How to use the rosdep.core function in rosdep

def assert_file_hash(filename, md5sum):
    md5 = hashlib.md5()
    with open(filename,'rb') as f: 
        for chunk in iter(lambda: f.read(8192), ''): 
            md5.update(chunk)
    if md5sum != md5.hexdigest():
        raise rosdep.core.RosdepException("md5sum check on %s failed.  Expected %s got %s"%(filename, md5sum, md5.hexdigest()))

except yaml.scanner.ScannerError as ex:
            raise rosdep.core.RosdepException("Failed to parse yaml in %s:  Error: %s"%(contents, ex))
                
        if "ROSDEP_DEBUG" in os.environ:
            print "Downloaded manifest:\n{{{%s\n}}}\n"%self.manifest
        
        self.install_command = self.manifest.get("install-script", "#!/bin/bash\n#no install-script specificd")
        self.check_presence_command = self.manifest.get("check-presence-script", "#!/bin/bash\n#no check-presence-script\nfalse")

        self.exec_path = self.manifest.get("exec-path", ".")

        self.depends = self.manifest.get("depends", [])

        self.tarball = self.manifest.get("uri")
        if not self.tarball:
            raise rosdep.core.RosdepException("uri required for source rosdeps") 
        self.alternate_tarball = self.manifest.get("alternate-uri")
        self.tarball_md5sum = self.manifest.get("md5sum")

def get_installer(self, mode):
        """ 
        Return the correct installer for a given OS from the
        self.installer dict.
        """
        try:
            if not mode in self.installers:
                raise rosdep.core.RosdepException("Invalid installation mode %s for %s"%(mode, self.get_name()))
            return self.installers[mode]
        except NameError as ex:
            raise rosdep.core.RosdepException("Invalid installation mode %s for %s"%(mode, self.get_name()))

def get_installer(self, mode):
        """ 
        Return the correct installer for a given OS from the
        self.installer dict.
        """
        try:
            if not mode in self.installers:
                raise rosdep.core.RosdepException("Invalid installation mode %s for %s"%(mode, self.get_name()))
            return self.installers[mode]
        except NameError as ex:
            raise rosdep.core.RosdepException("Invalid installation mode %s for %s"%(mode, self.get_name()))

missing_packages = r.satisfy()
            if not missing_packages:
                return 0
            else:
                print("The following rosdeps are not installed but are required", missing_packages)
                return 1
        
        elif command == "install":
            error = r.install(options.include_duplicates, options.default_yes)
            if error:
                print("rosdep install ERROR:\n%s"%error, file=sys.stderr)
                return 1
            else:
                print("All required rosdeps installed successfully")
                return 0
    except core.RosdepException as e:
        print("ERROR: %s"%e, file=sys.stderr)
        return 1

    try:
        if command == "depdb":
            print(r.depdb(verified_packages))
            return 0

        elif command == "what_needs":
            print('\n'.join(r.what_needs(rdargs)))
            return 0

        elif command == "where_defined":
            print(r.where_defined(rdargs))
            return 0