How to use the zulip.integrations.perforce.git_p4.CalledProcessError function in zulip

def system(cmd):
    expand = isinstance(cmd, six.string_types)
    if verbose:
        sys.stderr.write("executing %s\n" % str(cmd))
    retcode = subprocess.call(cmd, shell=expand)
    if retcode:
        raise CalledProcessError(retcode, cmd)

if not self.cloneDestination:
            self.cloneDestination = self.defaultDestination(args)

        print("Importing from %s into %s" % (', '.join(depotPaths), self.cloneDestination))

        if not os.path.exists(self.cloneDestination):
            os.makedirs(self.cloneDestination)
        chdir(self.cloneDestination)

        init_cmd = [ "git", "init" ]
        if self.cloneBare:
            init_cmd.append("--bare")
        retcode = subprocess.call(init_cmd)
        if retcode:
            raise CalledProcessError(retcode, init_cmd)

        if not P4Sync.run(self, depotPaths):
            return False

        # create a master branch and check out a work tree
        if gitBranchExists(self.branch):
            system([ "git", "branch", "master", self.branch ])
            if not self.cloneBare:
                system([ "git", "checkout", "-f" ])
        else:
            print('Not checking out any branch, use ' \
                  '"git checkout -q -b master "')

        # auto-set this variable if invoked with --use-client-spec
        if self.useClientSpec_from_options:
            system("git config --bool git-p4.useclientspec true")

def p4_system(cmd):
    """Specifically invoke p4 as the system command. """
    real_cmd = p4_build_cmd(cmd)
    expand = isinstance(real_cmd, six.string_types)
    retcode = subprocess.call(real_cmd, shell=expand)
    if retcode:
        raise CalledProcessError(retcode, real_cmd)