Y/site-packages |
$base/lib/pythonX.Y/site-packages |
$PYDIST_PURELIB |
--install-purelib |
$platlib |
$platbase/lib/pythonX.Y/site-packages |
$platbase/lib/pythonX.Y/site-packages |
$PYDIST_PLATLIB |
--install-platlib |
$scripts |
$base/bin |
$base/bin |
$PYDIST_SCRIPTS |
--install-scripts |
$data |
$base/share |
$base/share |
$PYDIST_DATA |
--install-data |
nt
Prefix identifier |
Default value: Standard scheme |
Default value: User scheme |
Environment variable |
Command line option |
$base |
sys.prefix |
os.environ.get('%APPDATA%') |
$PYDIST_BASE |
--prefix |
$platbase |
sys.exec_prefix |
os.environ.get('%APPDATA%') |
$PYDIST_PLATBASE |
--exec-prefix |
$purelib |
$base/Python |
$base/Python/PythonXY/site-packages |
$PYDIST_PURELIB |
--install-purelib |
$platlib |
$platbase/Python |
$platbase/Python/PythonXY/site-packages |
$PYDIST_PLATLIB |
--install-platlib |
$scripts |
$base/Scripts |
$base/Python/Scripts |
$PYDIST_SCRIPTS |
--install-scripts |
$data |
$base/Data |
$base/Python/Python26 |
$PYDIST_DATA |
--install-data |
mac
os2
ce
java
riscos
API
The Distribution class will get a new attribute prefixes which holds a dictionary mapping prefix identifiers to their absolute paths.
Usage example:
>>> foo_dist = pkgutil.get_distribution('foo')
>>> foo_dist.prefixes['$base']
'/usr'
>>> foo_dist.prefixes['$data']
'/usr/share'
>>> ni_wish = open(os.path.join(foo_dist.prefixes.get('$data'), 'foo', 'shrubbery.jpg'))
>>> unladen = open(os.path.join(foo_dist.prefixes['$data'], 'foo', 'european.swallow'))