ENH: use altair_saver for image export

.github/workflows/build.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        python-version: [ '3.5', '3.6', '3.7', '3.8' ]
+        python-version: [ '3.6', '3.7', '3.8' ]
     name: Python ${{ matrix.python-version }}
     steps:
     - uses: actions/checkout@v1
@@ -24,7 +24,7 @@ jobs:
       run: |
         python -m pip install --upgrade pip
         pip install .[dev]
-        pip install selenium
+        pip install altair_saver
     - name: Test with pytest
       run: |
         pytest --doctest-modules altair

altair/sphinxext/altairgallery.py

@@ -132,7 +132,7 @@ def save_example_pngs(examples, image_dir, make_thumbnails=True):
                 chart.save(image_file)
                 hashes[filename] = example_hash
             except ImportError:
-                warnings.warn("Could not import selenium: using generic image")
+                warnings.warn("Unable to save image: using generic image")
                 create_generic_image(image_file)
 
             with open(hash_file, 'w') as f:

altair/utils/mimebundle.py

@@ -1,6 +1,3 @@
-import base64
-
-from .headless import compile_spec
 from .html import spec_to_html
 
 
@@ -12,13 +9,13 @@ def spec_to_mimebundle(spec, format, mode=None,
     """Convert a vega/vega-lite specification to a mimebundle
 
     The mimebundle type is controlled by the ``format`` argument, which can be
-    one of the following ['png', 'svg', 'vega', 'vega-lite', 'html', 'json']
+    one of the following ['html', 'json', 'png', 'svg', 'pdf', 'vega', 'vega-lite']
 
     Parameters
     ----------
     spec : dict
         a dictionary representing a vega-lite plot spec
-    format : string {'png', 'svg', 'vega', 'vega-lite', 'html', 'json'}
+    format : string {'html', 'json', 'png', 'svg', 'pdf', 'vega', 'vega-lite'}
         the file format to be saved.
     mode : string {'vega', 'vega-lite'}
         The rendering mode.
@@ -38,9 +35,8 @@ def spec_to_mimebundle(spec, format, mode=None,
 
     Note
     ----
-    The png, svg, and vega outputs require the pillow and selenium Python modules
-    to be installed. Additionally they requires either chromedriver
-    (if webdriver=='chrome') or geckodriver (if webdriver=='firefox')
+    The png, svg, pdf, and vega outputs require the altair_saver package
+    to be installed.
     """
     if mode not in ['vega', 'vega-lite']:
         raise ValueError("mode must be either 'vega' or 'vega-lite'")
@@ -49,34 +45,29 @@ def spec_to_mimebundle(spec, format, mode=None,
         if vega_version is None:
             raise ValueError("Must specify vega_version")
         return {'application/vnd.vega.v{}+json'.format(vega_version[0]): spec}
-    elif format in ['png', 'svg', 'vega']:
-        render = compile_spec(spec, format=format, mode=mode,
-                              vega_version=vega_version,
-                              vegaembed_version=vegaembed_version,
-                              vegalite_version=vegalite_version, **kwargs)
-        if format == 'png':
-            render = base64.b64decode(render.split(',', 1)[1].encode())
-            return {'image/png': render}
-        elif format == 'svg':
-            return {'image/svg+xml': render}
-        elif format == 'vega':
-            assert mode == 'vega-lite'  # TODO: handle vega->vega conversion more gracefully
-            return {'application/vnd.vega.v{}+json'.format(vega_version[0]): render}
-    elif format == 'html':
+    if format in ['png', 'svg', 'pdf', 'vega']:
+        try:
+            import altair_saver
+        except ImportError:
+            raise ValueError(
+                "Saving charts in {fmt!r} format requires the altair_saver package: "
+                "see http://github.com/altair-viz/altair_saver/".format(fmt=format)
+            )
+        return altair_saver.render(spec, format, mode=mode, **kwargs)
+    if format == 'html':
         html = spec_to_html(spec, mode=mode,
                             vega_version=vega_version,
                             vegaembed_version=vegaembed_version,
                             vegalite_version=vegalite_version, **kwargs)
         return {'text/html': html}
-    elif format == 'vega-lite':
+    if format == 'vega-lite':
         assert mode == 'vega-lite'  # sanity check: should never be False
         if mode == 'vega':
             raise ValueError("Cannot convert a vega spec to vegalite")
         if vegalite_version is None:
             raise ValueError("Must specify vegalite_version")
         return {'application/vnd.vegalite.v{}+json'.format(vegalite_version[0]): spec}
-    elif format == 'json':
+    if format == 'json':
         return {'application/json': spec}
-    else:
-        raise ValueError("format must be one of "
-                         "['png', 'svg', 'vega', 'vega-lite', 'html', 'json']")
+    raise ValueError("format must be one of "
+                     "['html', 'json', 'png', 'svg', 'pdf', 'vega', 'vega-lite']")