Improve the way to import optional modules

pygmt/datasets/tile_map.py

@@ -5,8 +5,10 @@
 
 try:
     import contextily
+
+    _HAS_CONTEXTILY = True
 except ImportError:
-    contextily = None
+    _HAS_CONTEXTILY = False
 
 import numpy as np
 import xarray as xr
@@ -107,7 +109,7 @@ def load_tile_map(region, zoom="auto", source=None, lonlat=True, wait=0, max_ret
       * y            (y) float64 -7.081e-10 -7.858e+04 ... -1.996e+07 ...
       * x            (x) float64 -2.004e+07 -1.996e+07 ... 1.996e+07 2.004e+07
     """
-    if contextily is None:
+    if not _HAS_CONTEXTILY:
         raise ImportError(
             "Package `contextily` is required to be installed to use this function. "
             "Please use `python -m pip install contextily` or "

pygmt/figure.py

@@ -8,8 +8,11 @@
 
 try:
     import IPython
+
+    _HAS_IPYTHON = True
 except ImportError:
-    IPython = None
+    _HAS_IPYTHON = False
+
 
 from pygmt.clib import Session
 from pygmt.exceptions import GMTError, GMTInvalidInput
@@ -32,7 +35,7 @@
 }
 
 # Show figures in Jupyter notebooks if available
-if IPython:
+if _HAS_IPYTHON:
     get_ipython = IPython.get_ipython()
     if get_ipython and "IPKernelApp" in get_ipython.config:  # Jupyter Notebook enabled
         SHOW_CONFIG["method"] = "notebook"
@@ -448,7 +451,7 @@ def show(self, dpi=300, width=500, method=None, waiting=0.5, **kwargs):
             )
 
         if method == "notebook":
-            if IPython is None:
+            if not _HAS_IPYTHON:
                 raise GMTError(
                     "Notebook display is selected, but IPython is not available. "
                     "Make sure you have IPython installed, "

pygmt/src/tilemap.py

@@ -6,9 +6,11 @@
 from pygmt.helpers import build_arg_string, fmt_docstring, kwargs_to_strings, use_alias
 
 try:
-    import rioxarray
+    import rioxarray  # noqa: F401  # pylint: disable=unused-import
+
+    _HAS_RIOXARRAY = True
 except ImportError:
-    rioxarray = None
+    _HAS_RIOXARRAY = False
 
 
 @fmt_docstring
@@ -114,7 +116,7 @@ def tilemap(
     """
     kwargs = self._preprocess(**kwargs)
 
-    if rioxarray is None:
+    if not _HAS_RIOXARRAY:
         raise ImportError(
             "Package `rioxarray` is required to be installed to use this function. "
             "Please use `python -m pip install rioxarray` or "

pygmt/tests/test_figure.py

@@ -3,21 +3,19 @@
 
 Doesn't include the plotting commands which have their own test files.
 """
+import importlib
 import os
 from pathlib import Path
 
-try:
-    import IPython
-except ImportError:
-    IPython = None
-
 import numpy as np
 import numpy.testing as npt
 import pytest
 from pygmt import Figure, set_display
 from pygmt.exceptions import GMTError, GMTInvalidInput
 from pygmt.helpers import GMTTempFile
 
+HAS_IPYTHON = bool(importlib.util.find_spec("IPython"))
+
 
 def test_figure_region():
     """
@@ -311,7 +309,7 @@ def test_figure_savefig_worldfile():
                 fig.savefig(fname=imgfile.name, worldfile=True)
 
 
-@pytest.mark.skipif(IPython is None, reason="run when IPython is installed")
+@pytest.mark.skipif(not HAS_IPYTHON, reason="run when IPython is installed")
 def test_figure_show():
     """
     Test that show creates the correct file name and deletes the temp dir.
@@ -352,7 +350,7 @@ def test_figure_show_invalid_method():
         fig.show(method="test")
 
 
-@pytest.mark.skipif(IPython is not None, reason="run without IPython installed")
+@pytest.mark.skipif(HAS_IPYTHON, reason="run without IPython installed")
 def test_figure_show_notebook_error_without_ipython():
     """
     Test to check if an error is raised when display method is 'notebook', but