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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def pauli_from_char(ch, n=0):
 """Make Pauli matrix from an character. Args: ch (str):
 "X" or "Y" or "Z" or "I". n (int, optional):
 Make Pauli matrix as n-th qubits. Returns: If ch is "X" => X, "Y" => Y, "Z" => Z, "I" => I Raises: ValueError: When ch is not "X", "Y", "Z" nor "I". """

    ch = ch.upper()
    if ch == "I":
        return I
    if ch == "X":
        return X(n)
    if ch == "Y":
        return Y(n)
    if ch == "Z":
        return Z(n)
    raise ValueError("ch shall be X, Y, Z or I")