Print string over plotted line (mimic contour plot labels)

Question

The contour plot demo shows how you can plot the curves with the level value plotted over them, see below.

Answer 1

Based on Jakob's code, here is a function that rotates the text in data space, puts labels near a given x or y data coordinate, and works also with log plots.

def label_line(line, label_text, near_i=None, near_x=None, near_y=None, rotation_offset=0, offset=(0,0)):
    """call 
        l, = plt.loglog(x, y)
        label_line(l, "text", near_x=0.32)
    """
    def put_label(i):
        """put label at given index"""
        i = min(i, len(x)-2)
        dx = sx[i+1] - sx[i]
        dy = sy[i+1] - sy[i]
        rotation = np.rad2deg(math.atan2(dy, dx)) + rotation_offset
        pos = [(x[i] + x[i+1])/2. + offset[0], (y[i] + y[i+1])/2 + offset[1]]
        plt.text(pos[0], pos[1], label_text, size=9, rotation=rotation, color = line.get_color(),
        ha="center", va="center", bbox = dict(ec='1',fc='1'))

    x = line.get_xdata()
    y = line.get_ydata()
    ax = line.get_axes()
    if ax.get_xscale() == 'log':
        sx = np.log10(x)    # screen space
    else:
        sx = x
    if ax.get_yscale() == 'log':
        sy = np.log10(y)
    else:
        sy = y

    # find index
    if near_i is not None:
        i = near_i
        if i < 0: # sanitize negative i
            i = len(x) + i
        put_label(i)
    elif near_x is not None:
        for i in range(len(x)-2):
            if (x[i] < near_x and x[i+1] >= near_x) or (x[i+1] < near_x and x[i] >= near_x):
                put_label(i)
    elif near_y is not None:
        for i in range(len(y)-2):
            if (y[i] < near_y and y[i+1] >= near_y) or (y[i+1] < near_y and y[i] >= near_y):
                put_label(i)
    else:
        raise ValueError("Need one of near_i, near_x, near_y")