article on Python 2.5 features

Re: article on Python 2.5 features

Beliavsky wrote:The article is nice overall, but I did not like the part about enhanced
generators. For instance, the sentence "The new interactive send()
empowers
generators to implement co-routines", could be debated. Also, it gives
you the false impression that you could not interact with Python 2.2
generators ("interact" in the sense of the article). IMO the important
bit about Python 2.5 generators is that you can send exceptions to
a generator, all the other features can be emulated even using revious
versions of Python.
For instance, here is an emulation of his tokenizer using Python 2.2
generators and a helper 'read_eval_yiel d_loop' class:

# morally turns a Python 2.2+ generator into a Python 2.5 generator
class read_eval_yield _loop(object):
def __init__(self, gen, *args, **kw):
self._arg = None
self._it = gen(iter(lambda : self._arg, StopIteration), *args,
**kw)
def __iter__(self):
return self._it
def send(self, arg):
self._arg = arg
return self._it.next()
def next(self):
return self.send(None)

# copied from the article with very minor changes
def tokenizer3(read , text, sep):
try:
while True:
token = ''
while text[0] == sep:
text = text[1:]

index = 0
while text[index] != sep:
token += text[index]
index += 1
yield token
new_sep = read.next()
if new_sep != None:
sep = new_sep
text = text[index:]
except IndexError:
if token != '':
yield token

if __name__=='__ma in__':
print '--- Smart Python 2.2+ tokenizer ---'
g = read_eval_yield _loop(tokenizer 3, text, ' ')
for t in g:
print t
if t == 'comma':
g.send(',')

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