Trying to put a generator inside a with statement. It seems it is not possible.

with_gen.py

from exceptions import StopIteration, GeneratorExit


class WithThis(object):
    """
    Open is a built in - can't override __exit__ or subclass it so wrap it :-(
    """

    def __init__(self,this=None):
        print "  __init__"
        if this is None:
            this = {}
        self.this = this
        
    def __enter__(self):
          print "  __enter__"
          return self.this
          
    def __exit__(self, exctype, value, tb):
        print "  __exit__: %s,%s" % (exctype, value)
        self.this.clear()
        if exctype == StopIteration:
            print 'Haha!'
            return True
        elif exctype == GeneratorExit:
            print "Hoho!"
            raise GeneratorExit
            return False
        else:
            return True
        
        
def gen_with(this=None):
    if this is None:
            this = {}      
    things = ['eat','poop','you','cat']
    for i, item in enumerate(things):
        with WithThis(this=this) as ths:
            ths[item] = i
            yield ths
 
def gen_print(d=None):
    print "GenPrint: '%s'" % d

def gen_error(d=None):
    print "GenError: '%s'" % d
    del d['not a key']


def coroutine(func):
    """From Beazley"""
    def start(*arg, **kwargs):
        g = func(*arg, **kwargs)
        g.next()
        return g
    return start
        


@coroutine
def co_with(target, this=None):
    if this is None:
        this = {}
    print "co_with ready to recieve file names"
    i = 0
    while True:
        with WithThis(this=this) as ths:
            thing = (yield)
            ths[thing] = i
            target.send(ths)
            i += 1
        
@coroutine
def co_print():
    print "co_print ready to recieve file names"
    while True:
        d = (yield)
        print "CoPrint: %s" % d
        
     
@coroutine
def co_error():
    print "co_error ready to recieve file names"
    while True:
        d = (yield)
        print "CoError: %s" % d
        del d['not a key']
    
        
        


d = {}
print "Try with a generator inside the with"
print "First case, no exceptions raised:"
g = gen_with(this=d)
for item in g:
    gen_print(d)

g = gen_with(this=d)
print "Second case, Key Error causes the generator to Fail. With is not allowed to catch Generator Exit"
for item in g:
    gen_error(d)

print "%%%%%%% Now try with coroutines %%%%%%%%%%"

d= {}
e = {}
co_without_error = co_with(co_print(), this=d)
co_with_error = co_with(co_error(), this = e)

things = ['eat','poop','you','cat']

print "First case, no exceptions"
for item in things:
    co_without_error.send(item)

print "Second case, Cause a Key Error"
for item in things:
    co_with_error.send(item)