configpa.py

minimal python variant for small footprint apps like embedded apps

"""Configuration file parser.

A setup file consists of sections, lead by a "[section]" header,
and followed by "name: value" entries, with continuations and such in
the style of RFC 822.

The option values can contain format strings which refer to other values in
the same section, or values in a special [DEFAULT] section.

For example:

    something: %(dir)s/whatever

would resolve the "%(dir)s" to the value of dir.  All reference
expansions are done late, on demand.

Intrinsic defaults can be specified by passing them into the
ConfigParser constructor as a dictionary.

class:

ConfigParser -- responsible for for parsing a list of
                configuration files, and managing the parsed database.

    methods:

    __init__(defaults=None)
        create the parser and specify a dictionary of intrinsic defaults.  The
        keys must be strings, the values must be appropriate for %()s string
        interpolation.  Note that `__name__' is always an intrinsic default;
        it's value is the section's name.

    sections()
        return all the configuration section names, sans DEFAULT

    options(section)
        return list of configuration options for the named section

    read(filenames)
        read and parse the list of named configuration files

    get(section, option, raw=0, vars=None)
        return a string value for the named option.  All % interpolations are
        expanded in the return values, based on the defaults passed into the
        constructor and the DEFAULT section.  Additional substitutions may be
        provided using the `vars' argument, which must be a dictionary whose
        contents override any pre-existing defaults.

    getint(section, options)
        like get(), but convert value to an integer

    getfloat(section, options)
        like get(), but convert value to a float

    getboolean(section, options)
        like get(), but convert value to a boolean (currently defined as 0 or
        1, only)
"""

import sys
import string
import re

DEFAULTSECT = "DEFAULT"



# exception classes
class Error:
    def __init__(self, msg=''):
        self._msg = msg
    def __repr__(self):
        return self._msg

class NoSectionError(Error):
    def __init__(self, section):
        Error.__init__(self, 'No section: %s' % section)
        self.section = section

class DuplicateSectionError(Error):
    def __init__(self, section):
        Error.__init__(self, "Section %s already exists" % section)
        self.section = section

class NoOptionError(Error):
    def __init__(self, option, section):
        Error.__init__(self, "No option `%s' in section: %s" %
                       (option, section))
        self.option = option
        self.section = section

class InterpolationError(Error):
    def __init__(self, reference, option, section, rawval):
        Error.__init__(self,
                       "Bad value substitution:\n"
                       "\tsection: [%s]\n"
                       "\toption : %s\n"
                       "\tkey    : %s\n"
                       "\trawval : %s\n"
                       % (section, option, reference, rawval))
        self.reference = reference
        self.option = option
        self.section = section

class MissingSectionHeaderError(Error):
    def __init__(self, filename, lineno, line):
        Error.__init__(
            self,
            'File contains no section headers.\nfile: %s, line: %d\n%s' %
            (filename, lineno, line))
        self.filename = filename
        self.lineno = lineno
        self.line = line

class ParsingError(Error):
    def __init__(self, filename):
        Error.__init__(self, 'File contains parsing errors: %s' % filename)
        self.filename = filename
        self.errors = []

    def append(self, lineno, line):
        self.errors.append((lineno, line))
        self._msg = self._msg + '\n\t[line %2d]: %s' % (lineno, line)



class ConfigParser:
    def __init__(self, defaults=None):
        self.__sections = {}
        if defaults is None:
            self.__defaults = {}
        else:
            self.__defaults = defaults

    def defaults(self):
        return self.__defaults

    def sections(self):
        """Return a list of section names, excluding [DEFAULT]"""
        # self.__sections will never have [DEFAULT] in it
        return self.__sections.keys()

    def add_section(self, section):
        """Create a new section in the configuration.

        Raise DuplicateSectionError if a section by the specified name
        already exists.
        """
        if self.__sections.has_key(section):
            raise DuplicateSectionError(section)
        self.__sections[section] = {}

    def has_section(self, section):
        """Indicate whether the named section is present in the configuration.

        The DEFAULT section is not acknowledged.
        """
        return self.__sections.has_key(section)

    def options(self, section):
        try:
            opts = self.__sections[section].copy()
        except KeyError:
            raise NoSectionError(section)
        opts.update(self.__defaults)
        return opts.keys()

    def read(self, filenames):
        """Read and parse a list of filenames."""
        if type(filenames) is type(''):
            filenames = [filenames]
        for file in filenames:
            try:
                fp = open(file, 'r')
                self.__read(fp)
            except IOError:
                pass

    def get(self, section, option, raw=0, vars=None):
        """Get an option value for a given section.

        All % interpolations are expanded in the return values, based on the
        defaults passed into the constructor, unless the optional argument
        `raw' is true.  Additional substitutions may be provided using the
        `vars' argument, which must be a dictionary whose contents overrides
        any pre-existing defaults.

        The section DEFAULT is special.
        """
        try:
            sectdict = self.__sections[section].copy()
        except KeyError:
            if section == DEFAULTSECT:
                sectdict = {}
            else:
                raise NoSectionError(section)
        d = self.__defaults.copy()
        d.update(sectdict)
        # Update with the entry specific variables
        if vars:
            d.update(vars)
        option = string.lower(option)
        try:
            rawval = d[option]
        except KeyError:
            raise NoOptionError(option, section)
        # do the string interpolation
        if raw:
            return rawval

        value = rawval                  # Make it a pretty variable name
        depth = 0                       
        while depth < 10:               # Loop through this until it's done
            depth = depth + 1
            if not string.find(value, "%("):
                try:
                    value = value % d
                except KeyError, key:
                    raise InterpolationError(key, option, section, rawval)
            else:
                return value
    
    def __get(self, section, conv, option):
        return conv(self.get(section, option))

    def getint(self, section, option):
        return self.__get(section, string.atoi, option)

    def getfloat(self, section, option):
        return self.__get(section, string.atof, option)

    def getboolean(self, section, option):
        v = self.get(section, option)
        val = string.atoi(v)
        if val not in (0, 1):
            raise ValueError, 'Not a boolean: %s' % v
        return val

    #
    # Regular expressions for parsing section headers and options.  Note a
    # slight semantic change from the previous version, because of the use
    # of \w, _ is allowed in section header names.
    __SECTCRE = re.compile(
        r'\['                                 # [
        r'(?P<header>[-\w]+)'                 # `-', `_' or any alphanum
        r'\]'                                 # ]
        )
    __OPTCRE = re.compile(
        r'(?P<option>[-.\w]+)'                # - . _ alphanum
        r'[ \t]*[:=][ \t]*'                   # any number of space/tab,
                                              # followed by separator
                                              # (either : or =), followed
                                              # by any # space/tab
        r'(?P<value>.*)$'                     # everything up to eol
        )

    def __read(self, fp):
        """Parse a sectioned setup file.

        The sections in setup file contains a title line at the top,
        indicated by a name in square brackets (`[]'), plus key/value
        options lines, indicated by `name: value' format lines.
        Continuation are represented by an embedded newline then
        leading whitespace.  Blank lines, lines beginning with a '#',
        and just about everything else is ignored.
        """
        cursect = None                            # None, or a dictionary
        optname = None
        lineno = 0
        e = None                                  # None, or an exception
        while 1:
            line = fp.readline()
            if not line:
                break
            lineno = lineno + 1
            # comment or blank line?
            if string.strip(line) == '' or line[0] in '#;':
                continue
            if string.lower(string.split(line)[0]) == 'rem' \
               and line[0] == "r":      # no leading whitespace
                continue
            # continuation line?
            if line[0] in ' \t' and cursect is not None and optname:
                value = string.strip(line)
                if value:
                    cursect[optname] = cursect[optname] + '\n ' + value
            # a section header or option header?
            else:
                # is it a section header?
                mo = self.__SECTCRE.match(line)
                if mo:
                    sectname = mo.group('header')
                    if self.__sections.has_key(sectname):
                        cursect = self.__sections[sectname]
                    elif sectname == DEFAULTSECT:
                        cursect = self.__defaults
                    else:
                        cursect = {'__name__': sectname}
                        self.__sections[sectname] = cursect
                    # So sections can't start with a continuation line
                    optname = None
                # no section header in the file?
                elif cursect is None:
                    raise MissingSectionHeaderError(fp.name, lineno, `line`)
                # an option line?
                else:
                    mo = self.__OPTCRE.match(line)
                    if mo:
                        optname, optval = mo.group('option', 'value')
                        optname = string.lower(optname)
                        optval = string.strip(optval)
                        # allow empty values
                        if optval == '""':
                            optval = ''
                        cursect[optname] = optval
                    else:
                        # a non-fatal parsing error occurred.  set up the
                        # exception but keep going. the exception will be
                        # raised at the end of the file and will contain a
                        # list of all bogus lines
                        if not e:
                            e = ParsingError(fp.name)
                        e.append(lineno, `line`)
        # if any parsing errors occurred, raise an exception
        if e:
            raise e