python gnuplot.plot 命令在字符串输入时失败

Question

在gnuplot的命令行中，你可以这样做：

gnuplot> plot "fileA.dat" using 1:2 title 'data A', \ "fileB.dat" using 1:3 title 'data B'

使用python的gnuplot.py时，下面这个函数可以正常工作：

def create_plot():
   ...
   for target in TARGET_LIST:
        for protocol in PROTOCOL_LIST:

            input_file_name = "%s/%s.db" % (DATA_DIR, target)
            shortname = input_file_name.split('/')[-1]
            shortname = shortname.rstrip('.db')

            input_list = read_lines(input_file_name)

            write_plot_file_name = '%s/%s.%s.write.out' % (DATA_DIR, shortname, protocol)
            write_plot_file = open(write_plot_file_name, 'w')

            read_plot_file_name = '%s/%s.%s.read.out' % (DATA_DIR, shortname, protocol)
            read_plot_file = open(read_plot_file_name, 'w')

            ping_plot_file_name = '%s/%s.ping.out' % (DATA_DIR, shortname)
            ping_plot_file = open(ping_plot_file_name, 'w')

            for line in input_list[ limit: ]:

                line = line.rstrip("\n")
                line_protocol, line_verb, delta, timestamp = line.split('|')

                if line_protocol == protocol:
                    if line_verb == 'write':
                        write_plot_file.write("%s,%s\n" % (timestamp, delta))
                    else:
                        read_plot_file.write("%s,%s\n" % (timestamp, delta))
                elif line_protocol == 'ping':
                    ping_plot_file.write("%s,%s\n" % (timestamp, delta))

            #gnuplot stuff

            png_file = "%s/%s.%s.png" % (PLOT_DIR, shortname, protocol)

            title = '%s history for %s ' % (protocol, shortname)

            gnuplot = Gnuplot.Gnuplot()
            gnuplot.title(title)
            gnuplot('set style data linespoints')
            gnuplot('set ylabel "seconds"')
            gnuplot('set xlabel "month:day:hour:minute:seconds:millisecond"')
            gnuplot('set xdata time')
            gnuplot('set timefmt "%s"')
            gnuplot('set format x "%m:%d:%H:%M:%S:%MS"')
            gnuplot('set xtics nomirror rotate by -90')
            gnuplot('set datafile separator ","')
            gnuplot('set autoscale')
            gnuplot('set grid xtics ytics')
            gnuplot('set terminal png size 900,899')
            gnuplot('set output "%s"' % (png_file))

            cmd = ' "%s"  using 1:2 axes x1y1 title "write" with lines, \
                   "%s"  using 1:2 axes x1y1 title "read" with lines, \
                   "%s"  using 1:2 axes x1y2 title "ping" with lines' % \
                   (write_plot_file_name, read_plot_file_name, ping_plot_file_name)

            try:
                gnuplot.plot(cmd)
            except Error as why:
                print "gnuplot choked: %s" % (why)

但是，当我按照python的方式把这个分成两个函数时：


def read_data(): #做上面相同的文件/数据处理

png_file = "%s/%s.%s.png" % (PLOT_DIR, shortname, protocol)

title = '%s history for %s ' % (protocol, shortname)

cmd = ' "%s"  using 1:2 axes x1y1 title "write" with lines, \
    "%s"  using 1:2 axes x1y1 title "read" with lines, \
    "%s"  using 1:2 axes x1y2 title "ping" with lines' % \
    (write_plot_file_name, read_plot_file_name, ping_plot_file_name)

def create_plot(png_file, title, cmd):
#call the gnuplot 'set' strings as above 
gnuplot = Gnuplot.Gnuplot()
gnuplot.title(title)
gnuplot('set style data linespoints')
gnuplot('set ylabel "seconds"')
gnuplot('set xlabel "month:day:hour:minute:seconds:millisecond"')
gnuplot('set xdata time')
gnuplot('set timefmt "%s"')
gnuplot('set format x "%m:%d:%H:%M:%S:%MS"')
gnuplot('set xtics nomirror rotate by -90')
gnuplot('set datafile separator ","')
gnuplot('set autoscale')
gnuplot('set grid xtics ytics')
gnuplot('set terminal png size 900,899')
gnuplot('set output "%s"' % (png_file))`) 

然后调用gnuplot.plot(cmd)时，这就出现了各种各样的问题，显然是因为gnuplot试图把字符串本身绘制出来，而不是像第一种情况那样进行解析。

这是怎么回事呢？有没有什么解决办法？

Answer 1

明白了：

这两个函数都没有关闭文件（这不好！不好！），在单个函数内部这样做是可以的——文件描述符仍然有效。

当

write_plot_file.close()
read_plot_file.close()
ping_plot_file.close()

被包含在 read_data() 中时，一切都会变得更好。