Implement framework for persistent configuration settings in INI files

mtpy/config.py

@@ -0,0 +1,107 @@
+'''Keep configuration settings for mtpy in CFG files.
+
+This module will try to load the ``mtpy.cfg`` settings file from three locations:
+the current working directory, the user's home directory, and the original
+in the package source directory (SYSTEM_CFG), in that priority. Each file
+need not contain all settings, and settings from higher priority files take
+precendence.
+
+Usage
+-----
+
+For the configuration file containing this text::
+
+    [BIRRP]
+    bbfile = Z:\instruments\bbconv.txt
+
+you can access settings like so::
+
+    >>> from MTpy.config import config
+    >>> for section_name in config.sections():
+    ...     print 'Section:', section_name
+    ...     for name, value in config.items(section_name):
+    ...         print '\t', name, ':', value
+    Section: BIRRP
+        bbfile : Z:\instruments\bbconv.txt
+
+Format
+------
+
+The settings file should be in CFG file format. See for more info:
+
+http://www.doughellmann.com/PyMOTW/ConfigParser/#accessing-configuration-settings
+
+Github
+------
+
+If for some reason the SYSTEM_CFG file is missing, load will try to download the
+original from Github, and write it as a backup 'github-mtpy.cfg' configuration
+file.
+
+'''
+import ConfigParser
+import os
+import shutil
+import urllib2
+
+CFG_FN = 'mtpy.cfg'
+
+# Possible locations for CFG files
+
+GITHUB_CFG = os.path.join(os.path.dirname(__file__), 'github-' + CFG_FN)
+SYSTEM_CFG = os.path.join(os.path.dirname(__file__), CFG_FN)
+USER_CFG = os.path.join(os.path.expanduser('~'), CFG_FN)
+WORKINGDIR_CFG = os.path.join(os.getcwd(), CFG_FN)
+
+
+def load():
+    '''Return config parser.
+
+    Checks for GITHUB_CFG, SYSTEM_CFG, USER_CFG, and WORKINGDIR_CFG and updates
+    the parser object with the values found each time.
+
+    '''
+    def combine(parsers):
+        '''Return a new SafeConfigParser containing the options already set in
+        *parsers*.
+
+        Works forwards through the list, so the higher priority parsers should go
+        at the end of *parsers*.
+
+        '''
+        new_parser = ConfigParser.SafeConfigParser()
+        for parser in parsers:
+            if not parser:
+                continue
+            for section in parser.sections():
+                if not new_parser.has_section(section):
+                    new_parser.add_section(section)
+                for name, value in parser.items(section):
+                    new_parser.set(section, name, str(value))
+        return new_parser
+
+    def make_parser(fn):
+        parser = ConfigParser.SafeConfigParser()
+        parser.read(fn)
+        return parser
+
+    parser = make_parser(GITHUB_CFG)
+    read_at_least_one = False
+    for fn in [SYSTEM_CFG, USER_CFG, WORKINGDIR_CFG]:
+        next_parser = make_parser(fn)
+        if next_parser.read(fn):
+            read_at_least_one = True
+            parser = combine([parser, next_parser])
+
+    if not read_at_least_one:
+        # Failed to read any CFG file. This is bad, so try to retrieve the
+        # latest default from Github, and copy it to SYSTEM_CFG.
+
+        github_cfg_url = urllib2.url('http://raw.github.com/geophysics/mtpy/master/mtpy/' + CFG_FN)
+        with open(GITHUB_CFG, mode='w') as f:
+            f.write(github_cfg_url.read())
+        return parser.read([GITHUB_CFG])
+    return parser
+
+
+config = load()