configparser: whitespace not stripped when writing empty values

Bug description:

When writing a configparser.ConfigParser to a file, keys with an empty value add a whitespace at the end of the line.

Eg. a line key = , ending with a whitespace.

import configparser
config = configparser.ConfigParser()
config["DEFAULT"] = {'ok': 'value', 'error': ''}
with open("test.ini", "w") as fhandle:
    config.write(fhandle)

Now the contents of test.ini are:

[DEFAULT]
ok = value
error = 

The line with the key "error" ends in a space. It appears the extra whitespace is introduced in ConfigParser.write(). Whitespaces are added to the delimiter, but this does not account for empty values.

class ConfigParser:
    def write(self, fp, space_around_delimiters=True):
        if space_around_delimiters:
            d = " {} ".format(self._delimiters[0])
        ...

Stripping the whitespace of the value in ConfigParser._write_section() solves this.

class ConfigParser:
    def _write_section(self, fp, section_name, section_items, delimiter, unnamed=False):
        if not unnamed:
            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, value
            )
            if value is not None or not self._allow_no_value:
                # Convert all possible line-endings into '\n\t'
                value = (delimiter + str(value).replace('\r\n', '\n')
                         .replace('\r', '\n').replace('\n', '\n\t'))
            else:
                value = ""
            # Change from the original: strip empty space to avoid "key = " for
            # empty keys!!!
            line = f"{key}{value}".strip(" ")
            fp.write(f"{line}\n")
            # Done with changes.
        fp.write("\n")

CPython versions tested on:

3.14

Operating systems tested on:

Linux

Linked PRs

• gh-157467

Start at ConfigParser.write() and _write_section(), which the issue identifies as the entry points introducing the trailing space. Add coverage for writing an empty value and verify the generated INI line has no trailing whitespace, then run the relevant configparser tests. A linked PR is already noted on the issue.