gh-66449: Add support to unnamed sections in ConfigParser

Lib/configparser.py

@@ -18,7 +18,8 @@
              delimiters=('=', ':'), comment_prefixes=('#', ';'),
              inline_comment_prefixes=None, strict=True,
              empty_lines_in_values=True, default_section='DEFAULT',
-             interpolation=<unset>, converters=<unset>):
+             interpolation=<unset>, converters=<unset>,
+             allow_unnamed_section=False):
 
         Create the parser. When `defaults` is given, it is initialized into the
         dictionary or intrinsic defaults. The keys must be strings, the values
@@ -68,6 +69,12 @@
         converter gets its corresponding get*() method on the parser object and
         section proxies.
 
+        When `allow_unnamed_section` is True (default: False), options
+        without section are accepted: the section for this is
+        ``configparser.UNNAMED_SECTION``. In the file, they are placed before
+        the first explicit section header. This also allows reading and writing
+        files that don't contain any explicit section headers.
+
     sections()
         Return all the configuration section names, sans DEFAULT.
 
@@ -156,7 +163,7 @@
            "ConfigParser", "RawConfigParser",
            "Interpolation", "BasicInterpolation",  "ExtendedInterpolation",
            "LegacyInterpolation", "SectionProxy", "ConverterMapping",
-           "DEFAULTSECT", "MAX_INTERPOLATION_DEPTH")
+           "DEFAULTSECT", "MAX_INTERPOLATION_DEPTH", "TOP_LEVEL")
 
 _default_dict = dict
 DEFAULTSECT = "DEFAULT"
@@ -323,6 +330,20 @@ def __init__(self, filename, lineno, line):
         self.args = (filename, lineno, line)
 
 
+class _UnnamedSection:
+
+    def __repr__(self):
+        return "<TOP_LEVEL>"
+
+    def __eq__(self, other):
+        return repr(self) == repr(other)
+
+    def __hash__(self):
+        return hash(repr(self))
+
+TOP_LEVEL = _UnnamedSection()
+
+
 # Used in parser getters to indicate the default behaviour when a specific
 # option is not found it to raise an exception. Created to enable `None` as
 # a valid fallback value.
@@ -902,7 +923,8 @@ def write(self, fp, space_around_delimiters=True):
 
     def _write_section(self, fp, section_name, section_items, delimiter):
         """Write a single section to the specified `fp`."""
-        fp.write("[{}]\n".format(section_name))
+        if section_name is not TOP_LEVEL:
+            fp.write(f"[{section_name}]\n")
         for key, value in section_items:
             value = self._interpolation.before_write(self, section_name, key,
                                                      value)
@@ -1038,6 +1060,10 @@ def _read(self, fp, fpname):
                 cursect[optname].append(value)
             # a section header or option header?
             else:
+                if self.default_section is TOP_LEVEL and cursect is None:
+                    sectname = TOP_LEVEL
+                    cursect = self._defaults
+
                 indent_level = cur_indent_level
                 # is it a section header?
                 mo = self.SECTCRE.match(value)
@@ -1058,7 +1084,7 @@ def _read(self, fp, fpname):
                         elements_added.add(sectname)
                     # So sections can't start with a continuation line
                     optname = None
-                # no section header in the file?
+                # no section header?
                 elif cursect is None:
                     raise MissingSectionHeaderError(fpname, lineno, line)
                 # an option line?
@@ -1088,6 +1114,7 @@ def _read(self, fp, fpname):
                         # raised at the end of the file and will contain a
                         # list of all bogus lines
                         e = self._handle_error(e, fpname, lineno, line)
+
         self._join_multiline_values()
         # if any parsing errors occurred, raise an exception
         if e:

Lib/test/test_configparser.py

@@ -2119,6 +2119,78 @@ def test_instance_assignment(self):
             self.assertEqual(cfg['two'].getlen('one'), 5)
 
 
+class SectionlessTestCase(unittest.TestCase):
+
+    def fromstring(self, default_section, string):
+        cfg = configparser.ConfigParser(default_section=default_section)
+        cfg.read_string(string)
+        return cfg
+
+    def test_only_top_level(self):
+        cfg1 = self.fromstring(configparser.TOP_LEVEL, """
+        a = 1
+        b = 2
+        """)
+
+        self.assertEqual([], cfg1.sections())
+        self.assertEqual('1', cfg1[configparser.TOP_LEVEL]['a'])
+        self.assertEqual('2', cfg1[configparser.TOP_LEVEL]['b'])
+
+        output = io.StringIO()
+        cfg1.write(output)
+        cfg2 = self.fromstring(configparser.TOP_LEVEL, output.getvalue())
+
+        self.assertEqual([], cfg1.sections())
+        self.assertEqual('1', cfg2[configparser.TOP_LEVEL]['a'])
+        self.assertEqual('2', cfg2[configparser.TOP_LEVEL]['b'])
+
+    def test_only_regular(self):
+        cfg1 = self.fromstring(configparser.TOP_LEVEL, """
+        [sect1]
+        a = 1
+        b = 2
+        """)
+
+        self.assertEqual(['sect1'], cfg1.sections())
+        self.assertEqual('1', cfg1['sect1']['a'])
+        self.assertEqual('2', cfg1['sect1']['b'])
+
+        output = io.StringIO()
+        cfg1.write(output)
+        cfg2 = self.fromstring(configparser.TOP_LEVEL, output.getvalue())
+
+        self.assertEqual(['sect1'], cfg2.sections())
+        self.assertEqual('1', cfg2['sect1']['a'])
+        self.assertEqual('2', cfg2['sect1']['b'])
+
+    def test_top_level_and_regular(self):
+        cfg1 = self.fromstring(configparser.TOP_LEVEL, """
+        a = 1
+        b = 2
+        [sect1]
+        c = 3
+        d = %(a)s%(b)s%(c)s
+        """)
+
+        self.assertEqual(['sect1'], cfg1.sections())
+        self.assertEqual('1', cfg1[configparser.TOP_LEVEL]['a'])
+        self.assertEqual('2', cfg1[configparser.TOP_LEVEL]['b'])
+        self.assertEqual('3', cfg1['sect1']['c'])
+        self.assertEqual('1', cfg1['sect1']['a'])
+        self.assertEqual('123', cfg1['sect1']['d'])
+
+        output = io.StringIO()
+        cfg1.write(output)
+        cfg2 = self.fromstring(configparser.TOP_LEVEL, output.getvalue())
+
+        self.assertEqual(['sect1'], cfg1.sections())
+        self.assertEqual('1', cfg2[configparser.TOP_LEVEL]['a'])
+        self.assertEqual('2', cfg2[configparser.TOP_LEVEL]['b'])
+        self.assertEqual('3', cfg2['sect1']['c'])
+        self.assertEqual('1', cfg2['sect1']['a'])
+        self.assertEqual('123', cfg2['sect1']['d'])
+
+
 class MiscTestCase(unittest.TestCase):
     def test__all__(self):
         support.check__all__(self, configparser, not_exported={"Error"})

Misc/NEWS.d/next/Library/2022-09-22-07-33-00.bpo-22253.jdo4573.rst

@@ -0,0 +1,4 @@
+:class:`configparser.ConfigParser` now accepts unnamed sections before named
+ones, if configured to do so.
+
+Contributed by Pedro Sousa Lacerda and Christian Siefkes.