On 10/4/2017 1:24 PM, Grant Edwards wrote:
On 2017-10-04, Steve D'Aprano <steve+pyt...@pearwood.info> wrote:
It is sometimes called the loop and a half problem. The idea is
that you must attempt to read a line from the file before you know
whether you are at the end of file or not.
Utter nonsense. There's no "must" here. I'll accept the remote
possibility that maybe one time in a million you have to do what he
says, but the other 999999 times you just read from the file in a
for-loop:
for line in file:
process(line)
This can also be done if a boolean variable is introduced to help
with the while loop. This boolean variable is the condition that
gets you out of the while loop and the first time through it must be
set to get your code to execute the while loop at least one."
I've been programming in Python for twenty years, and I don't think I have
ever once read from a file using a while loop.
You're right, that construct isn't used for reading from files in
Python. It _is_ commonly used for reading from things like socket
mysock.connect(...)
while True:
data = mysock.recv(9999)
if not data:
break
do_something_with(data)
mysock.close()
I contend that it would be better in this case also to separate data
access from data processing.
def sockreader(socket, size):
while True:
data = socket.recv(size)
if data:
yield data
else:
break
for data in socketreader(mysock, 9999):
do_something_with(data)
Perhaps the socket module needs an update to make the boilerplate
generator function a method, such as 'iterread'.
The separation lets one write source-agnostic processing functions.
def do_something(source):
for data in source:
<code that implements 'do-something'>
One can now 'do_something' with data from pipe, file, socket, or list.
--
Terry Jan Reedy
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