By using this site, you agree to our updated Privacy Policy and our Terms of Use. Manage your Cookies Settings.
443,718 Members | 1,840 Online
Bytes IT Community
+ Ask a Question
Need help? Post your question and get tips & solutions from a community of 443,718 IT Pros & Developers. It's quick & easy.

writing serial port data to the gzip file

P: n/a
I am trying to save data it is comming from the serial port continually
for some period.
(expect reading from serial port is 100% not a problem)
Following is an example of the code I am trying to write. It works, but
it produce an empty gz file (0kB size) even I am sure I am getting data
from the serial port. It looks like g.close() does not close the gz
file.
I was reading in the doc:

Calling a GzipFile object's close() method does not close fileobj,
since you might wish to append more material after the compressed
data...

so I am completely lost now...

thanks for your comments.
Petr Jakes
==== snippet of the code ====
def dataOnSerialPort():
data=s.readLine()
if data:
return data
else:
return 0

while 1:
g=gzip.GzipFile("/root/foofile.gz","w")
while dataOnSerialPort():
g.write(data)
else: g.close()

Dec 18 '06 #1
Share this Question
Share on Google+
4 Replies


P: n/a

Petr Jakes wrote:
I am trying to save data it is comming from the serial port continually
for some period.
(expect reading from serial port is 100% not a problem)
Following is an example of the code I am trying to write. It works, but
it produce an empty gz file (0kB size) even I am sure I am getting data
from the serial port. It looks like g.close() does not close the gz
file.
I was reading in the doc:

Calling a GzipFile object's close() method does not close fileobj,
since you might wish to append more material after the compressed
data...

so I am completely lost now...

thanks for your comments.
Petr Jakes
==== snippet of the code ====
def dataOnSerialPort():
data=s.readLine()
if data:
return data
else:
return 0

while 1:
g=gzip.GzipFile("/root/foofile.gz","w")
while dataOnSerialPort():
g.write(data)
else: g.close()
Your while loop is discarding result of dataOnSerialPort, so you're
probably writing empty string to the file many times. Typically this
kind of loop are implemented using iterators. Check if your s object
(is it from external library?) already implements iterator. If it does
then

for data in s:
g.write(data)

is all you need. If it doesn't, you can use iter to create iterator for
you:

for data in iter(s.readLine, ''):
g.write(data)

-- Leo

Dec 18 '06 #2

P: n/a

If someone hasn't already commented,

Aside from any other problems, the file you are
trying to write to is (opened)?? in the "w" mode.
Every time a file is opened in the 'w' mode,
everything in the file is deleted.

If you open a file in the 'a' mode, then
everything in the file is left untouched and the
new data is appended to the end of the file.

Your while loop is deleting everything in the file
on each loop with the 'w' mode.

try,
vfile = open('vfile', 'a')
rather than
vfile = open('vfile', 'w')

jim-on-linux
http:\\www.inqvista.com

while 1:
g=gzip.GzipFile("/root/foofile.gz","w")
while dataOnSerialPort():
g.write(data)
else: g.close()


On Sunday 17 December 2006 20:06, Petr Jakes
wrote:
I am trying to save data it is comming from the
serial port continually for some period.
(expect reading from serial port is 100% not a
problem) Following is an example of the code I
am trying to write. It works, but it produce an
empty gz file (0kB size) even I am sure I am
getting data from the serial port. It looks
like g.close() does not close the gz file.
I was reading in the doc:

Calling a GzipFile object's close() method does
not close fileobj, since you might wish to
append more material after the compressed
data...

so I am completely lost now...

thanks for your comments.
Petr Jakes
==== snippet of the code ====
def dataOnSerialPort():
data=s.readLine()
if data:
return data
else:
return 0

while 1:
g=gzip.GzipFile("/root/foofile.gz","w")
while dataOnSerialPort():
g.write(data)
else: g.close()
Dec 18 '06 #3

P: n/a
Maybe I am missing something. Expect data is comming continually to the
serial port for the period say 10min. (say form the GPS), than it stops
for 1 minute and so on over and over. I would like to log such a data
to the different gzip files.
My example was written just for the simplicity (I was trying to
demonstrate the problem, it was not the real code and I was really
tired trying to solve it by myself, sorry for the bugy example)

the better way how to write such a infinite loop can be probably:
===== 8< =====
g=0
x=0
while 1:
if not g:
x+=1
g=gzip.GzipFile("/root/foofile%s.gz" % x,"w")
data=dataOnSerialPort()
while data:
myFlag=1
g.write(data)
data=dataOnSerialPort():
else:
if myFlag:
g.close()
pring g
myFlag=0

But it looks like g.close() method does not close the file (while
trying to print the g object, it still exists)

Your while loop is discarding result of dataOnSerialPort, so you're
probably writing empty string to the file many times. Typically this
kind of loop are implemented using iterators. Check if your s object
(is it from external library?) already implements iterator. If it does
then

for data in s:
g.write(data)

is all you need. If it doesn't, you can use iter to create iterator for
you:

for data in iter(s.readLine, ''):
g.write(data)

-- Leo
Dec 18 '06 #4

P: n/a
Hi Dennis,
thanks for your reply.
Dennis Lee Bieber napsal:
def dataOnSerialPort():
data=s.readLine()

Unless you are using a custom serial port module, that should be
s.readline()
sorry for the typo
>
if data:
return data
else:
return 0

This if statement is meaningless -- if "data" evaluates to false,
return a numeric value that evaluates to false.
I see, it is OK just to return data (or an empty string "")
>

while 1:
g=gzip.GzipFile("/root/foofile.gz","w")
while dataOnSerialPort():
g.write(data)

"data" is an uninitialized value here
else: g.close()

And what is the purpose of closing the file if you immediately turn
around and create it again (assuming gzip.GzipFile() behaves as open()
does, a mode of "w" means delete the old file and create a new one.
There is NO exit from the above.

Since I can't read your mind with regards to some of your looping...

s = ... #somewhere you had to open the serial port

g = gzip.GzipFile("/root/foofile.gz", "w")
while True:
data = s.readline()
if not data: break
g.write(data)
g.close()
what I am trying to say is g.close() does not close the g file (try to
add the line "print g" after g.close())
Petr

Dec 18 '06 #5

This discussion thread is closed

Replies have been disabled for this discussion.