We propose a simple criterion to identify the weak localization (WL) property of graphene in the presence or absence of inter-valley scattering, intrinsic and extrinsic (Rashba) spin-orbit interactions. We show that it is determined by the parity of the number Ns of activated (pseudo-)spins, e.g., sub-lattice, valley and real spins, in the system. If Ns is even (odd), the system shows WL (anti-localization). If a mass term exists, and is not invariant under the relevant time-reversal operation, then unitary behavior (absence of WL correction) is predicted. We discuss some implications of our results to other Dirac fermion systems such as HgTe/HgCdTe quantum well.