[MATRIX-SIG] namespaces, constructors, and global variables

[Phil Austin]

The following message is a courtesy copy of an article
that has been posted as well.


We're working on a generic plotting interface to gnuplot, gist, ncar
graphics, etc., and are currently stumped by our lack of understanding
of namespaces.  The interface puts a plot together by creating a
series of objects (plots, axes, ticks, legends, etc.) with methods to
add or modify fonts, colors, line widths, whatever.  The state of the
plot is stored in a global dictionary, and an execute method goes
through the dictionary and builds the plot for the appropriate
software package.  An example:


>>> from PlotAll import *
>>> plotIt=PlotDriver(device="screen")
>>> plot1=BuildPlot(time, xarray)
>>> leftAxis=BuildAxis(plot1,axis="left",label="xarray")
>>> print Master['plot1']['leftAxis']['label']
xarray


Our problem is that we would like a botAxis and a leftAxis object to
be created by default when a plot object is instantiated without the
argument "axes=False".  I'm appending a version of PlotAll.py, which
does this without a hitch from within the interpreter:

>>> import PlotAll
>>> PlotAll.runit()
Master.keys():  ['plotCount', 'device', 'plot1']
inside BuildAxis: Master.keys()= ['plotCount', 'device', 'plot1']
inside BuildAxis: Master.keys()= ['plotCount', 'device', 'plot1']
Bottom: Master['plot1']['leftAxis']['label']= ytest
>>> leftAxis
<BuildAxis instance at 820e290>


Running from the shell, however, doesn't work, because the global
variable Master doesn't appear to have it's keys:

<phil@curlew: src.dir/python.dir> python PlotAll.py
Master.keys():  ['plotCount', 'device', 'plot1']
inside BuildAxis: Master.keys()= []

Can someone walk me through why this is failing, and how I can fix it?

Thanks, Phil

______________________________PlotAll.py_______________________________

Master={}
global Master

class PlotDriver:
    global Master
    def __init__(self,device="postscript"):
	self.RCSId="$Id: PlotAll.py,v 1.5 1997/07/09 16:31:05 phil Exp $"
        Master['plotCount']=0
        Master['device']=device


class BuildPlot:
    global Master
    def __init__(self,xdata,ydata,plotType="linePlot",axes="default"):
	Master['plotCount'] = Master['plotCount'] + 1
	self.plotName="plot%d" % Master['plotCount']
        Master[self.plotName]={}
        Master[self.plotName]['xdata']=xdata
	Master[self.plotName]['ydata']=ydata
	Master[self.plotName]['plotType']=plotType
	if(axes=="default"):
	    import __main__
	    plot=self
	    global Master
	    ns=vars()
	    print "Master.keys(): ", Master.keys()
	    code=["from PlotAll import *",
		  "global Master",
		  "leftAxis=BuildAxis(plot,axis=\"left\",label=\"ytest\")",    
		  "botAxis=BuildAxis(plot,axis=\"bot\",label=\"x\")"]
	    for stmt in code:
		exec stmt in ns,__main__.__dict__
	

class BuildAxis:
    global Master
    def __init__(self,Plot,axis="left",label="default",limit="default"):
	global Master
        print "inside BuildAxis: Master.keys()=", Master.keys()
	self.plotName=Plot.plotName
	self.axisName="%sAxis" % axis
        Master[self.plotName][self.axisName]={}
	Master[self.plotName][self.axisName]['label']=label
	Master[self.plotName][self.axisName]['limit']=limit

def runit():
    global Master
    xarray=[1,2,3,4]
    time=[5,6,7,8]

#controls items common to all plots
    plotIt=PlotDriver(device="screen")

#build an individual plot
    plot=BuildPlot(time, xarray)
    print "Bottom: Master['plot1']['leftAxis']['label']=", Master['plot1']['leftAxis']['label']


if __name__ == "__main__":runit()

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