DeprecationWarning: invalid escape sequence

There are many warnings that can be simply solved by adding an r before the strings containing Latex code. For example ax.set_xlabel(r"$\kappa_h$") instead of ax.set_xlabel("$\kappa_h$").

@jreneuve can you please do that (in a specific topic)?

/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spectra.py:245: DeprecationWarning: invalid escape sequence \k
  ax.set_xlabel("$\kappa_h$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:154: DeprecationWarning: invalid escape sequence \P
  ylbl = "$\Pi(" + xlbl + ")/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:154: DeprecationWarning: invalid escape sequence \e
  ylbl = "$\Pi(" + xlbl + ")/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:163: DeprecationWarning: invalid escape sequence \P
  k_plot, flux_tot / eps, "k", linewidth=2, label="$\Pi/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:165: DeprecationWarning: invalid escape sequence \e
  ax.semilogx(k_plot, D / eps, "k--", linewidth=2, label="$D/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:167: DeprecationWarning: invalid escape sequence \P
  k_plot, (flux_tot + D) / eps, "k:", label="$(\Pi+D)/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:169: DeprecationWarning: invalid escape sequence \P
  ax.semilogx(k_plot, flux_K / eps, "r", label="$\Pi_K/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:170: DeprecationWarning: invalid escape sequence \P
  ax.semilogx(k_plot, flux_A / eps, "b", label="$\Pi_A/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:171: DeprecationWarning: invalid escape sequence \e
  ax.semilogx(k_plot, DK / eps, "r--", label="$D_K/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:172: DeprecationWarning: invalid escape sequence \e
  ax.semilogx(k_plot, DA / eps, "b--", label="$D_A/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/strat/output/spect_energy_budget.py:173: DeprecationWarning: invalid escape sequence \e
  ax.semilogx(k_plot, CK2A / eps, "m", linewidth=2, label="$B/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:262: DeprecationWarning: invalid escape sequence \k
  ax.set_xlabel("$\kappa_h$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:336: DeprecationWarning: invalid escape sequence \P
  ylbl = "$\Pi(" + xlbl + ")/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:336: DeprecationWarning: invalid escape sequence \e
  ylbl = "$\Pi(" + xlbl + ")/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:345: DeprecationWarning: invalid escape sequence \P
  k_plot, flux_tot / eps, "k", linewidth=2, label="$\Pi/\epsilon$"
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:347: DeprecationWarning: invalid escape sequence \e
  ax.semilogx(k_plot, D / eps, "k--", linewidth=2, label="$D/\epsilon$")
/builds/fluiddyn/fluidsim/fluidsim/solvers/ns3d/output/spect_energy_budget.py:349: DeprecationWarning: invalid escape sequence \P
  k_plot, (flux_tot + D) / eps, "k:", label="$(\Pi+D)/\epsilon$"