gistfile1.py

class BinData(ObjectRef):
        """
                Stores (a reference to) one data file

                This object implements a content-based file system: the hash of the
                file contents is an index.
                """
        storage_seq = Column(Integer, autoincrement=True, unique=True)
        mime_id = Column(Integer, ForeignKey(MIMEtype.id), nullable=False, index=True)
        mime = relationship(MIMEtype, primaryjoin=mime_id==MIMEtype.id)

        name = Column(Unicode(100), nullable=False)
        hash = Column(Unicode(33), nullable=True, unique=True) ## NULL if deleted, 404's without hitting the file system
        timestamp = Column(DateTime,default=datetime.utcnow)
        size = Column(Integer)
        […]
        def _get_chars(self):
                """This creates a unique path+filename for storage."""
                if self.storage_seq is None:
                        db.flush()
                        db.refresh(self,('storage_seq',))
                        if self.storage_seq is None: ## sqlite, probably
                                from sqlalchemy import func
                                self.storage_seq = (db.query(func.max(BinData.storage_seq)).scalar() or 0) +1
                                db.flush()
                assert self.storage_seq, repr(self)
                id = self.storage_seq-1
                chars = "abcdefghjk" ## 100 files per end directory (long names)
                midchars = "abcdefghjkmnopqr" ## 256 subdirectories (short names)
                fc = []
                flast = chars[id % len(chars)]
                id = id // len(chars)
                flast += chars[id % len(chars)]
                id = id // len(chars)
                while id:
                        id -= 1
                        c = midchars[id % len(midchars)]
                        id = id // len(midchars)
                        c = midchars[id % len(midchars)] + c
                        id = id // len(midchars)
                        fc.insert(0,c)
                fc.append("_")
                fc.append(self.name+"_"+self.hash[0:10]+flast)
                if self.mime.ext:
                        fc[-1] += "."+self.mime.ext
                return fc

try:
        from hashlib import sha1
except ImportError:
        from sha import sha as sha1
def hash_data(content):
        """
        Create an URL-compatible ASCII hash
        """
        from base64 import b64encode
        return b64encode(sha1(content).digest(),altchars=str("-_")).rstrip("=")

## The mysql driver ignores autoincrement on non-primary-key columns.
## Workaround:
from sqlalchemy import event
from sqlalchemy.schema import DDL
event.listen(BinData.__table__, 'after_create',
            DDL("ALTER TABLE bindata CHANGE storage_seq storage_seq INT AUTO_INCREMENT NOT NULL", on="mysql"))