Get a variable from gnuplot #12
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pi = gp.get('pi')
Returns a string
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Thank you very much for the contribution! The problem comes with the "Popen.communicate()" function, as it terminates the pipe after usage: https://stackoverflow.com/questions/25754045/python-subprocess-i-o-operation-on-closed-file |
Oh, I'm sorry, I hurried. import sys
from subprocess import PIPE, Popen
from threading import Thread
try:
from queue import Queue, Empty
except ImportError:
from Queue import Queue, Empty # python 2.x
ON_POSIX = 'posix' in sys.builtin_module_names
def enqueue_std(out, queue):
for line in iter(out.readline, ''):
queue.put(line)
out.close()
class Gnuplot(object):
"""docstring for Gnuplot"""
def __init__(self):
self.p = Popen(['gnuplot', '-p'], stdin=PIPE, stderr=PIPE, stdout=PIPE, bufsize=1,
close_fds=ON_POSIX, shell=False, universal_newlines=True)
self.q_err = Queue()
self.t_err = Thread(target=enqueue_std, args=(self.p.stderr, self.q_err))
self.t_err.daemon = True # thread dies with the program
self.t_err.start()
self.q_out = Queue()
self.t_out = Thread(target=enqueue_std, args=(self.p.stdout, self.q_out))
self.t_out.daemon = True # thread dies with the program
self.t_out.start()
def c(self, command):
self.p.stdin.write(command + '\n') # \n 'send return in python 2.7'
self.p.stdin.flush() # send the command in python 3.4+
def get(self, variable, timeout=0.1):
self.p.stdin.write('print ' + variable + '\n')
# read line without blocking
try:
line = self.q_err.get(timeout=timeout) # or .get_nowait()
return line
except Empty:
return NoneUse library: #!/usr/bin/env python3
from gnuplot import Gnuplot as gp
figure1 = gp()
figure1.c('set terminal postscript eps color enhanced "Helvetica" 30')
figure1.c('set output "%s"' % 'result.ps')
figure1.c('set size 1.25,1.33')
figure1.c('set pointsize 2')
figure1.c('set nokey')
figure1.c('set linestyle 1 linetype -1 linewidth 1')
figure1.c('set xlabel "Detector"')
figure1.c('set ylabel "Calibration Quantity"')
figure1.c('set title "Title"')
figure1.c('plot sin(x)')
my_pi = figure1.get('pi')
print(my_pi)And: |
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Thanks again, This is a good find, and seems to work. In fact, the communicate function also seems use a thread for the readout I will experiment with the options a little and see what works best. |
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I will use your suggested code since it is very clean and works very well! |
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I made small edits. import sys
from subprocess import PIPE, Popen
from threading import Thread
try:
from queue import Queue, Empty
except ImportError:
from Queue import Queue, Empty # python 2.x
ON_POSIX = 'posix' in sys.builtin_module_names
class Gnuplot(object):
"""docstring for Gnuplot"""
def __init__(self):
self.p = Popen(['gnuplot', '-p'], stdin=PIPE, stderr=PIPE, stdout=PIPE, bufsize=1,
close_fds=ON_POSIX, shell=False, universal_newlines=True)
self.q_err = Queue()
self.t_err = Thread(target=self.enqueue_std, args=(self.p.stderr, self.q_err))
self.t_err.daemon = True # thread dies with the program
self.t_err.start()
self.q_out = Queue()
self.t_out = Thread(target=self.enqueue_std, args=(self.p.stdout, self.q_out))
self.t_out.daemon = True # thread dies with the program
self.t_out.start()
def enqueue_std(self, out, queue):
for line in iter(out.readline, ''):
queue.put(line)
out.close()
def c(self, command):
self.p.stdin.write(command + '\n') # \n 'send return in python 2.7'
self.p.stdin.flush() # send the command in python 3.4+
def get_c(self, vtype=str, timeout=0.1):
# read line without blocking
lines = []
while True:
try:
line = self.q_err.get(timeout=timeout) # or .get_nowait()
lines.append(vtype(line.strip()))
except Empty:
break
return lines
def get(self, variable, vtype=float, timeout=0.1):
# clean buffer before put command
self.get_c()
self.p.stdin.write('print ' + variable + '\n')
# read line without blocking
try:
line = self.q_err.get(timeout=timeout) # or .get_nowait()
return vtype(line.strip())
except Empty:
return Noneuse: #!/usr/bin/env python3
from gnuplot import Gnuplot as gp
figure1 = gp()
figure1.c('set terminal postscript eps color enhanced "Helvetica" 30')
figure1.c('set output "%s"' % 'result.ps')
figure1.c('set size 1.25,1.33')
figure1.c('set pointsize 2')
figure1.c('set nokey')
figure1.c('set linestyle 1 linetype -1 linewidth 1')
figure1.c('set xlabel "Detector"')
figure1.c('set ylabel "Calibration Quantity"')
figure1.c('set title "Title"')
figure1.c('set fit logfile "/dev/null"')
figure1.c('set fit quiet')
figure1.c('FIT_LIMIT = 1e-6')
figure1.c('f(x) = m*x**2 + b')
figure1.c('fit f(x) "calibration.data" using 1:2 via m, b')
figure1.c('plot "calibration.data" using 1:2, f(x) w l')
# !!! wrong command !!!
figure1.c('wrong command')
log = figure1.get_c()
print("\n".join(log))
m = figure1.get('m')
b = figure1.get('b')
m_err = figure1.get('m_err')
b_err = figure1.get('b_err')
print("m = {0}".format(m))
print("b = {0}".format(b))
print("m_err = {0}".format(m_err))
print("b_err = {0}".format(b_err))I do not know how to check the result of the execution of each command. The timeout is now used, since the execution of a command in gnuplot may take some time. If you check after each command, it will be very slow. |
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I also found it very strange: gnuplot does not use stdout. It sends the entire message (data output or error messages) to strerr! |
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Wow! Just need to read the documentation. To separate messages into errors and data, you need to say in the object's constructor: self.c('set print "-"') |
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Thats actually explains a lot, also why my earlier attempts to just read stdout failed. |
2 participants
Sometimes it is required to get the values of variables from gnuplot. For example after:
Now from Python you can access these variables.