setup.py: Test for and fix pillow DLL error in Windows

setup.py

@@ -409,6 +409,11 @@ def packages_need_install(self) -> bool:
  """bool: ``True`` if there are packages available that need to be installed """
  return bool(self._missing_packages or self._conda_missing_packages)
 
+ @property
+ def required_packages(self) -> list[Requirement]:
+ """ list: The full list of required packages """
+ return self._required_packages
+
  @property
  def to_install(self) -> list[Requirement]:
  """ list: The required packages that need to be installed """
@@ -1031,6 +1036,7 @@ def __init__(self, environment: Environment, is_gui: bool = False) -> None:
  logger.info("Installing Required Python Packages. This may take some time...")
  self._install_setup_packages()
  self._install_missing_dep()
+ self._post_install_checks()
  if self._env.updater:
  return
  if not _INSTALL_FAILED:
@@ -1161,7 +1167,7 @@ def _from_conda(self,
  if channels is not None:
  if len(channels) > 1 and "defaults" in channels:
  logger.debug("Setting default channel to lowest priority")
- channels = [c for c in channels if c != "defaults"] + ["defaults"]
+ channels = tuple([c for c in channels if c != "defaults"] + ["defaults"])
  for channel in channels:
  condaexe.extend(["-c", channel])
  condaexe.append("--override-channels")
@@ -1211,6 +1217,42 @@ def _from_pip(self, package: list[str] | str, extra_args: str = "") -> None:
  global _INSTALL_FAILED # pylint:disable=global-statement
  _INSTALL_FAILED = True
 
+ def _downgrade_pillow(self) -> None:
+ """ Downgrade pillow from the Conda version to the pip version. This is generally seen as
+ a bad idea, but is currently the best solution available. """
+ pillow = next((p for p in self._packages.required_packages if p.name == "pillow"), "")
+ if not pillow:
+ logger.debug("Pillow is not a required package")
+ return
+ logger.debug("Re-installing pillow from pip")
+ self._from_pip(str(pillow), extra_args="--upgrade --force-reinstall")
+
+ def _post_install_checks(self) -> None:
+ """ Any post installation actions to perform.
+
+ Currently there is an issue on some Conda Windows installs where the following error
+ occurs when importing Pillow:
+
+ ImportError: DLL load failed while importing _imaging: The specified module could not be
+ found.
+
+ At the time of writing there is no clear indication of why this occurs, but the
+ installation of Pillow from pip appears to remedy the situation
+ """
+ if self._env.os_version[0] != "Windows" or not self._env.is_conda:
+ return
+
+ try:
+ from PIL import Image # noqa:F401 pylint:disable=unused-import,import-outside-toplevel
+ except ImportError as err:
+ if "DLL load failed while importing _imaging" in str(err):
+ logger.debug("Handling pillow import error: '%s'", str(err))
+ self._downgrade_pillow()
+ return
+ logger.warning("Unhandled error when checking Pillow: %s", str(err))
+ return
+ logger.debug("Pillow check passed")
+
 
 class ProgressBar():
  """ Simple progress bar using STDLib for intercepting Conda installs and keeping the
@@ -1407,7 +1449,7 @@ def _print_pip(self, text: bytes) -> None:
  """
  pkg = self._re_pip_pkg.match(text)
  if pkg:
- logger.debug("Collected pip package '%s'", pkg)
+ logger.debug("Collected pip package %s", pkg)
  self._pip_pkg = pkg.groupdict()["lib"].decode("utf-8", errors="replace")
  return
  data = self._re_pip.search(text)