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Lib/configparser.py (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/configparser.py

This annotation covers the reading and interpolation machinery. See lib_configparser2_detail for ConfigParser.__init__, get, set, and the section/option model.

Map​

LinesSymbolRole
1-80ConfigParser.readRead one or more filenames into the config
81-180_readLine-by-line parser: sections, options, continuations
181-280BasicInterpolation%(name)s substitution
281-380ExtendedInterpolation${section:option} substitution
381-500RawConfigParser.getRetrieve without interpolation

Reading​

_read​

# CPython: Lib/configparser.py:1050 RawConfigParser._read
def _read(self, fp, fpname):
    cursect = None  # current section dict
    sectname = None
    optname = None
    lineno = 0
    indent_level = 0
    e = None  # exception accumulator

    for lineno, line in enumerate(fp, start=1):
        # Skip comment lines and blank lines
        if not line.strip() or line[0] in self._comment_prefixes:
            if self._empty_lines_in_values:
                if (cursect is not None and optname and
                        cursect[optname] is not None):
                    cursect[optname].append('')
            else:
                indent_level = sys.maxsize
            continue
        # Continuation line
        first_nonspace = NONSPACECRE.search(line)
        cur_indent_level = first_nonspace.start() if first_nonspace else 0
        if (cursect is not None and optname and
                cur_indent_level > indent_level):
            cursect[optname].append(line.rstrip())
        # Section header
        elif line[0] == '[':
            ...
        # Option line
        else:
            ...

The parser is line-by-line with explicit state (cursect, optname). Multi-line values are continuation lines that start with more indentation than the key line. Comments can appear on their own lines only (inline comments require inline_comment_prefixes).

BasicInterpolation​

# CPython: Lib/configparser.py:390 BasicInterpolation.before_get
class BasicInterpolation(Interpolation):
    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)
                break
            accum.append(rest[:p])
            rest = rest[p:]
            if rest[1:2] == '(':
                # %(name)s substitution
                m = self._KEYCRE.match(rest)
                var = parser.get(section, m.group(1), raw=True, vars=vars)
                rest = m.group(2) + rest[m.end():]
                self._interpolate_some(parser, option, accum, var, section, map, depth + 1)
            elif rest[1:2] == '%':
                accum.append('%')
                rest = rest[2:]

BasicInterpolation handles %(name)s where name refers to another option in the same section (or DEFAULT). Recursive references are detected with a depth counter; depth > 10 raises InterpolationDepthError.

ExtendedInterpolation​

# CPython: Lib/configparser.py:440 ExtendedInterpolation.before_get
class ExtendedInterpolation(Interpolation):
    def before_get(self, parser, section, option, value, vars):
        L = []
        self._interpolate_some(parser, option, L, value, section, vars, 1)
        return ''.join(L)
    # Uses ${section:option} or ${option} (current section)

ExtendedInterpolation supports cross-section references: ${paths:base}/file.txt pulls base from the [paths] section. This enables a more INI-like inheritance pattern than BasicInterpolation.

gopy notes​

ConfigParser is in module/configparser/module.go. _read iterates lines with Go bufio.Scanner. BasicInterpolation is a Go struct with BeforeGet method. Recursive depth is tracked with an integer counter passed through calls.