Hi All,
i'm tring to use grass modules that needs a "standard input" method,
like "m.proj"
here an example where i'musing a "file" as input :
coords = read_command('m.proj', input=coordsfile, flags='i')
how to use standard input, like in bash :
echo '599537.80 4920995.38' | m.proj -o
there is a python way to do it, or i need to use "system call" like os.system or subprocess ?
thanks!
Massimo.
Massimo Di Stefano wrote:
i'm tring to use grass modules that needs a "standard input" method,
like "m.proj"
here an example where i'musing a "file" as input :
coords = read_command('m.proj', input=coordsfile, flags='i')
how to use standard input, like in bash :
echo '599537.80 4920995.38' | m.proj -o
there is a python way to do it, or i need to use "system call" like
os.system or subprocess ?
If you want to read from the child's stdout, there's pipe_command()
and read_command(). If you want to write to the child's stdin, there's
feed_command() and write_command().
If you want to do both, you need to do it yourself using
start_command() (on which the other functions are based), e.g.:
import grass.script as grass
def read_write_command(*args, **kwargs):
input = kwargs['stdin']
kwargs['stdout'] = grass.PIPE
kwargs['stdin'] = grass.PIPE
ps = grass.start_command(*args, **kwargs)
return ps.communicate(input)[0]
This behaves like a combination of read_command() and write_command().
The input string is passed via the "stdin" parameter as for
write_command(), while the data from the child's stdout is returned as
for read_command().
If you want a pipe_command/feed_command interface with file handles,
it gets problematic. You need to use non-blocking I/O or multiple
threads; otherwise, you can get deadlock, with the child blocked
waiting for the parent to read the child's stdout while the parent is
blocked writing to the child's stdin.
If you really need this, look at the implementation of
subprocess.communicate(); the Unix version uses select() while Windows
uses threads.
Alternatively, redirect the child's stdout to a file and have the
parent read the file; writing to a file never blocks.
BTW, if you need even lower-level access, use grass.Popen() or
grass.call(). These are almost identical to subprocess.Popen() and
subprocess.call() except that, on Windows, they set shell=True by
default. This allows commands to be either scripts or binary
executables, and doesn't require the extension; with shell=False, the
command must be a binary executable and must include the ".exe"
suffix.
--
Glynn Clements <glynn@gclements.plus.com>
Hi Glynn,
thanks for your help!
actually i'm using :
out = subprocess.Popen(['m.proj', '-o'], stdout=subprocess.PIPE, stdin=subprocess.PIPE).communicate("%s %s" % (x,y))[0]
reading the code you point me, looks similar.
for now i only need to convert to lon-lat the point-position "picked" by the mouse on the map-canvas
(it is a short action so i can avoid to use thread).
in the next days i have to write a v.in.asci based code that read data from standard-input (a serial port connection) ... the thread problem will come.
Glynn, List,
This topic, maybe is good to discuss a problem i'm having about subprocess,
please apologize me if it is OT, tell me to open a new thread.
The error i'm having is strictly connected with subprocess and how grass handle it.
The weird is that the error i'm having comes up only on OSX while on linux all works fine.
this the error log :
GRASS 6.5.svn (spearfish60):~ > python2.6 /Users/sasha/Desktop/OssimPlanetSasha/try.py
Traceback (most recent call last):
File "/Users/sasha/Desktop/OssimPlanetSasha/try.py", line 1765, in <module>
p.init()
File "/Users/sasha/Desktop/OssimPlanetSasha/try.py", line 75, in init
self.DataW = DataWork()
File "/Users/sasha/Desktop/OssimPlanetSasha/datatools.py", line 37, in __init__
self.vector = self.VectorList()
File "/Users/sasha/Desktop/OssimPlanetSasha/datatools.py", line 543, in VectorList
v = list_strings('vect')
File "/Applications/GRASS-6.5.app/Contents/MacOS/etc/python/grass/script/core.py", line 636, in list_strings
return ["%s@%s" % pair for pair in list_pairs(type)]
File "/Applications/GRASS-6.5.app/Contents/MacOS/etc/python/grass/script/core.py", line 621, in list_pairs
for mapset, maps in list_grouped(type).iteritems()])
File "/Applications/GRASS-6.5.app/Contents/MacOS/etc/python/grass/script/core.py", line 562, in list_grouped
for line in read_command("g.list", type = type).splitlines():
File "/Applications/GRASS-6.5.app/Contents/MacOS/etc/python/grass/script/core.py", line 210, in read_command
return ps.communicate()[0]
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 663, in communicate
stdout = self.stdout.read()
IOError: [Errno 4] Interrupted system call
GRASS 6.5.svn (spearfish60):~ >
the line that generate the error is :
v = list_strings('vect')
if i comment out all the related code, the error comes up in other lines that use the grass-python code.
like :
s = read_command("g.region", flags='l')
or
units = read_command("g.proj", flags='p')
it is a "random error" 
important note :
the error come up "ever" if i have Ossimplanet already open and running
if i quit it and try again, the % of the error are drastically reduced to 1 : 10 , (every 10 times i start the application , i have 1 error)
the error easly comes up also when more application are opened on my laptop and more intense is the cpu usage.
Sinverly i have no clue,
probably it can depends by a (my) bad programming skill.
PlanetSasha hat too many lines and files .. so i is hard to be used as debug code
i'll try to set up a little script to replicate the problem.
thanks!
Massimo.
Il giorno 28/apr/2010, alle ore 23.16, Glynn Clements ha scritto:
Massimo Di Stefano wrote:
i'm tring to use grass modules that needs a "standard input" method,
like "m.proj"
here an example where i'musing a "file" as input :
coords = read_command('m.proj', input=coordsfile, flags='i')
how to use standard input, like in bash :
echo '599537.80 4920995.38' | m.proj -o
there is a python way to do it, or i need to use "system call" like
os.system or subprocess ?If you want to read from the child's stdout, there's pipe_command()
and read_command(). If you want to write to the child's stdin, there's
feed_command() and write_command().If you want to do both, you need to do it yourself using
start_command() (on which the other functions are based), e.g.:import grass.script as grass
def read_write_command(*args, **kwargs):
input = kwargs['stdin']
kwargs['stdout'] = grass.PIPE
kwargs['stdin'] = grass.PIPE
ps = grass.start_command(*args, **kwargs)
return ps.communicate(input)[0]This behaves like a combination of read_command() and write_command().
The input string is passed via the "stdin" parameter as for
write_command(), while the data from the child's stdout is returned as
for read_command().If you want a pipe_command/feed_command interface with file handles,
it gets problematic. You need to use non-blocking I/O or multiple
threads; otherwise, you can get deadlock, with the child blocked
waiting for the parent to read the child's stdout while the parent is
blocked writing to the child's stdin.If you really need this, look at the implementation of
subprocess.communicate(); the Unix version uses select() while Windows
uses threads.Alternatively, redirect the child's stdout to a file and have the
parent read the file; writing to a file never blocks.BTW, if you need even lower-level access, use grass.Popen() or
grass.call(). These are almost identical to subprocess.Popen() and
subprocess.call() except that, on Windows, they set shell=True by
default. This allows commands to be either scripts or binary
executables, and doesn't require the extension; with shell=False, the
command must be a binary executable and must include the ".exe"
suffix.--
Glynn Clements <glynn@gclements.plus.com>
Massimo Di Stefano wrote:
actually i'm using :
out = subprocess.Popen(['m.proj', '-o'], stdout=subprocess.PIPE, stdin=subprocess.PIPE).communicate("%s %s" % (x,y))[0]
That will work on Unix, but Windows will complain due to the lack of
the .exe suffix. You can use grass.Popen() to get around that.
This topic, maybe is good to discuss a problem i'm having about subprocess,
please apologize me if it is OT, tell me to open a new thread.The error i'm having is strictly connected with subprocess and how grass handle it.
The weird is that the error i'm having comes up only on OSX while on linux all works fine.this the error log :
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 663, in communicate
stdout = self.stdout.read()
IOError: [Errno 4] Interrupted system call
This appears to be a bug either in Python's read() method for pipes or
in Python's subprocess module. The underlying read() is failing with
EINTR, which can happen if a signal is received during a blocking
system call.
Normally, you would configure the signal handler to resume any system
calls (unless you specifically want it to interrupt blocking calls,
e.g. implementing a timeout by setting a timer and having SIGALRM
interrupt the system call).
In this case, I would expect the code to just try again, rather than
raising an exception. EINTR and EAGAIN are "transient" errors, in that
a subsequent attempt will typically succeed.
--
Glynn Clements <glynn@gclements.plus.com>
Il giorno 30/apr/2010, alle ore 02.39, Glynn Clements ha scritto:
Massimo Di Stefano wrote:
actually i'm using :
out = subprocess.Popen(['m.proj', '-o'], stdout=subprocess.PIPE, stdin=subprocess.PIPE).communicate("%s %s" % (x,y))[0]
That will work on Unix, but Windows will complain due to the lack of
the .exe suffix. You can use grass.Popen() to get around that.
thanks Glynn i adopted this way and it works (but i haven't tested on windows)
This topic, maybe is good to discuss a problem i'm having about subprocess,
please apologize me if it is OT, tell me to open a new thread.The error i'm having is strictly connected with subprocess and how grass handle it.
The weird is that the error i'm having comes up only on OSX while on linux all works fine.this the error log :
File "/System/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/subprocess.py", line 663, in communicate
stdout = self.stdout.read()
IOError: [Errno 4] Interrupted system callThis appears to be a bug either in Python's read() method for pipes or
in Python's subprocess module. The underlying read() is failing with
EINTR, which can happen if a signal is received during a blocking
system call.Normally, you would configure the signal handler to resume any system
calls (unless you specifically want it to interrupt blocking calls,
e.g. implementing a timeout by setting a timer and having SIGALRM
interrupt the system call).In this case, I would expect the code to just try again, rather than
raising an exception. EINTR and EAGAIN are "transient" errors, in that
a subsequent attempt will typically succeed.
i'm tring to find a way to follow your suggestions.
if "function()" is the subprocess action that give me error on osx
maybe i can try something like :
while 1:
try:
function()
break
except IOError:
sleep(0.1)
--
Glynn Clements <glynn@gclements.plus.com>