如何在无限循环中异常终止Python协程？

Question

My following code simulate UNIX pipes :

@coroutine
def grep(cible,motif):
    while True:
        line = yield
        if motif in line:
            cible.send("{}".format(line))

@coroutine
def subst(cible,old,new):
    while True:
        line = yield
        line=line.replace(old,new)
        cible.send("{}".format(line))

@coroutine
def lc(cible):
    nl = 0  
    while True:
            line = yield
            cible.send("{}".format(line))
    print(nl) # obvously not like that ! But how ??

@coroutine
def echo():
    while True:
        line = yield
        print(line)

For example :

pipe = grep(subst(lc(echo()),"old","new")," ")
for line in ["wathever","it's an old string","old_or_new","whitespaces for grep"]:
    pipe.send(line)

gives :

it's an new string
whitespaces for grep

lc must count the lines (like wc) and must return it at the end. How can I do this ?

Answer 1

I didn't know than a coroutine can be closed. So the solution of my problem is :

@coroutine
def lc(cible):
  nl = 0  
  while True:
      try:
        nl += 1  
        line = yield
      except GeneratorExit:
        cible.send("{}".format(nl))
        raise

and this needs in main :

pipe.close()

Thanks you very much RobertB !