Inserting a degree symbol into python plot
Use degree unicode symbol, especially if you don't need LaTeX for other symbols.
U+00B0: °
In python3, it's just: plt.xlabel("Manufactured Ply Angle (°)")
Use LaTeX Style. For Example: $^\circ$ Text
would produce °Text
See the matplotlib documentation for more information about printing (especially mathematical expression).
In your case the code has to be: plt.xlabel('Manufactured Ply Angle $^\circ$')
The TeX part of the expression must be enclosed by dollar signs "$".
Use LaTeX math. On my system the best visual appearance is achieved with
label = r'$45\degree$'
and it looks exactly like the default theta labels of a polar plot.
As others have pointed out kludges like
label = r'$45^\circ$'
label = '$45^o$'
etc. work too but the visual appearance is not so good. On my system these workarounds render a symbol that is slightly too small. YMMV, thus one may want to try what looks best on her system.
For example on a polar contour plot where radius is sine of zenith angle one may want to use
deg_labels = np.array([5, 10, 20, 30, 45, 60, 90])
ax.set_rgrids(np.sin(np.deg2rad(deg_labels)),
labels=(r"${:.0f}\degree$".format(_) for _ in deg_labels))