bokeh serve running but can't access with browser

I have installed bokeh and downloaded myapp.py from the official page (http://docs.bokeh.org/en/latest/docs/user_guide/server.html) which looks like this.

# myapp.py

from random import random

from bokeh.layouts import column
from bokeh.models import Button
from bokeh.palettes import RdYlBu3
from bokeh.plotting import figure, curdoc

# create a plot and style its properties
p = figure(x_range=(0, 100), y_range=(0, 100), toolbar_location=None)
p.border_fill_color = 'black'
p.background_fill_color = 'black'
p.outline_line_color = None
p.grid.grid_line_color = None

# add a text renderer to our plot (no data yet)
r = p.text(x=[], y=[], text=[], text_color=[], text_font_size="20pt",
           text_baseline="middle", text_align="center")

i = 0

ds = r.data_source

# create a callback that will add a number in a random location
def callback():
    global i

    # BEST PRACTICE --- update .data in one step with a new dict
    new_data = dict()
    new_data['x'] = ds.data['x'] + [random()*70 + 15]
    new_data['y'] = ds.data['y'] + [random()*70 + 15]
    new_data['text_color'] = ds.data['text_color'] + [RdYlBu3[i%3]]
    new_data['text'] = ds.data['text'] + [str(i)]
    ds.data = new_data

    i = i + 1

# add a button widget and configure with the call back
button = Button(label="Press Me")
button.on_click(callback)

# put the button and plot in a layout and add to the document
curdoc().add_root(column(button, p))

In the terminal, I then execute:

bokeh serve --show myapp.py

And I see:

2017-04-17 13:24:50,576 Starting Bokeh server version 0.12.5
2017-04-17 13:24:50,581 Starting Bokeh server on port 5006 with applications at paths ['/myapp']
2017-04-17 13:24:50,581 Starting Bokeh server with process id: 700

My browser (tried both Safari and Chrome) then pops open a new tab for http://localhost:5006/myapp but the page doesn't load. It's stuck at about 10% on the progress bar and never changes from "Waiting for localhost...". I have installed the dependencies listed on the bokeh website. What am I missing?

I am running OS X 10.12.4 by the way. I have also tried on a Windows machine and have the exact same problem. There is nothing showing in the console of my web browser, it's just constantly "waiting for 127.0.0.1". I see one "302 GET" request in my terminal if I close the browser and try to reopen the page but that's it.