Chris Angelico <ros...@gmail.com>:
> On Tue, Mar 29, 2016 at 12:40 AM, Marko Rauhamaa <ma...@pacujo.net> wrote:
>> Dan Sommers <d...@tombstonezero.net>:
>>
>>> On Mon, 28 Mar 2016 11:58:54 +0300, Marko Rauhamaa wrote:
>>>
>>>> As for Python, I don't feel a great need for anonymous functions.
>>>> However, I keep running into a need for anonymous classes, or,
>>>> rather, classless objects. Not a biggie. I just create a one-off
>>>> inner class and instantiate it, but I do appreciate Java's syntactic
>>>> innovation.
>>>
>>> And I always curse Java for having to create an inner class and a
>>> method when all I need is a simple function. :-)
>>>
>>> I think it's Steven D'Aprano who keeps pointing out that you can
>>> always name your tiny helper functions instead of using lambda:
>>>
>>> def some_complex_function():
>>> def f(x) = x + 2
>>> some_library_that_wants_a_callback(f)
>>> some_library_that_wants_a_callback(lambda x: x + 2)
>>>
>>> Both calls to some_library_that_wants_a_callback run the same.
>>
>> Yes, but I've come to realize that I quite often need more than a
>> function: I need an object with behavior. The solution is to use a
>> "helper" class.
>
> Can you give an example of code that would benefit from a
> "lambda-class" construct?
Here's a recent example:
========================================================================
def process(self, source):
awk = self
class Source(snake.FieldSource):
def emit_fields(self):
for fields in snake.get_fields(
source, awk.encoding, awk.errors,
awk.eol, awk.delim):
if awk.selector is None or awk.selector(fields):
yield [ fields[i] for i in awk.columns ]
return Source(self.encoding, self.errors, self.eol, self.delim)
========================================================================
Here's another, older one:
========================================================================
def __init__(self, server, sock, domain, peer):
super().__init__(server, sock)
conn = self
client_ip = peer[0]
[...]
class SPF_HELO(STATE):
def terminate(self):
conn.resume()
conn.spf_query.cancel()
conn.close()
if conn.timer is not None:
conn.timer.cancel()
conn.timer = None
conn.set_state(ZOMBIE)
def handle_spf_verdict(self, verdict, reason, *capabilities):
conn.resume()
conn.log("verdict {} reason {}".format(verdict, reason))
# RFC 4408 ยง2.5.5 calls for leniency for SoftFail
#if verdict in [ SPFClient.FAIL, SPFClient.SOFT_FAIL ]:
if verdict in [ SPFClient.FAIL ]:
conn.respond(550, "SPF check failed: {}".format(reason))
conn.set_state(IDLE)
return
conn.respond(250, server.domain, *capabilities)
conn.set_state(IDLE)
========================================================================
Marko
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