django1/django/utils/image.py

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# -*- coding: utf-8 -*-
"""
To provide a shim layer over Pillow/PIL situation until the PIL support is
removed. See #19934.
Combinations To Account For
===========================
* Pillow:
* never has ``_imaging`` under any Python
* has the ``Image.alpha_composite``, which may aid in detection
* PIL
* CPython 2.x may have _imaging (& work)
* CPython 2.x may *NOT* have _imaging (broken & needs a error message)
* CPython 3.x doesn't work
* PyPy will *NOT* have _imaging (but works?)
* On some platforms (Homebrew and RHEL6 reported) _imaging isn't available,
the needed import is from PIL import _imaging (refs #21355)
Restated, that looks like:
* If we're on Python 2.x, it could be either Pillow or PIL:
* If ``import _imaging`` results in ``ImportError``, either they have a
working Pillow installation or a broken PIL installation, so we need to
detect further:
* To detect, we first ``import Image``.
* If ``Image`` has a ``alpha_composite`` attribute present, only Pillow
has this, so we assume it's working.
* If ``Image`` DOES NOT have a ``alpha_composite``attribute, it must be
PIL & is a broken (likely C compiler-less) install, which we need to
warn the user about.
* If ``import _imaging`` works, it must be PIL & is a working install.
* Python 3.x
* If ``import Image`` works, it must be Pillow, since PIL isn't Python 3.x
compatible.
* PyPy
* If ``import _imaging`` results in ``ImportError``, it could be either
Pillow or PIL, both of which work without it on PyPy, so we're fine.
Approach
========
* Attempt to import ``Image``
* ``ImportError`` - nothing is installed, toss an exception
* Either Pillow or the PIL is installed, so continue detecting
* Attempt to ``hasattr(Image, 'alpha_composite')``
* If it works, it's Pillow & working
* If it fails, we've got a PIL install, continue detecting
* The only option here is that we're on Python 2.x or PyPy, of which
we only care about if we're on CPython.
* If we're on CPython, attempt to ``from PIL import _imaging`` and
``import _imaging``
* ``ImportError`` - Bad install, toss an exception
"""
from __future__ import unicode_literals
import warnings
from django.core.exceptions import ImproperlyConfigured
from django.utils.translation import ugettext_lazy as _
Image = None
_imaging = None
ImageFile = None
def _detect_image_library():
global Image
global _imaging
global ImageFile
# Skip re-attempting to import if we've already run detection.
if Image is not None:
return Image, _imaging, ImageFile
# Assume it's not there.
PIL_imaging = False
try:
# Try from the Pillow (or one variant of PIL) install location first.
from PIL import Image as PILImage
except ImportError as err:
try:
# If that failed, try the alternate import syntax for PIL.
import Image as PILImage
except ImportError as err:
# Neither worked, so it's likely not installed.
raise ImproperlyConfigured(
_("Neither Pillow nor PIL could be imported: %s") % err
)
# ``Image.alpha_composite`` was added to Pillow in SHA: e414c6 & is not
# available in any version of the PIL.
if hasattr(PILImage, 'alpha_composite'):
PIL_imaging = False
else:
# We're dealing with the PIL. Determine if we're on CPython & if
# ``_imaging`` is available.
import platform
# This is the Alex Approved™ way.
# See http://mail.python.org/pipermail//pypy-dev/2011-November/008739.html
if platform.python_implementation().lower() == 'cpython':
# We're on CPython (likely 2.x). Since a C compiler is needed to
# produce a fully-working PIL & will create a ``_imaging`` module,
# we'll attempt to import it to verify their kit works.
try:
from PIL import _imaging as PIL_imaging
except ImportError:
try:
import _imaging as PIL_imaging
except ImportError as err:
raise ImproperlyConfigured(
_("The '_imaging' module for the PIL could not be "
"imported: %s") % err
)
# Try to import ImageFile as well.
try:
from PIL import ImageFile as PILImageFile
except ImportError:
# This import cannot fail unless Pillow/PIL install is completely
# broken (e.g. missing Python modules).
import ImageFile as PILImageFile
# Finally, warn about deprecation...
if PIL_imaging is not False:
warnings.warn(
"Support for the PIL will be removed in Django 1.8. Please " +
"uninstall it & install Pillow instead.",
DeprecationWarning
)
return PILImage, PIL_imaging, PILImageFile
Image, _imaging, ImageFile = _detect_image_library()