From ff64a0e935cbd6fe0b1540a7881d8946bdb00ea7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nico=20Schl=C3=B6mer?= <nico.schloemer@gmail.com>
Date: Mon, 20 Dec 2021 06:38:28 +0100
Subject: [PATCH] make meshio an optional dependency (#1939)

* make meshio an optional dependency

* add import guards

* make flake8 happy

Co-authored-by: Alex Kaszynski <akascap@gmail.com>
---
 pyvista/core/filters/unstructured_grid.py |  3 +--
 pyvista/utilities/errors.py               | 10 ++++++----
 pyvista/utilities/fileio.py               | 21 ++++++++++++++++++---
 requirements_test.txt                     |  1 +
 setup.py                                  |  5 +++--
 5 files changed, 29 insertions(+), 11 deletions(-)

diff --git a/pyvista/core/filters/unstructured_grid.py b/pyvista/core/filters/unstructured_grid.py
index 00d1d0b5dc..f5a6a4fab0 100644
--- a/pyvista/core/filters/unstructured_grid.py
+++ b/pyvista/core/filters/unstructured_grid.py
@@ -1,10 +1,9 @@
 """Filters module with a class to manage filters/algorithms for unstructured grid datasets."""
 from functools import wraps
 
-import pyvista
 from pyvista import abstract_class
-from pyvista.core.filters.poly_data import PolyDataFilters
 from pyvista.core.filters.data_set import DataSetFilters
+from pyvista.core.filters.poly_data import PolyDataFilters
 
 
 @abstract_class
diff --git a/pyvista/utilities/errors.py b/pyvista/utilities/errors.py
index 11384b0618..4e0563f3fa 100644
--- a/pyvista/utilities/errors.py
+++ b/pyvista/utilities/errors.py
@@ -281,12 +281,14 @@ def __init__(self, additional=None, ncol=3, text_width=80, sort=False,
 
         """
         # Mandatory packages.
-        core = ['pyvista', 'vtk', 'numpy', 'imageio', 'appdirs', 'scooby',
-                'meshio']
+        core = ['pyvista', 'vtk', 'numpy', 'imageio', 'appdirs', 'scooby']
 
         # Optional packages.
-        optional = ['matplotlib', 'pyvistaqt', 'PyQt5', 'IPython', 'colorcet',
-                    'cmocean', 'ipyvtklink', 'scipy', 'itkwidgets', 'tqdm']
+        optional = [
+            'matplotlib', 'pyvistaqt', 'PyQt5', 'IPython', 'colorcet',
+            'cmocean', 'ipyvtklink', 'scipy', 'itkwidgets', 'tqdm',
+            'meshio',
+        ]
 
         # Information about the GPU - bare except in case there is a rendering
         # bug that the user is trying to report.
diff --git a/pyvista/utilities/fileio.py b/pyvista/utilities/fileio.py
index 64382b5032..5441c8c64f 100644
--- a/pyvista/utilities/fileio.py
+++ b/pyvista/utilities/fileio.py
@@ -282,7 +282,9 @@ def read(filename, attrs=None, force_ext=None, file_format=None):
        * ``'.foam'``
 
     .. note::
-       See https://github.com/nschloe/meshio for formats supported by ``meshio``.
+       See https://github.com/nschloe/meshio for formats supported by
+       ``meshio``. Be sure to install ``meshio`` with ``pip install
+       meshio`` if you wish to use it.
 
     Parameters
     ----------
@@ -635,7 +637,13 @@ def from_meshio(mesh):
 
 def read_meshio(filename, file_format=None):
     """Read any mesh file using meshio."""
-    import meshio
+    try:
+        import meshio
+    except ImportError:  # pragma: no cover
+        raise ImportError(
+            "To use this feature install meshio with:\n\n"
+            "pip install meshio"
+        )
 
     # Make sure relative paths will work
     filename = os.path.abspath(os.path.expanduser(str(filename)))
@@ -673,7 +681,14 @@ def save_meshio(filename, mesh, file_format=None, **kwargs):
     >>> pyvista.save_meshio('mymesh.inp', sphere)  # doctest:+SKIP
 
     """
-    import meshio
+    try:
+        import meshio
+    except ImportError:  # pragma: no cover
+        raise ImportError(
+            "To use this feature install meshio with:\n\n"
+            "pip install meshio"
+        )
+
     from meshio.vtk._vtk import vtk_to_meshio_type
 
     # Make sure relative paths will work
diff --git a/requirements_test.txt b/requirements_test.txt
index 06e05f0c31..347e5ad95d 100644
--- a/requirements_test.txt
+++ b/requirements_test.txt
@@ -19,3 +19,4 @@ param==1.10.1
 ipygany
 pytest-xdist
 pythreejs
+meshio>=4.0.3, <5.0
diff --git a/setup.py b/setup.py
index 6bad131c3f..da3d7e6558 100644
--- a/setup.py
+++ b/setup.py
@@ -19,7 +19,6 @@
                     'pillow',
                     'appdirs',
                     'scooby>=0.5.1',
-                    'meshio>=4.0.3, <5.0',
                     'vtk',
                     'dataclasses;python_version=="3.6"',
                     'typing_extensions;python_version<="3.7"',
@@ -70,6 +69,8 @@
     python_requires='>=3.6.*',
     install_requires=install_requires,
     extras_require={
-        'colormaps': ['matplotlib', 'colorcet', 'cmocean']
+        'all': ['matplotlib', 'colorcet', 'cmocean', 'meshio'],
+        'colormaps': ['matplotlib', 'colorcet', 'cmocean'],
+        'io': ['meshio>=4.0.3, <5.0'],
     },
 )