get renderer fcn (#113)

* test get renderer fcn

* fix restore_backend

* add os name

* move restore_backend to init

* add test_set_size

* more info on size

* device_pixel_ratio

* dpi=1000

* use finally

* move and fix fcns

Author: mathause

mplotutils/__init__.py

@@ -8,6 +8,7 @@
 from .cartopy_utils import *
 from .colormaps import *
 from .map_layout import set_map_layout
+from .mpl import _get_renderer
 from .xrcompat import *
 
 autodraw(True)

mplotutils/mpl.py

@@ -0,0 +1,15 @@
+import matplotlib
+
+
+def _get_renderer(fig):
+
+    if hasattr(fig.canvas, "get_renderer"):
+        return fig.canvas.get_renderer()
+    elif hasattr(fig, "_get_renderer"):
+        return fig._get_renderer()
+
+    backend = matplotlib.get_backend()
+
+    raise AttributeError(
+        f"Could not find a renderer for the '{backend}' backend. Please raise an issue"
+    )

mplotutils/tests/__init__.py

@@ -1,6 +1,8 @@
 import contextlib
 
+import matplotlib
 import matplotlib.pyplot as plt
+import pytest
 
 
 @contextlib.contextmanager
@@ -21,3 +23,30 @@ def subplots_context(*args, **kwargs):
         yield fig, axs
     finally:
         plt.close(fig)
+
+
+@contextlib.contextmanager
+def restore_backend(backend):
+
+    current_backend = plt.get_backend()
+
+    try:
+        _set_backend(backend)
+        yield
+    finally:
+        plt.switch_backend(current_backend)
+
+
+def _set_backend(backend):
+
+    # WebAgg requires tornado, but this is only checked at runtime
+    if backend == "WebAgg":
+        try:
+            import tornado  # noqa: F401
+        except ImportError:
+            pytest.skip(backend)
+
+    try:
+        matplotlib.use(backend)
+    except ImportError:
+        pytest.skip(backend)

mplotutils/tests/test_get_renderer.py

@@ -0,0 +1,15 @@
+import matplotlib
+import pytest
+
+from mplotutils import _get_renderer
+
+from . import figure_context, restore_backend
+
+
+@pytest.mark.parametrize("backend", matplotlib.rcsetup.all_backends)
+def test_get_renderer(backend):
+
+    with restore_backend(backend):
+
+        with figure_context() as f:
+            _get_renderer(f)