... [first-section]

    ...

    ... variable=${mako_variable}

    ... variable2  =\tvalue after tab

    ... ## This section had some whitespace and stuff

    ...

    ...

    ... # ${mako_function()}

    ... [second-section]

    ... %if conditional_options == 'option-a':

    ... # option a was chosen

    ... %elif conditional_options == 'option-b':

    ... some_variable = "never mind - option-b will not be used anyway ..."

    ... %endif

    ...

    ... [comment-section]

    ... #variable3 = 3.0

    ... #variable4 = 4.0

    ... #variable5 = 5.0

    ... variable5 = 5.1

    ... #variable6 = 6.0

    ... #variable6 = 6.1

    ... #variable7 = 7.0

    ... variable7 = 7.1

    ... '''

    >>> mako_variable_values = {'mako_variable': 'VALUE', 'mako_function': (lambda: 'FUNCTION RESULT'),

    ...                         'conditional_options': 'option-a', 'http_server': 'nc'}

    >>> settings = { # only partially used

    ...     '[third-section]': {'third_extra': ' 3'},

    ...     '[fourth-section]': {'fourth_extra': '4', 'fourth': '"four"'},

    ... }

    >>> print(expand(template, mako_variable_values, settings))

    ERROR: http_server is 'nc' - it should be one of 'waitress', 'gearbox', 'gevent', 'gunicorn', 'uwsgi'

    <BLANKLINE>

    [first-section]

    <BLANKLINE>

    variable=VALUE

    #variable2  =    value after tab

    variable2 = VAL2

    <BLANKLINE>

    first_extra = EXTRA

    <BLANKLINE>

    <BLANKLINE>

    # FUNCTION RESULT

    [second-section]

    # option a was chosen

    <BLANKLINE>

    [comment-section]

    variable3 = 3.0

    #variable4 = 4.0

    variable4 = 4.1

    #variable5 = 5.0

    #variable5 = 5.1

    variable5 = 5.2

    #variable6 = 6.0

    #variable6 = 6.1

    variable6 = 6.2

    variable7 = 7.0

    #variable7 = 7.1

    <BLANKLINE>

    [fourth-section]

    fourth = "four"

    fourth_extra = 4

    <BLANKLINE>

    [third-section]

    third_extra =  3

    <BLANKLINE>

    """

    mako_variables = dict(default_variables)

    mako_variables.update(mako_variable_values or {})

    settings = dict((k, dict(v)) for k, v in settings.items()) # deep copy before mutating

    for key, value in mako_variables.items():

        if key in variable_options:

            if value not in variable_options[key]:

                print('ERROR: %s is %r - it should be one of %s' %

                      (key, value, ', '.join(repr(x) for x in variable_options[key])))

    ini_lines = mako.template.Template(template).render(**mako_variables)

    def process_section(m):

        """process a ini section, replacing values as necessary"""

        sectionname, lines = m.groups()

        if sectionname in settings:

            section_settings = settings.pop(sectionname)

            add_after_key_value = {}  # map key to value it should be added after

            # 1st pass:

            # comment out lines with keys that have new values

            # find best line for keeping or un-commenting (because it has the right value) or adding after (because it is the last with other value)

            def comment_out(m):

                """process a section line if in section_settings and comment out and track in add_after_key_value"""

                line = m.group(0)

                comment, key, line_value = m.groups()

                if key not in section_settings:

                    return line

                new_value = section_settings[key]

                if line_value == new_value or add_after_key_value.get(key) != new_value:

                    add_after_key_value[key] = line_value

                if comment:

                    return line

                return '#' + line

            lines = re.sub(r'^(#)?([^#\n\s]*)[ \t]*=[ \t]*(.*)$', comment_out, lines, flags=re.MULTILINE)

            def add_after_comment(m):

                """process a section comment line and add new value"""

                line = m.group(0)

                key, line_value = m.groups()

                if key not in section_settings:

                    return line

                if line_value != add_after_key_value.get(key):

                    return line

                new_value = section_settings[key]

                if new_value == line_value:

                    line = line.lstrip('#')

                else:

                    line += '\n%s = %s' % (key, new_value)

                section_settings.pop(key)

                return line

            lines = re.sub(r'^#([^#\n\s]*)[ \t]*=[ \t]*(.*)$', add_after_comment, lines, flags=re.MULTILINE)

            if section_settings:

                lines += '\n' + ''.join('%s = %s\n' % (key, value) for key, value in sorted(section_settings.items()))

        return sectionname + '\n' + lines

    # process sections until comments before next section or end

    ini_lines = re.sub(r'''^

        (\[.*\])\n

        # after the section name, a number of chunks with:

        (

            (?:

                # a number of comments or empty lines

                (?:[#].*\n|\n)*

                # one or more non-empty non-comments non-section-start lines

                (?:[^\n#[].*\n)+

                # a number of comments - not empty lines

                (?:[#].*\n)*

            )*

        )

        ''',

        process_section, ini_lines, flags=re.MULTILINE | re.VERBOSE) \

        + \

        ''.join(

            '\n' + sectionname + '\n' + ''.join('%s = %s\n' % (key, value) for key, value in sorted(section_settings.items()))