# Buggy code
def _merge(self, matches):
    # get matches up to and including first important_match
    #   but if no important_match, then all matches are important_matches
    relevant_matches = self._first_important_matches(matches)

    # get individual lines from important_matches that were marked important
    # these will be prepended to the final result
    def get_marked_lines(match, marker, parameter_obj):
        return (
            tuple(
                line
                for line, flag in zip(
                    match.value(parameter_obj), match.valueflags(parameter_obj)
                )
                if flag is marker
            )
            if match
            else ()
        )

    top_lines = concat(
        get_marked_lines(m, ParameterFlag.top, self) for m in relevant_matches
    )

    # also get lines that were marked as bottom, but reverse the match order so that lines
    # coming earlier will ultimately be last
    bottom_lines = concat(
        get_marked_lines(m, ParameterFlag.bottom, self)
        for m in reversed(relevant_matches)
    )

    # now, concat all lines, while reversing the matches
    #   reverse because elements closer to the end of search path take precedence
    all_lines = concat(m.value(self) for m in reversed(relevant_matches))

    # stack top_lines + all_lines, then de-dupe
    top_deduped = tuple(unique(concatv(top_lines, all_lines)))

    # take the top-deduped lines, reverse them, and concat with reversed bottom_lines
    # this gives us the reverse of the order we want, but almost there
    # NOTE: for a line value marked both top and bottom, the bottom marker will win out
    #       for the top marker to win out, we'd need one additional de-dupe step
    bottom_deduped = unique(
        concatv(reversed(tuple(bottom_lines)), reversed(top_deduped))
    )
    # just reverse, and we're good to go
    return tuple(reversed(tuple(bottom_deduped)))


# Traceback (TypeError)
(test) [hulk@ranganork conda]# conda update conda
Traceback (most recent call last):
File "/root/conda/conda/exceptions.py", line 632, in conda_exception_handler
return_value = func(*args, **kwargs)
File "/root/conda/conda/cli/main.py", line 134, in _main
exit_code = args.func(args, p)
File "/root/conda/conda/cli/main_update.py", line 65, in execute
install(args, parser, 'update')
File "/root/conda/conda/cli/install.py", line 128, in install
context.validate_configuration()
File "/root/conda/conda/common/configuration.py", line 844, in validate_configuration
raise_errors(tuple(chain.from_iterable((errors, post_errors))))
File "/root/conda/conda/common/configuration.py", line 842, in <genexpr>
for name in self.parameter_names)
File "/root/conda/conda/common/configuration.py", line 835, in _collect_validation_error
func(*args, **kwargs)
File "/root/conda/conda/common/configuration.py", line 448, in __get__
result = typify_data_structure(self._merge(matches) if matches else self.default,
File "/root/conda/conda/common/configuration.py", line 596, in _merge
top_deduped = tuple(unique(concatv(top_lines, all_lines)))
File "/root/conda/conda/_vendor/toolz/itertoolz.py", line 209, in unique
for item in seq:
File "/root/conda/conda/common/configuration.py", line 584, in <genexpr>
top_lines = concat(get_marked_lines(m, ParameterFlag.top, self) for m in relevant_matches)
File "/root/conda/conda/common/configuration.py", line 583, in get_marked_lines
if flag is marker) if match else ()
TypeError: zip argument #2 must support iteration

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/conda/envs/test/bin/conda", line 11, in <module>
load_entry_point('conda', 'console_scripts', 'conda')()
File "/root/conda/conda/cli/main.py", line 162, in main
return conda_exception_handler(_main, *args)
File "/root/conda/conda/exceptions.py", line 636, in conda_exception_handler
return handle_exception(e)
File "/root/conda/conda/exceptions.py", line 626, in handle_exception
print_unexpected_error_message(e)
File "/root/conda/conda/exceptions.py", line 588, in print_unexpected_error_message
stderrlogger.info(get_main_info_str(get_info_dict()))
File "/root/conda/conda/cli/main_info.py", line 196, in get_info_dict
channels = list(prioritize_channels(context.channels).keys())
File "/root/conda/conda/base/context.py", line 448, in channels
return self._channels
File "/root/conda/conda/common/configuration.py", line 448, in __get__
result = typify_data_structure(self._merge(matches) if matches else self.default,
File "/root/conda/conda/common/configuration.py", line 596, in _merge
top_deduped = tuple(unique(concatv(top_lines, all_lines)))
File "/root/conda/conda/_vendor/toolz/itertoolz.py", line 209, in unique
for item in seq:
File "/root/conda/conda/common/configuration.py", line 584, in <genexpr>
top_lines = concat(get_marked_lines(m, ParameterFlag.top, self) for m in relevant_matches)
File "/root/conda/conda/common/configuration.py", line 583, in get_marked_lines
if flag is marker) if match else ()
TypeError: zip argument #2 must support iteration

# Fixed code
def _merge(self, matches):
    # get matches up to and including first important_match
    #   but if no important_match, then all matches are important_matches
    relevant_matches_and_values = tuple(
        (match, match.value(self)) for match in self._first_important_matches(matches)
    )
    for match, value in relevant_matches_and_values:
        if not isinstance(value, tuple):
            raise InvalidTypeError(
                self.name,
                value,
                match.source,
                value.__class__.__name__,
                self._type.__name__,
            )

    # get individual lines from important_matches that were marked important
    # these will be prepended to the final result
    def get_marked_lines(match, marker, parameter_obj):
        return (
            tuple(
                line
                for line, flag in zip(
                    match.value(parameter_obj), match.valueflags(parameter_obj)
                )
                if flag is marker
            )
            if match
            else ()
        )

    top_lines = concat(
        get_marked_lines(m, ParameterFlag.top, self)
        for m, _ in relevant_matches_and_values
    )

    # also get lines that were marked as bottom, but reverse the match order so that lines
    # coming earlier will ultimately be last
    bottom_lines = concat(
        get_marked_lines(m, ParameterFlag.bottom, self)
        for m, _ in reversed(relevant_matches_and_values)
    )

    # now, concat all lines, while reversing the matches
    #   reverse because elements closer to the end of search path take precedence
    all_lines = concat(v for _, v in reversed(relevant_matches_and_values))

    # stack top_lines + all_lines, then de-dupe
    top_deduped = tuple(unique(concatv(top_lines, all_lines)))

    # take the top-deduped lines, reverse them, and concat with reversed bottom_lines
    # this gives us the reverse of the order we want, but almost there
    # NOTE: for a line value marked both top and bottom, the bottom marker will win out
    #       for the top marker to win out, we'd need one additional de-dupe step
    bottom_deduped = unique(
        concatv(reversed(tuple(bottom_lines)), reversed(top_deduped))
    )
    # just reverse, and we're good to go
    return tuple(reversed(tuple(bottom_deduped)))