pythongh-107625: Raise ParsingError if a key contains empty value

- raise ParsingError instaed of AttributeError if a key
  contains empty value in a non recommended scenario where
  extra space and blankline is present within the section

Doc/library/configparser.rst

@@ -1036,6 +1036,12 @@ ConfigParser Objects
       files using :meth:`read_file` before calling :meth:`read` for any
       optional files::
 
+      Raise a :exc:`ParsingError` instead of an :exc:`AttributeError`
+      when the configuration contains a key without a corresponding value.
+      This change is intended to handle scenarios where a key lacks a value
+      in a configuration. Please note that it's not recommended to have extra
+      spaces or blank lines within sections of the configuration.
+
          import configparser, os
 
          config = configparser.ConfigParser()
@@ -1053,6 +1059,12 @@ ConfigParser Objects
       .. versionadded:: 3.7
          The *filenames* parameter accepts a :class:`bytes` object.
 
+     .. versionchanged:: 3.13
+        Parsing errors will result in a ParsingError being raised instead
+        of an AttributeError when encountering a key without a corresponding
+        value. This change is designed to handle situations where a key is
+        present without a value, particularly in scenarios not recommended,
+        such as having extra spaces or blank lines within sections.
 
    .. method:: read_file(f, source=None)
 
@@ -1063,9 +1075,23 @@ ConfigParser Objects
       not given and *f* has a :attr:`name` attribute, that is used for
       *source*; the default is ``'<???>'``.
 
+      Raise a :exc:`ParsingError` instead of an :exc:`AttributeError`
+      when the configuration contains a key without a corresponding value.
+      This change is intended to handle scenarios where a key lacks a value
+      in a configuration. Please note that it's not recommended to have extra
+      spaces or blank lines within sections of the configuration.
+
       .. versionadded:: 3.2
          Replaces :meth:`readfp`.
 
+     .. versionchanged:: 3.13
+        Parsing errors will result in a ParsingError being raised instead
+        of an AttributeError when encountering a key without a corresponding
+        value. This change is designed to handle situations where a key is
+        present without a value, particularly in scenarios not recommended,
+        such as having extra spaces or blank lines within sections.
+
+
    .. method:: read_string(string, source='<string>')
 
       Parse configuration data from a string.

Lib/configparser.py

@@ -986,8 +986,11 @@ def _read(self, fp, fpname):
             first_nonspace = self.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(value)
+               cur_indent_level > indent_level):
+               if cursect[optname]:
+                   cursect[optname].append(value)
+               else:
+                   raise ParsingError(f"No-value option {optname} cannot be continued")
             # a section header or option header?
             else:
                 indent_level = cur_indent_level

Lib/test/test_configparser.py

@@ -1555,6 +1555,22 @@ def test_source_as_bytes(self):
             "'[badbad'"
         )
 
+    def test_gh_107625(self):
+       #test key without value with extra whitespace within sections
+       lines = [
+           '[SECT]\n',
+           'KEY1\n',
+           ' KEY2 = VAL2\n', # note the Space before the key!
+           ]
+       with self.assertRaises(configparser.ParsingError):
+           parser = configparser.ConfigParser(
+               comment_prefixes ="",
+               allow_no_value   =True,
+               strict           =False,
+               delimiters       =( '=', ),
+               interpolation    =None,
+           )
+
 
 class CoverageOneHundredTestCase(unittest.TestCase):
     """Covers edge cases in the codebase."""