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gh-159684: Modernize string formatting and simplify constructs in configparser #159687

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2db122c
gh-159684: Use f-strings in configparser and its tests
jaraco Oct 18, 2026
3a49bcb
gh-159684: Simplify a few constructs in configparser and its tests
jaraco Oct 18, 2026
a63f02d
gh-159684: Convert the last percent-formatting in configparser
jaraco Oct 18, 2026
105bdde
gh-159684: Clear the remaining Ruff findings in configparser
jaraco Oct 18, 2026
c45a20e
gh-159684: Add a NEWS entry
jaraco Oct 18, 2026
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141 changes: 80 additions & 61 deletions Lib/configparser.py
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Original file line number Diff line number Diff line change
Expand Up @@ -143,27 +143,50 @@
between keys and values are surrounded by spaces.
"""

# Do not import dataclasses; overhead is unacceptable (gh-117703)
# Defer annotations so that typing need not be imported at runtime.
from __future__ import annotations

from collections.abc import Iterable, MutableMapping
from collections import ChainMap as _ChainMap
# Do not import dataclasses; overhead is unacceptable (gh-117703)
import contextlib
import functools
import io
import itertools
import os
import re
import sys
from collections import ChainMap as _ChainMap
from collections.abc import Iterable, MutableMapping

__all__ = ("NoSectionError", "DuplicateOptionError", "DuplicateSectionError",
"NoOptionError", "InterpolationError", "InterpolationDepthError",
"InterpolationMissingOptionError", "InterpolationSyntaxError",
"ParsingError", "MissingSectionHeaderError",
"MultilineContinuationError", "UnnamedSectionDisabledError",
"InvalidWriteError", "ConfigParser", "RawConfigParser",
"Interpolation", "BasicInterpolation", "ExtendedInterpolation",
"SectionProxy", "ConverterMapping",
"DEFAULTSECT", "MAX_INTERPOLATION_DEPTH", "UNNAMED_SECTION")
# Do not import typing either; it is only needed for annotations.
TYPE_CHECKING = False
if TYPE_CHECKING:
from typing import ClassVar

__all__ = (
"DEFAULTSECT",
"MAX_INTERPOLATION_DEPTH",
"UNNAMED_SECTION",
"BasicInterpolation",
"ConfigParser",
"ConverterMapping",
"DuplicateOptionError",
"DuplicateSectionError",
"ExtendedInterpolation",
"Interpolation",
"InterpolationDepthError",
"InterpolationError",
"InterpolationMissingOptionError",
"InterpolationSyntaxError",
"InvalidWriteError",
"MissingSectionHeaderError",
"MultilineContinuationError",
"NoOptionError",
"NoSectionError",
"ParsingError",
"RawConfigParser",
"SectionProxy",
"UnnamedSectionDisabledError",
)

_default_dict = dict
DEFAULTSECT = "DEFAULT"
Expand All @@ -190,7 +213,7 @@ class NoSectionError(Error):
"""Raised when no section matches a requested option."""

def __init__(self, section):
Error.__init__(self, 'No section: %r' % (section,))
Error.__init__(self, f'No section: {section!r}')
self.section = section
self.args = (section, )

Expand All @@ -208,7 +231,7 @@ def __init__(self, section, source=None, lineno=None):
if source is not None:
message = ["While reading from ", repr(source)]
if lineno is not None:
message.append(" [line {0:2d}]".format(lineno))
message.append(f" [line {lineno:2d}]")
message.append(": section ")
message.extend(msg)
msg = message
Expand All @@ -234,7 +257,7 @@ def __init__(self, section, option, source=None, lineno=None):
if source is not None:
message = ["While reading from ", repr(source)]
if lineno is not None:
message.append(" [line {0:2d}]".format(lineno))
message.append(f" [line {lineno:2d}]")
message.append(": option ")
message.extend(msg)
msg = message
Expand All @@ -252,8 +275,7 @@ class NoOptionError(Error):
"""A requested option was not found."""

def __init__(self, option, section):
Error.__init__(self, "No option %r in section: %r" %
(option, section))
Error.__init__(self, f"No option {option!r} in section: {section!r}")
self.option = option
self.section = section
self.args = (option, section)
Expand All @@ -273,9 +295,9 @@ class InterpolationMissingOptionError(InterpolationError):
"""A string substitution required a setting which was not available."""

def __init__(self, option, section, rawval, reference):
msg = ("Bad value substitution: option {!r} in section {!r} contains "
"an interpolation key {!r} which is not a valid option name. "
"Raw value: {!r}".format(option, section, reference, rawval))
msg = (f"Bad value substitution: option {option!r} in section "
f"{section!r} contains an interpolation key {reference!r} "
f"which is not a valid option name. Raw value: {rawval!r}")
InterpolationError.__init__(self, option, section, msg)
self.reference = reference
self.args = (option, section, rawval, reference)
Expand All @@ -293,11 +315,10 @@ class InterpolationDepthError(InterpolationError):
"""Raised when substitutions are nested too deeply."""

def __init__(self, option, section, rawval):
msg = ("Recursion limit exceeded in value substitution: option {!r} "
"in section {!r} contains an interpolation key which "
"cannot be substituted in {} steps. Raw value: {!r}"
"".format(option, section, MAX_INTERPOLATION_DEPTH,
rawval))
msg = (f"Recursion limit exceeded in value substitution: option "
f"{option!r} in section {section!r} contains an interpolation "
f"key which cannot be substituted in "
f"{MAX_INTERPOLATION_DEPTH} steps. Raw value: {rawval!r}")
InterpolationError.__init__(self, option, section, msg)
self.args = (option, section, rawval)

Expand Down Expand Up @@ -327,7 +348,7 @@ def combine(self, others):
return self

@staticmethod
def _raise_all(exceptions: Iterable['ParsingError']):
def _raise_all(exceptions: Iterable[ParsingError]):
"""
Combine any number of ParsingErrors into one and raise it.
"""
Expand All @@ -343,8 +364,8 @@ class MissingSectionHeaderError(ParsingError):
def __init__(self, filename, lineno, line):
Error.__init__(
self,
'File contains no section headers.\nfile: %r, line: %d\n%r' %
(filename, lineno, line))
'File contains no section headers.\n'
f'file: {filename!r}, line: {lineno:d}\n{line!r}')
self.source = filename
self.lineno = lineno
self.line = line
Expand All @@ -357,8 +378,7 @@ def __init__(self, filename, lineno, line):
Error.__init__(
self,
"Key without value continued with an indented line.\n"
"file: %r, line: %d\n%r"
%(filename, lineno, line))
f"file: {filename!r}, line: {lineno:d}\n{line!r}")
self.source = filename
self.lineno = lineno
self.line = line
Expand Down Expand Up @@ -437,8 +457,8 @@ def before_set(self, parser, section, option, value):
tmp_value = value.replace('%%', '') # escaped percent signs
tmp_value = self._KEYCRE.sub('', tmp_value) # valid syntax
if '%' in tmp_value:
raise ValueError("invalid interpolation syntax in %r at "
"position %d" % (value, tmp_value.find('%')))
raise ValueError(f"invalid interpolation syntax in {value!r} "
f"at position {tmp_value.find('%'):d}")
return value

def _interpolate_some(self, parser, option, accum, rest, section, map,
Expand All @@ -463,7 +483,7 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
m = self._KEYCRE.match(rest)
if m is None:
raise InterpolationSyntaxError(option, section,
"bad interpolation variable reference %r" % rest)
f"bad interpolation variable reference {rest!r}")
var = parser.optionxform(m.group(1))
rest = rest[m.end():]
try:
Expand All @@ -479,8 +499,8 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
else:
raise InterpolationSyntaxError(
option, section,
"'%%' must be followed by '%%' or '(', "
"found: %r" % (rest,))
"'%' must be followed by '%' or '(', "
f"found: {rest!r}")


class ExtendedInterpolation(Interpolation):
Expand All @@ -498,12 +518,12 @@ def before_set(self, parser, section, option, value):
tmp_value = value.replace('$$', '') # escaped dollar signs
tmp_value = self._KEYCRE.sub('', tmp_value) # valid syntax
if '$' in tmp_value:
raise ValueError("invalid interpolation syntax in %r at "
"position %d" % (value, tmp_value.find('$')))
raise ValueError(f"invalid interpolation syntax in {value!r} "
f"at position {tmp_value.find('$'):d}")
return value

def _interpolate_some(self, parser, option, accum, rest, section, map,
depth):
def _interpolate_some(self, parser, option, # noqa: C901 # gh-159686
accum, rest, section, map, depth):
rawval = parser.get(section, option, raw=True, fallback=rest)
if depth > MAX_INTERPOLATION_DEPTH:
raise InterpolationDepthError(option, section, rawval)
Expand All @@ -524,7 +544,7 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
m = self._KEYCRE.match(rest)
if m is None:
raise InterpolationSyntaxError(option, section,
"bad interpolation variable reference %r" % rest)
f"bad interpolation variable reference {rest!r}")
path = m.group(1).split(':')
rest = rest[m.end():]
sect = section
Expand All @@ -540,7 +560,7 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
else:
raise InterpolationSyntaxError(
option, section,
"More than one ':' found: %r" % (rest,))
f"More than one ':' found: {rest!r}")
except (KeyError, NoSectionError, NoOptionError):
raise InterpolationMissingOptionError(
option, section, rawval, ":".join(path)) from None
Expand All @@ -556,7 +576,7 @@ def _interpolate_some(self, parser, option, accum, rest, section, map,
raise InterpolationSyntaxError(
option, section,
"'$' must be followed by '$' or '{', "
"found: %r" % (rest,))
f"found: {rest!r}")


class _ReadState:
Expand All @@ -570,7 +590,7 @@ class _ReadState:

def __init__(self):
self.elements_added = set()
self.errors = list()
self.errors = []


class _Line(str):
Expand Down Expand Up @@ -650,8 +670,10 @@ class RawConfigParser(MutableMapping):
# Compiled regular expression for matching leading whitespace in a line
NONSPACECRE = re.compile(r"\S")
# Possible boolean values in the configuration.
BOOLEAN_STATES = {'1': True, 'yes': True, 'true': True, 'on': True,
'0': False, 'no': False, 'false': False, 'off': False}
BOOLEAN_STATES: ClassVar[dict[str, bool]] = {
'1': True, 'yes': True, 'true': True, 'on': True,
'0': False, 'no': False, 'false': False, 'off': False,
}

def __init__(self, defaults=None, dict_type=_default_dict,
allow_no_value=False, *, delimiters=('=', ':'),
Expand Down Expand Up @@ -714,11 +736,10 @@ def add_section(self, section):
already exists. Raise ValueError if name is DEFAULT.
"""
if section == self.default_section:
raise ValueError('Invalid section name: %r' % section)
raise ValueError(f'Invalid section name: {section!r}')

if section is UNNAMED_SECTION:
if not self._allow_unnamed_section:
raise UnnamedSectionDisabledError
if section is UNNAMED_SECTION and not self._allow_unnamed_section:
raise UnnamedSectionDisabledError

if section in self._sections:
raise DuplicateSectionError(section)
Expand Down Expand Up @@ -970,13 +991,13 @@ def write(self, fp, space_around_delimiters=True):
preserved when writing the configuration back.
"""
if space_around_delimiters:
d = " {} ".format(self._delimiters[0])
d = f" {self._delimiters[0]} "
else:
d = self._delimiters[0]
if self._defaults:
self._write_section(fp, self.default_section,
self._defaults.items(), d)
if UNNAMED_SECTION in self._sections and self._sections[UNNAMED_SECTION]:
if self._sections.get(UNNAMED_SECTION):
self._write_section(fp, UNNAMED_SECTION, self._sections[UNNAMED_SECTION].items(), d, unnamed=True)

for section in self._sections:
Expand All @@ -988,7 +1009,7 @@ def write(self, fp, space_around_delimiters=True):
def _write_section(self, fp, section_name, section_items, delimiter, unnamed=False):
"""Write a single section to the specified 'fp'."""
if not unnamed:
fp.write("[{}]\n".format(section_name))
fp.write(f"[{section_name}]\n")
for key, value in section_items:
self._validate_key_contents(key)
value = self._interpolation.before_write(self, section_name, key,
Expand All @@ -999,7 +1020,7 @@ def _write_section(self, fp, section_name, section_items, delimiter, unnamed=Fal
.replace('\r', '\n').replace('\n', '\n\t'))
else:
value = ""
fp.write("{}{}\n".format(key, value))
fp.write(f"{key}{value}\n")
fp.write("\n")

def remove_option(self, section, option):
Expand Down Expand Up @@ -1165,7 +1186,7 @@ def _handle_option(self, st, line, fpname):
st.errors.append(ParsingError(fpname, st.lineno, line))
return

st.optname, vi, optval = mo.group('option', 'vi', 'value')
st.optname, optval = mo.group('option', 'value')
if not st.optname:
st.errors.append(ParsingError(fpname, st.lineno, line))
st.optname = self.optionxform(st.optname.rstrip())
Expand Down Expand Up @@ -1225,7 +1246,7 @@ def _convert_to_boolean(self, value):
"""Return a boolean value translating from other types if necessary.
"""
if value.lower() not in self.BOOLEAN_STATES:
raise ValueError('Not a boolean: %s' % value)
raise ValueError(f'Not a boolean: {value}')
return self.BOOLEAN_STATES[value.lower()]

def _validate_key_contents(self, key):
Expand Down Expand Up @@ -1256,9 +1277,8 @@ def _validate_value_types(self, *, section="", option="", value=""):
raise TypeError("section names must be strings or UNNAMED_SECTION")
if not isinstance(option, str):
raise TypeError("option keys must be strings")
if not self._allow_no_value or value:
if not isinstance(value, str):
raise TypeError("option values must be strings")
if (not self._allow_no_value or value) and not isinstance(value, str):
raise TypeError("option values must be strings")

@property
def converters(self):
Expand Down Expand Up @@ -1310,7 +1330,7 @@ def __init__(self, parser, name):
setattr(self, key, getter)

def __repr__(self):
return '<Section: {}>'.format(self._name)
return f'<Section: {self._name}>'

def __getitem__(self, key):
if not self._parser.has_option(self._name, key):
Expand Down Expand Up @@ -1393,8 +1413,7 @@ def __setitem__(self, key, value):
try:
k = 'get' + key
except TypeError:
raise ValueError('Incompatible key: {} (type: {})'
''.format(key, type(key)))
raise ValueError(f'Incompatible key: {key} (type: {type(key)})')
if k == 'get':
raise ValueError('Incompatible key: cannot use "" as a name')
self._data[key] = value
Expand Down
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