How to use the pbr.git._run_git_command function in pbr

def _get_version_from_git(pre_version):
    """Return a version which is equal to the tag that's on the current
    revision if there is one, or tag plus number of additional revisions
    if the current revision has no tag.
    """

    git_dir = git._run_git_functions()
    if git_dir:
        if pre_version:
            try:
                return git._run_git_command(
                    ['describe', '--exact-match'], git_dir,
                    throw_on_error=True).replace('-', '.')
            except Exception:
                return "%s.dev%s" % (pre_version, _get_revno(git_dir))
        else:
            # git describe always is going to return one of three things
            # - a short-sha if there are no tags
            # - a tag, if there's one on the current revision
            # - a string of the form $last_tag-$revs_since_last_tag-g$short_sha
            raw_version = git._run_git_command(['describe', '--always'],
                                               git_dir)
            # First, if there are no -'s or .'s, then it's just a short sha.
            # Create a synthetic version for it.
            if '-' not in raw_version and '.' not in raw_version:
                return "0.0.0.post%s" % _get_revno(git_dir)
            # Now, we want to strip the short-sha prefix

def _get_increment_kwargs(git_dir, tag):
    """Calculate the sort of semver increment needed from git history.

    Every commit from HEAD to tag is consider for Sem-Ver metadata lines.
    See the pbr docs for their syntax.

    :return: a dict of kwargs for passing into SemanticVersion.increment.
    """
    result = {}
    if tag:
        version_spec = tag + "..HEAD"
    else:
        version_spec = "HEAD"
    changelog = git._run_git_command(['log', version_spec], git_dir)
    header_len = len('    sem-ver:')
    commands = [line[header_len:].strip() for line in changelog.split('\n')
                if line.lower().startswith('    sem-ver:')]
    symbols = set()
    for command in commands:
        symbols.update([symbol.strip() for symbol in command.split(',')])

    def _handle_symbol(symbol, symbols, impact):
        if symbol in symbols:
            result[impact] = True
            symbols.discard(symbol)
    _handle_symbol('bugfix', symbols, 'patch')
    _handle_symbol('feature', symbols, 'minor')
    _handle_symbol('deprecation', symbols, 'minor')
    _handle_symbol('api-break', symbols, 'major')
    for symbol in symbols:

"""Calculate the sort of semver increment needed from git history.

    Every commit from HEAD to tag is consider for Sem-Ver metadata lines.
    See the pbr docs for their syntax.

    :return: a dict of kwargs for passing into SemanticVersion.increment.
    """
    result = {}
    if tag:
        version_spec = tag + "..HEAD"
    else:
        version_spec = "HEAD"
    # Get the raw body of the commit messages so that we don't have to
    # parse out any formatting whitespace and to avoid user settings on
    # git log output affecting out ability to have working sem ver headers.
    changelog = git._run_git_command(['log', '--pretty=%B', version_spec],
                                     git_dir)
    header_len = len('sem-ver:')
    commands = [line[header_len:].strip() for line in changelog.split('\n')
                if line.lower().startswith('sem-ver:')]
    symbols = set()
    for command in commands:
        symbols.update([symbol.strip() for symbol in command.split(',')])

    def _handle_symbol(symbol, symbols, impact):
        if symbol in symbols:
            result[impact] = True
            symbols.discard(symbol)
    _handle_symbol('bugfix', symbols, 'patch')
    _handle_symbol('feature', symbols, 'minor')
    _handle_symbol('deprecation', symbols, 'minor')
    _handle_symbol('api-break', symbols, 'major')

def _get_version_from_git(pre_version=None):
    """Calculate a version string from git.

    If the revision is tagged, return that. Otherwise calculate a semantic
    version description of the tree.

    The number of revisions since the last tag is included in the dev counter
    in the version for untagged versions.

    :param pre_version: If supplied use this as the target version rather than
        inferring one from the last tag + commit messages.
    """
    git_dir = git._run_git_functions()
    if git_dir:
        try:
            tagged = git._run_git_command(
                ['describe', '--exact-match'], git_dir,
                throw_on_error=True).replace('-', '.')
            target_version = version.SemanticVersion.from_pip_string(tagged)
        except Exception:
            if pre_version:
                # not released yet - use pre_version as the target
                target_version = version.SemanticVersion.from_pip_string(
                    pre_version)
            else:
                # not released yet - just calculate from git history
                target_version = None
        result = _get_version_from_git_target(git_dir, target_version)
        return result.release_string()
    # If we don't know the version, return an empty string so at least
    # the downstream users of the value always have the same type of
    # object to work with.

def _get_version_from_git(pre_version=None):
    """Calculate a version string from git.

    If the revision is tagged, return that. Otherwise calculate a semantic
    version description of the tree.

    The number of revisions since the last tag is included in the dev counter
    in the version for untagged versions.

    :param pre_version: If supplied use this as the target version rather than
        inferring one from the last tag + commit messages.
    """
    git_dir = git._run_git_functions()
    if git_dir:
        try:
            tagged = git._run_git_command(
                ['describe', '--exact-match'], git_dir,
                throw_on_error=True).replace('-', '.')
            target_version = version.SemanticVersion.from_pip_string(tagged)
        except Exception:
            if pre_version:
                # not released yet - use pre_version as the target
                target_version = version.SemanticVersion.from_pip_string(
                    pre_version)
            else:
                # not released yet - just calculate from git history
                target_version = None
        result = _get_version_from_git_target(git_dir, target_version)
        return result.release_string()
    # If we don't know the version, return an empty string so at least
    # the downstream users of the value always have the same type of
    # object to work with.

def _get_increment_kwargs(git_dir, tag):
    """Calculate the sort of semver increment needed from git history.

    Every commit from HEAD to tag is consider for Sem-Ver metadata lines.
    See the pbr docs for their syntax.

    :return: a dict of kwargs for passing into SemanticVersion.increment.
    """
    result = {}
    if tag:
        version_spec = tag + "..HEAD"
    else:
        version_spec = "HEAD"
    changelog = git._run_git_command(['log', version_spec], git_dir)
    header_len = len('    sem-ver:')
    commands = [line[header_len:].strip() for line in changelog.split('\n')
                if line.lower().startswith('    sem-ver:')]
    symbols = set()
    for command in commands:
        symbols.update([symbol.strip() for symbol in command.split(',')])

    def _handle_symbol(symbol, symbols, impact):
        if symbol in symbols:
            result[impact] = True
            symbols.discard(symbol)
    _handle_symbol('bugfix', symbols, 'patch')
    _handle_symbol('feature', symbols, 'minor')
    _handle_symbol('deprecation', symbols, 'minor')
    _handle_symbol('api-break', symbols, 'major')
    for symbol in symbols: