Lib/configparser.py (part 2)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/configparser.py ↗

This annotation covers value interpolation, file writing, and the DEFAULT section fallback. See lib_configparser_detail for read(), get(), set(), and section management.

Map

Lines	Symbol	Role
1-80	Interpolation base	before_get hook called by get()
81-200	BasicInterpolation	%(key)s substitution within the same section
201-350	ExtendedInterpolation	${section:key} cross-section substitution
351-500	write()	Serialize the config back to a file
501-650	DEFAULT section	Fallback values for all sections
651-800	Converters	getint, getfloat, getboolean, custom converters
801-1400	RawConfigParser._read	Parser state machine for the INI format

Reading

BasicInterpolation

# CPython: Lib/configparser.py:390 BasicInterpolation
class BasicInterpolation(Interpolation):
    """%(key)s substitution within the current section (+ DEFAULT)."""
    def before_get(self, parser, section, option, value, vars):
        L = []
        self._interpolate_some(parser, option, L, value, section, vars, 1)
        return ''.join(L)

    def _interpolate_some(self, parser, option, accum, rest, section, map, depth):
        if depth > MAX_INTERPOLATION_DEPTH:
            raise InterpolationDepthError(option, section, rest)
        while rest:
            p = rest.find('%')
            if p < 0:
                accum.append(rest); return
            accum.append(rest[:p])
            rest = rest[p:]
            if rest[1:2] == '(':
                m = self._KEYCRE.match(rest)
                var = parser.get(section, m.group(1), raw=True, vars=map)
                self._interpolate_some(parser, option, accum, var,
                                       section, map, depth + 1)
                rest = rest[m.end():]

ExtendedInterpolation

# CPython: Lib/configparser.py:470 ExtendedInterpolation
class ExtendedInterpolation(Interpolation):
    """${section:key} substitution across sections."""
    _KEYCRE = re.compile(r'\$\{([^}]+)\}')

    def before_get(self, parser, section, option, value, vars):
        L = []
        self._interpolate_some(parser, option, L, value, section, vars, 1)
        return ''.join(L)

    def _interpolate_some(self, parser, option, accum, rest, section, map, depth):
        ...
        # ${section:option} → parser.get(section, option)
        # ${option} → parser.get(section, option)  (same section)

write()

# CPython: Lib/configparser.py:560 RawConfigParser.write
def write(self, fp, space_around_delimiters=True):
    """Write the configuration to a file-like object."""
    if space_around_delimiters:
        d = ' {} '.format(self._delimiters[0])
    else:
        d = self._delimiters[0]
    if self._defaults:
        self._write_section(fp, self.default_section,
                            self._defaults.items(), d)
    for section in self._sections:
        self._write_section(fp, section,
                            self._sections[section].items(), d)

DEFAULT section fallback

# CPython: Lib/configparser.py:700 SectionProxy.__getitem__
# get() merges DEFAULT values into the section's own values:
# vars: explicit overrides
# section values
# DEFAULT fallback
# If key not found in any: raise NoOptionError

DEFAULT (case-insensitive) is special: its keys are available in all sections as fallback values but do not appear in sections().

Custom converters

# CPython: Lib/configparser.py:780 converters
# RawConfigParser(converters={'list': lambda v: v.split(',')})
# Automatically creates parser.getlist(section, option)

gopy notes

configparser is pure Python. BasicInterpolation is the default; ExtendedInterpolation must be passed explicitly. write() uses print() which uses sys.stdout's write() method, backed by gopy's file object.