replace StopIteration in cascade_iterator with deque.popleft()

[Mike Bayer]

run some timeit() tests to see if the StopIteration call is expensive.

[Mike Bayer]

here's the performance test for reference

from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base, declared_attr

class Base(object):
    @declared_attr
    def __tablename__(cls):
        return cls.__name__.lower()

    @declared_attr
    def id(cls):
        return Column(Integer, primary_key=True)

Base = declarative_base(cls=Base)

class A(Base):
    bs = relationship("B", backref="a")

class B(Base):
    a_id = Column(Integer, ForeignKey('a.id'))
    cs = relationship("C", backref="b")

class C(Base):
    b_id = Column(Integer, ForeignKey('b.id'))

e = create_engine('sqlite://', echo=True)
Base.metadata.create_all(e)

s = Session()

import timeit

def go():
    for i in xrange(100):
        a1 = A()
        s.add(a1)
        for j in xrange(100):
            a1.bs.append(B(cs=[for q in range(10)](C())))

for i in xrange(3):
    print timeit.Timer('from __main__ import go; go()').timeit(number=1)
    s.close()

"""
no patch:

11.4894669056
11.4846360683
11.2541160583


deque patch:

10.5410430431
10.6652979851
10.5337219238


pre-check patch:

10.9065990448
10.9252810478
10.7826881409

both patches:

10.2826850414
10.504420042
10.2249820232

no iterators:

10.0818679333
10.3000841141
10.0632379055

replace string cmp

10.0916140079
10.3783679008
10.0499939919

go back to iterator for property,
maintain backwards compat and encapsulate
usage of deque:

10.3023788929
10.1948838234
10.031416893

"""

patch is in 755aca7f5f3f33339dce4f4b6b92b8b7a9c3d180

[Mike Bayer]

Removing milestone: 0.6.5 (automated comment)