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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 detunings_rewrite(expr, combs, omega_laser, symb_omega_levelu, omega_levelu, iu0, ju0):
 r"""Rewrite a symbolic expression in terms of allowed transition detunings. Most times it is possible to express these combinations of optical frequencies in terms of allowed transition detunings. -omega_2 + omega_4 + varpi_1 - varpi_2 '+delta1_2_1-delta2_4_1' But some times it is not possible: -omega_2 + omega_4 - varpi_1 + varpi_2 '300.000000000000-detuning_knob[0]+detuning_knob[1]' """

    Nl = len(omega_laser)
    Neu = len(symb_omega_levelu)
    # We find the coefficients a_i of the field frequencies.
    a = [diff(expr, omega_laser[l]) for l in range(Nl)]

    # We look for a combination of the detunings obtained with the
    # function detunings_code. For each combination we sum the
    # detunings weighed by a_i.
    success = False
    for comb in combs:
        expr_try = 0
        for l in range(Nl):
            expr_try += a[l]*(omega_laser[l] -
                              symb_omega_levelu[comb[l][0]] +
                              symb_omega_levelu[comb[l][1]])
        if expr-expr_try == 0:
            success = True
            break

    assign = ""
    if success:
        for l in range(Nl):
            if a[l] != 0:
                if a[l] == 1:
                    assign += "+"
                elif a[l] == -1:
                    assign += "-"
                assign += "delta"+str(l+1)
                assign += "_"+str(comb[l][0]+1)
                assign += "_"+str(comb[l][1]+1)
    else:
        # We get the code for Hii using detuning knobs.
        # We find out the remainder terms.
        _remainder = expr - sum([a[l]*omega_laser[l]
                                 for l in range(Nl)])
        # We find the coefficients of the remainder.
        b = [diff(_remainder, symb_omega_levelu[j]) for j in range(Neu)]
        # We calculate the remainder numerically.
        remainder = sum([b[j]*omega_levelu[j] for j in range(Neu)])
        # We add the contributions from the detuning knobs.
        remainder += sum([a[l]*(omega_levelu[iu0[l]] -
                                omega_levelu[ju0[l]])
                          for l in range(Nl)])
        assign = str(remainder)
        # We get the code for Hii using detuning knobs.
        for l in range(Nl):
            if a[l] != 0:
                if a[l] == 1:
                    assign += "+"
                elif a[l] == -1:
                    assign += "-"
                assign += "detuning_knob["+str(l)+"]"

    return assign