They are not the same set. One is made up by (equivalence classes of) functions with domain $[0,2\pi]$ and the other of functions with domain $[0,2\pi[$. Their elements are different (remember that a function is a triple: domain, codomain, and subset of their cartesian product), and thus they are different sets.
However, they are 'morally' the same vector space: the function $\Psi: L^{p}[0,2\pi] \to L^{p}[0,2\pi[$ that takes $[f]$ to $[f \vert_{[0, 2\pi[}]$ is a linear isomorphism. Surjectivity follows since one can simply extend a function in the codomain to a function in the domain by adding the value $0$ (or any value, really) in $2\pi$.
They are not the same set. One is made up by (equivalence classes of) functions with domain $[0,2\pi]$ and the other of functions with domain $[0,2\pi[$. Their elements are different (remember that a function is a triple: domain, codomain, and subset of their cartesian product), and thus they are different sets. However, they are 'morally' the same vector space: the function $\Psi: L^{p}[0,2\pi] \to L^{p}[0,2\pi[$ that takes $[f]$ to $[f \vert_{[0, 2\pi[}]$ is a linear isomorphism. Surjectivity follows since one can simply extend a function in the codomain to a function in the domain by adding the value $0$ (or any value, really) in $2\pi$.