<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def store(self):
 """ Store and return packages for upgrading """

        data = repo_data(self.PACKAGES_TXT, "slack", self.flag)
        black = BlackList().packages(pkgs=data[0], repo="slack")
        for name, loc, comp, uncomp in zip(data[0], data[1], data[2], data[3]):
            status(0.0003)
            repo_pkg_name = split_package(name)[0]
            if (not os.path.isfile(self.meta.pkg_path + name[:-4]) and
                    repo_pkg_name not in black and
                    repo_pkg_name not in self.skip):
                self.dwn_links.append("{0}{1}/{2}".format(mirrors("", ""),
                                                          loc, name))
                self.comp_sum.append(comp)
                self.uncomp_sum.append(uncomp)
                self.upgrade_all.append(name)
                self.count_upg += 1
                if not find_package(repo_pkg_name + self.meta.sp,
                                    self.meta.pkg_path):
                    self.count_added += 1
                    self.count_upg -= 1
        return self.count_upg