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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 get_lt(hdr):
 """Obtain the LTV and LTM keyword values. Note that this returns the values just as read from the header, which means in particular that the LTV values are for one-indexed pixel coordinates. LTM keywords are the diagonal elements of MWCS linear transformation matrix, while LTV's are MWCS linear transformation vector (1-indexed). .. note:: Translated from ``calacs/lib/getlt.c``. Parameters hdr : obj Extension header. Returns ------- ltm, ltv : tuple of float ``(LTM1_1, LTM2_2)`` and ``(LTV1, LTV2)``. Values are ``(1, 1)`` and ``(0, 0)`` if not found, to accomodate reference files with missing info. Raises ------ ValueError Invalid LTM* values. """

    ltm = (hdr.get('LTM1_1', 1.0), hdr.get('LTM2_2', 1.0))

    if ltm[0] <= 0 or ltm[1] <= 0:
        raise ValueError('(LTM1_1, LTM2_2) = {0} is invalid'.format(ltm))

    ltv = (hdr.get('LTV1', 0.0), hdr.get('LTV2', 0.0))
    return ltm, ltv