while loop with the condition used in the body

[Ulrich Eckhardt]

Hi!

I'm looking for a way to write code similar to this C code:

while(rq = get_request(..)) {
handle_request(rq);
}

Currently I'm doing

while True:
rq = get_request(...)
if not rq:
break
handle_request(rq)

in Python 2.6. Any suggestions how to rewrite that?

Uli

 

[Arnaud Delobelle]

Hi!

I'm looking for a way to write code similar to this C code:

while(rq = get_request(..)) {
handle_request(rq);
}

Currently I'm doing

while True:
rq = get_request(...)
if not rq:
break
handle_request(rq)

in Python 2.6. Any suggestions how to rewrite that?

This is the common idiom.

 

[Peter Otten]

I'm looking for a way to write code similar to this C code:

while(rq = get_request(..)) {
handle_request(rq);
}

Currently I'm doing

while True:
rq = get_request(...)
if not rq:
break
handle_request(rq)

in Python 2.6. Any suggestions how to rewrite that?

Assuming get_request(...) is called with the same arguments on each
iteration and uses None to signal that there is no more data:

from functools import partial

for rq in iter(partial(get_request, ...), None):
handle_request(rq)

Peter

 

[Peter Otten]

and the next step on from this is to realise that the problem isn't how to
code the calls to get_request(), the problem is actually that
get_request() itself isn'ty Pythonic. Rewrite it as a generator, rename it
to reflect that it now generates a sequence of requests and the code
becomes:

for rq in incoming_requests(...):
handle_request(rq)

....and a likely implementation would be

def incoming_requests(...):
while True:
rq = ... # inlined version of get_request()
if not rq:
break
yield rq

In other words: It's turtles all the way down...

Peter

 

[Ulrich Eckhardt]

...and a likely implementation would be

def incoming_requests(...):
while True:
rq = ... # inlined version of get_request()
if not rq:
break
yield rq

In other words: It's turtles all the way down...

Almost. While it moves the ugliness, at least it allows separating the
iteration logic from the handling logic, which is already a big step ahead!

That said, there is:

with <expression> as <name>:
...

so why not:

while <expression> as <name>:
...

and also:

if <expression> as <name>:
...


Thanks to everybody for their input!

Uli

 

[Gregory Ewing]

so why not:

while <expression> as <name>:
...

and also:

if <expression> as <name>:
...

This sort of thing has been suggested repeatedly in the
past, and it's always been rejected. That's not likely to
change. Look up the past threads for the reasons why.