human
Solve the following python programming problem given the following code:
def _add_tests() : 
    import functools 
    import itertools 
    class Field (object) : 
        @ classmethod 
        def generate_mask(cls) : 
            return list (cls.generate ()) [1] 
class Int1 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 0) 
            (yield 255) 
class Int2 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 0) 
            (yield 4660) 
            (yield 65535) 
class Int3 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 0) 
            (yield 1193046) 
            (yield 16777215) 
class Int4 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 0) 
            (yield 305419896) 
            (yield 4294967295) 
class Int8 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 0) 
            (yield 1311768467463790320) 
            (yield 18446744073709551615) 
class Mac (Field) : 
        @ staticmethod 
        def generate() : 
            (yield '00:00:00:00:00:00') 
            (yield 'f2:0b:a4:7d:f8:ea') 
            (yield 'ff:ff:ff:ff:ff:ff') 
class IPv4 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield '0.0.0.0') 
            (yield '192.0.2.1') 
            (yield '255.255.255.255') 
class IPv6 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield '::') 
            (yield 'fe80::f00b:a4ff:fed0:3f70') 
            (yield 'ffff:ffff:ffff:ffff:ffff:ffff:ffff:ffff') 
class B64 (Field) : 
        @ staticmethod 
        def generate() : 
            (yield 'aG9nZWhvZ2U=') 
            (yield 'ZnVnYWZ1Z2E=') 
ofpps = [ofproto_v1_2_parser, ofproto_v1_3_parser, ofproto_v1_4_parser, ofproto_v1_5_parser] 
    common = [('in_port', Int4), ('in_phy_port', Int4), ('metadata', Int8), ('eth_dst', Mac), ('eth_src', Mac), ('eth_type', Int2), ('vlan_vid', Int2), ('vlan_pcp', Int1), ('ip_dscp', Int1), ('ip_ecn', Int1), ('ip_proto', Int1), ('ipv4_src', IPv4), ('ipv4_dst', IPv4),...

    
    

    Fix the buggy line: for C in itertools.combinations (L [values], n) :
assistant
#Here is Python code to fix the buggy line: for C in itertools.

for C in itertools.combinations (L [ofpp], n) :