<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _prepare_default_dtype(src_array, dtype):
 """Prepare the value of dtype if `dtype` is None. If `src_array` is an NDArray, numpy.ndarray or scipy.sparse.csr.csr_matrix, return src_array.dtype. float32 is returned otherwise."""

    if dtype is None:
        if isinstance(src_array, (NDArray, np.ndarray)):
            dtype = src_array.dtype
        elif spsp and isinstance(src_array, spsp.csr.csr_matrix):
            dtype = src_array.dtype
        else:
            dtype = mx_real_t
    return dtype