Add option to specify include_plotlyjs as a path/url to a *.js file

This makes it possible to specify an alternative CDN or offline
location for plotly.js

Author: jonmmease

plotly/offline/offline.py

@@ -449,7 +449,7 @@ def plot(figure_or_data, show_link=True, link_text='Export to plot.ly',
         in a standalone HTML file.
         Use 'div' if you are embedding these graphs in an HTML file with
         other graphs or HTML markup, like a HTML report or an website.
-    include_plotlyjs (True | False | 'cdn' | 'directory' - default=True) --
+    include_plotlyjs (True | False | 'cdn' | 'directory' | path - default=True)
         Specifies how the plotly.js library is included in the output html
         file or div string.
 
@@ -475,6 +475,10 @@ def plot(figure_or_data, show_link=True, link_text='Export to plot.ly',
         the same directory because the plotly.js source code will be included
         only once per output directory, rather than once per output file.
 
+        If a string that ends in '.js', a script tag is included that
+        references the specified path. This approach can be used to point
+        the resulting HTML file to an alternative CDN.
+
         If False, no script tag referencing plotly.js is included. This is
         useful when output_type='div' and the resulting div string will be
         placed inside an HTML document that already loads plotly.js.  This
@@ -530,6 +534,10 @@ def plot(figure_or_data, show_link=True, link_text='Export to plot.ly',
 <script src="https://cdn.plot.ly/plotly-latest.min.js"></script>"""
     elif include_plotlyjs == 'directory':
         plotly_js_script = '<script src="plotly.min.js"></script>'
+    elif (isinstance(include_plotlyjs, six.string_types) and
+          include_plotlyjs.endswith('.js')):
+        plotly_js_script = '<script src="{url}"></script>'.format(
+            url=include_plotlyjs)
     elif include_plotlyjs:
         plotly_js_script = ''.join([
             '<script type="text/javascript">',

plotly/tests/test_core/test_offline/test_offline.py

@@ -183,6 +183,39 @@ def test_including_plotlyjs_directory_div(self):
         # when output_type is div
         self.assertFalse(os.path.exists('plotly.min.js'))
 
+    def test_including_plotlyjs_path_html(self):
+        for include_plotlyjs in [
+            ('https://cdnjs.cloudflare.com/ajax/libs/plotly.js/1.40.1/'
+             'plotly.min.js'),
+                'subpath/to/plotly.min.js',
+                'something.js']:
+
+            html = self._read_html(plotly.offline.plot(
+                fig,
+                include_plotlyjs=include_plotlyjs,
+                output_type='file',
+                auto_open=False))
+            self.assertNotIn(PLOTLYJS, html)
+            self.assertNotIn(cdn_script, html)
+            self.assertNotIn(directory_script, html)
+            self.assertIn(include_plotlyjs, html)
+
+    def test_including_plotlyjs_path_div(self):
+        for include_plotlyjs in [
+            ('https://cdnjs.cloudflare.com/ajax/libs/plotly.js/1.40.1/'
+             'plotly.min.js'),
+                'subpath/to/plotly.min.js',
+                'something.js']:
+
+            html = plotly.offline.plot(
+                fig,
+                include_plotlyjs=include_plotlyjs,
+                output_type='div')
+            self.assertNotIn(PLOTLYJS, html)
+            self.assertNotIn(cdn_script, html)
+            self.assertNotIn(directory_script, html)
+            self.assertIn(include_plotlyjs, html)
+
     def test_div_output(self):
         html = plotly.offline.plot(fig, output_type='div', auto_open=False)