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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 _wl_dist(wl_a, wl_b):
 """Return the distance between two requested wavelengths."""

    if isinstance(wl_a, tuple):
        # central wavelength
        wl_a = wl_a[1]
    if isinstance(wl_b, tuple):
        wl_b = wl_b[1]
    if wl_a is None or wl_b is None:
        return 1000.
    return abs(wl_a - wl_b)