# Django 2.2.9.dev20191202104323 文档

# django.core.files.storage 源代码

    import os
    from datetime import datetime
    from urllib.parse import urljoin

    from django.conf import settings
    from django.core.exceptions import SuspiciousFileOperation
    from django.core.files import File, locks
    from django.core.files.move import file_move_safe
    from django.core.signals import setting_changed
    from django.utils import timezone
    from django.utils._os import safe_join
    from django.utils.crypto import get_random_string
    from django.utils.deconstruct import deconstructible
    from django.utils.encoding import filepath_to_uri
    from django.utils.functional import LazyObject, cached_property
    from django.utils.module_loading import import_string
    from django.utils.text import get_valid_filename

    __all__ = (
        'Storage', 'FileSystemStorage', 'DefaultStorage', 'default_storage',
        'get_storage_class',
    )

    class Storage:
        """
        A base storage class, providing some default behaviors that all other
        storage systems can inherit or override, as necessary.
        """

        # The following methods represent a public interface to private methods.
        # These shouldn't be overridden by subclasses unless absolutely necessary.

        def open(self, name, mode='rb'):
            """Retrieve the specified file from storage."""
            return self._open(name, mode)

        def save(self, name, content, max_length=None):
            """
            Save new content to the file specified by name. The content should be
            a proper File object or any Python file-like object, ready to be read
            from the beginning.
            """
            # Get the proper name for the file, as it will actually be saved.
            if name is None:
                name = content.name

            if not hasattr(content, 'chunks'):
                content = File(content, name)

            name = self.get_available_name(name, max_length=max_length)
            return self._save(name, content)

        # These methods are part of the public API, with default implementations.

        def get_valid_name(self, name):
            """
            Return a filename, based on the provided filename, that's suitable for
            use in the target storage system.
            """
            return get_valid_filename(name)

        def get_available_name(self, name, max_length=None):
            """
            Return a filename that's free on the target storage system and
            available for new content to be written to.
            """
            dir_name, file_name = os.path.split(name)
            file_root, file_ext = os.path.splitext(file_name)
            # If the filename already exists, add an underscore and a random 7
            # character alphanumeric string (before the file extension, if one
            # exists) to the filename until the generated filename doesn't exist.
            # Truncate original name if required, so the new filename does not
            # exceed the max_length.
            while self.exists(name) or (max_length and len(name) > max_length):
                # file_ext includes the dot.
                name = os.path.join(dir_name, "%s_%s%s" % (file_root, get_random_string(7), file_ext))
                if max_length is None:
                    continue
                # Truncate file_root if max_length exceeded.
                truncation = len(name) - max_length
                if truncation > 0:
                    file_root = file_root[:-truncation]
                    # Entire file_root was truncated in attempt to find an available filename.
                    if not file_root:
                        raise SuspiciousFileOperation(
                            'Storage can not find an available filename for "%s". '
                            'Please make sure that the corresponding file field '
                            'allows sufficient "max_length".' % name
                        )
                    name = os.path.join(dir_name, "%s_%s%s" % (file_root, get_random_string(7), file_ext))
            return name

        def generate_filename(self, filename):
            """
            Validate the filename by calling get_valid_name() and return a filename
            to be passed to the save() method.
            """
            # `filename` may include a path as returned by FileField.upload_to.
            dirname, filename = os.path.split(filename)
            return os.path.normpath(os.path.join(dirname, self.get_valid_name(filename)))

        def path(self, name):
            """
            Return a local filesystem path where the file can be retrieved using
            Python's built-in open() function. Storage systems that can't be
            accessed using open() should *not* implement this method.
            """
            raise NotImplementedError("This backend doesn't support absolute paths.")

        # The following methods form the public API for storage systems, but with
        # no default implementations. Subclasses must implement *all* of these.

        def delete(self, name):
            """
            Delete the specified file from the storage system.
            """
            raise NotImplementedError('subclasses of Storage must provide a delete() method')

        def exists(self, name):
            """
            Return True if a file referenced by the given name already exists in the
            storage system, or False if the name is available for a new file.
            """
            raise NotImplementedError('subclasses of Storage must provide an exists() method')

        def listdir(self, path):
            """
            List the contents of the specified path. Return a 2-tuple of lists:
            the first item being directories, the second item being files.
            """
            raise NotImplementedError('subclasses of Storage must provide a listdir() method')

        def size(self, name):
            """
            Return the total size, in bytes, of the file specified by name.
            """
            raise NotImplementedError('subclasses of Storage must provide a size() method')

        def url(self, name):
            """
            Return an absolute URL where the file's contents can be accessed
            directly by a Web browser.
            """
            raise NotImplementedError('subclasses of Storage must provide a url() method')

        def get_accessed_time(self, name):
            """
            Return the last accessed time (as a datetime) of the file specified by
            name. The datetime will be timezone-aware if USE_TZ=True.
            """
            raise NotImplementedError('subclasses of Storage must provide a get_accessed_time() method')

        def get_created_time(self, name):
            """
            Return the creation time (as a datetime) of the file specified by name.
            The datetime will be timezone-aware if USE_TZ=True.
            """
            raise NotImplementedError('subclasses of Storage must provide a get_created_time() method')

        def get_modified_time(self, name):
            """
            Return the last modified time (as a datetime) of the file specified by
            name. The datetime will be timezone-aware if USE_TZ=True.
            """
            raise NotImplementedError('subclasses of Storage must provide a get_modified_time() method')

    @deconstructible
    class FileSystemStorage(Storage):
        """
        Standard filesystem storage
        """
        # The combination of O_CREAT and O_EXCL makes os.open() raise OSError if
        # the file already exists before it's opened.
        OS_OPEN_FLAGS = os.O_WRONLY | os.O_CREAT | os.O_EXCL | getattr(os, 'O_BINARY', 0)

        def __init__(self, location=None, base_url=None, file_permissions_mode=None,
                     directory_permissions_mode=None):
            self._location = location
            self._base_url = base_url
            self._file_permissions_mode = file_permissions_mode
            self._directory_permissions_mode = directory_permissions_mode
            setting_changed.connect(self._clear_cached_properties)

        def _clear_cached_properties(self, setting, **kwargs):
            """Reset setting based property values."""
            if setting == 'MEDIA_ROOT':
                self.__dict__.pop('base_location', None)
                self.__dict__.pop('location', None)
            elif setting == 'MEDIA_URL':
                self.__dict__.pop('base_url', None)
            elif setting == 'FILE_UPLOAD_PERMISSIONS':
                self.__dict__.pop('file_permissions_mode', None)
            elif setting == 'FILE_UPLOAD_DIRECTORY_PERMISSIONS':
                self.__dict__.pop('directory_permissions_mode', None)

        def _value_or_setting(self, value, setting):
            return setting if value is None else value

        @cached_property
        def base_location(self):
            return self._value_or_setting(self._location, settings.MEDIA_ROOT)

        @cached_property
        def location(self):
            return os.path.abspath(self.base_location)

        @cached_property
        def base_url(self):
            if self._base_url is not None and not self._base_url.endswith('/'):
                self._base_url += '/'
            return self._value_or_setting(self._base_url, settings.MEDIA_URL)

        @cached_property
        def file_permissions_mode(self):
            return self._value_or_setting(self._file_permissions_mode, settings.FILE_UPLOAD_PERMISSIONS)

        @cached_property
        def directory_permissions_mode(self):
            return self._value_or_setting(self._directory_permissions_mode, settings.FILE_UPLOAD_DIRECTORY_PERMISSIONS)

        def _open(self, name, mode='rb'):
            return File(open(self.path(name), mode))

        def _save(self, name, content):
            full_path = self.path(name)

            # Create any intermediate directories that do not exist.
            directory = os.path.dirname(full_path)
            if not os.path.exists(directory):
                try:
                    if self.directory_permissions_mode is not None:
                        # os.makedirs applies the global umask, so we reset it,
                        # for consistency with file_permissions_mode behavior.
                        old_umask = os.umask(0)
                        try:
                            os.makedirs(directory, self.directory_permissions_mode)
                        finally:
                            os.umask(old_umask)
                    else:
                        os.makedirs(directory)
                except FileExistsError:
                    # There's a race between os.path.exists() and os.makedirs().
                    # If os.makedirs() fails with FileExistsError, the directory
                    # was created concurrently.
                    pass
            if not os.path.isdir(directory):
                raise IOError("%s exists and is not a directory." % directory)

            # There's a potential race condition between get_available_name and
            # saving the file; it's possible that two threads might return the
            # same name, at which point all sorts of fun happens. So we need to
            # try to create the file, but if it already exists we have to go back
            # to get_available_name() and try again.

            while True:
                try:
                    # This file has a file path that we can move.
                    if hasattr(content, 'temporary_file_path'):
                        file_move_safe(content.temporary_file_path(), full_path)

                    # This is a normal uploadedfile that we can stream.
                    else:
                        # The current umask value is masked out by os.open!
                        fd = os.open(full_path, self.OS_OPEN_FLAGS, 0o666)
                        _file = None
                        try:
                            locks.lock(fd, locks.LOCK_EX)
                            for chunk in content.chunks():
                                if _file is None:
                                    mode = 'wb' if isinstance(chunk, bytes) else 'wt'
                                    _file = os.fdopen(fd, mode)
                                _file.write(chunk)
                        finally:
                            locks.unlock(fd)
                            if _file is not None:
                                _file.close()
                            else:
                                os.close(fd)
                except FileExistsError:
                    # A new name is needed if the file exists.
                    name = self.get_available_name(name)
                    full_path = self.path(name)
                else:
                    # OK, the file save worked. Break out of the loop.
                    break

            if self.file_permissions_mode is not None:
                os.chmod(full_path, self.file_permissions_mode)

            # Store filenames with forward slashes, even on Windows.
            return name.replace('\\', '/')

        def delete(self, name):
            assert name, "The name argument is not allowed to be empty."
            name = self.path(name)
            # If the file or directory exists, delete it from the filesystem.
            try:
                if os.path.isdir(name):
                    os.rmdir(name)
                else:
                    os.remove(name)
            except FileNotFoundError:
                # FileNotFoundError is raised if the file or directory was removed
                # concurrently.
                pass

        def exists(self, name):
            return os.path.exists(self.path(name))

        def listdir(self, path):
            path = self.path(path)
            directories, files = [], []
            for entry in os.scandir(path):
                if entry.is_dir():
                    directories.append(entry.name)
                else:
                    files.append(entry.name)
            return directories, files

        def path(self, name):
            return safe_join(self.location, name)

        def size(self, name):
            return os.path.getsize(self.path(name))

        def url(self, name):
            if self.base_url is None:
                raise ValueError("This file is not accessible via a URL.")
            url = filepath_to_uri(name)
            if url is not None:
                url = url.lstrip('/')
            return urljoin(self.base_url, url)

        def _datetime_from_timestamp(self, ts):
            """
            If timezone support is enabled, make an aware datetime object in UTC;
            otherwise make a naive one in the local timezone.
            """
            if settings.USE_TZ:
                # Safe to use .replace() because UTC doesn't have DST
                return datetime.utcfromtimestamp(ts).replace(tzinfo=timezone.utc)
            else:
                return datetime.fromtimestamp(ts)

        def get_accessed_time(self, name):
            return self._datetime_from_timestamp(os.path.getatime(self.path(name)))

        def get_created_time(self, name):
            return self._datetime_from_timestamp(os.path.getctime(self.path(name)))

        def get_modified_time(self, name):
            return self._datetime_from_timestamp(os.path.getmtime(self.path(name)))

    def get_storage_class(import_path=None):
        return import_string(import_path or settings.DEFAULT_FILE_STORAGE)

    class DefaultStorage(LazyObject):
        def _setup(self):
            self._wrapped = get_storage_class()()

    default_storage = DefaultStorage()