How to use the pygit2.errors.check_error function in pygit2

def add_push(self, name, refspec):
        """Add a push refspec (str) to the remote
        """

        err = C.git_remote_add_push(self._repo._repo, to_bytes(name), to_bytes(refspec))
        check_error(err)

upstream
            The commit which is considered the upstream.
        """

        if not isinstance(local, Oid):
            local = self.expand_id(local)

        if not isinstance(upstream, Oid):
            upstream = self.expand_id(upstream)

        ahead, behind = ffi.new('size_t*'), ffi.new('size_t*')
        oid1, oid2 = ffi.new('git_oid *'), ffi.new('git_oid *')
        ffi.buffer(oid1)[:] = local.raw[:]
        ffi.buffer(oid2)[:] = upstream.raw[:]
        err = C.git_graph_ahead_behind(ahead, behind, self._repo, oid1, oid2)
        check_error(err)

        return int(ahead[0]), int(behind[0])

path
            The path of the file to look up attributes for, relative to the
            workdir root.

        name
            The name of the attribute to look up.

        flags
            A combination of GIT_ATTR_CHECK_ flags which determine the
            lookup order.
        """

        cvalue = ffi.new('char **')
        err = C.git_attr_get(cvalue, self._repo, flags, to_bytes(path), to_bytes(name))
        check_error(err)

        # Now let's see if we can figure out what the value is
        attr_kind = C.git_attr_value(cvalue[0])
        if attr_kind == C.GIT_ATTR_UNSPECIFIED_T:
            return None
        elif attr_kind == C.GIT_ATTR_TRUE_T:
            return True
        elif attr_kind == C.GIT_ATTR_FALSE_T:
            return False
        elif attr_kind == C.GIT_ATTR_VALUE_T:
            return ffi.string(cvalue[0]).decode('utf-8')

        assert False, "the attribute value from libgit2 is invalid"

def lookup_submodule(self, path):
        csub = ffi.new('git_submodule **')
        cpath = ffi.new('char[]', to_bytes(path))

        err = C.git_submodule_lookup(csub, self._repo, cpath)
        check_error(err)
        return Submodule._from_c(self, csub[0])

Parameters:

        target
            The new target for HEAD. Can be a string or Oid (to detach).
        """

        if isinstance(target, Oid):
            oid = ffi.new('git_oid *')
            ffi.buffer(oid)[:] = target.raw[:]
            err = C.git_repository_set_head_detached(self._repo, oid)
            check_error(err)
            return

        # if it's a string, then it's a reference name
        err = C.git_repository_set_head(self._repo, to_bytes(target))
        check_error(err)

repo = self._repo
        if repo is None:
            raise ValueError('diff needs an associated repository')

        copts = ffi.new('git_diff_options *')
        err = C.git_diff_init_options(copts, 1)
        check_error(err)

        copts.flags = flags
        copts.context_lines = context_lines
        copts.interhunk_lines = interhunk_lines

        cdiff = ffi.new('git_diff **')
        err = C.git_diff_index_to_workdir(cdiff, repo._repo, self._index,
                                          copts)
        check_error(err)

        return Diff.from_c(bytes(ffi.buffer(cdiff)[:]), repo)

if template_path:
        template_path_ref = ffi.new('char []', to_bytes(template_path))
        options.template_path = template_path_ref

    if initial_head:
        initial_head_ref = ffi.new('char []', to_bytes(initial_head))
        options.initial_head = initial_head_ref

    if origin_url:
        origin_url_ref = ffi.new('char []', to_bytes(origin_url))
        options.origin_url = origin_url_ref

    # Call
    crepository = ffi.new('git_repository **')
    err = C.git_repository_init_ext(crepository, to_bytes(path), options)
    check_error(err)

    # Ok
    return Repository(to_str(path))

def save(self):
        """Save a remote to its repository's configuration."""

        err = C.git_remote_save(self._remote)
        check_error(err)

def checkout_head(self, **kwargs):
        """Checkout HEAD

        For arguments, see Repository.checkout().
        """
        copts, refs = Repository._checkout_args_to_options(**kwargs)
        check_error(C.git_checkout_head(self._repo, copts))