popen2.Popen3() does not exist on Windows

[gotoh@…]

On windows python 2.3 does not have popen2.Popen3(), so plugin cannot invoke graphviz commands. For temporary workaround, I'm using following patch but is not correct fix because it cannot handle exit code.

graphviz/graphviz.py

@@ -344 +344 @@
 
     def launch(self, cmd, input):
         """Launch a process (cmd), and returns exitcode, stdout + stderr"""
-        p = popen2.Popen3(cmd, capturestderr=1)
+        p = popen2.popen3(cmd)
         if input:
-            p.tochild.writelines(input)
-        p.tochild.close()
-        out = p.fromchild.read()
-        err = p.childerr.read()
-        ret = p.wait()
-        if os.name == "posix":
-            ret = ret >> 8
+            p[1].writelines(input)
+        p[1].close()
+        out = p[0].read()
+        err = p[2].read()
+    ret = 0;
         return ret, out, err
 
 

[anonymous]

Fixed in v0.5 release.

[kilian]

Just a quick comment on Peter's fix in v0.5 : currently rsvg is kind enough to not display anything on stdout if no error occured, but that's not the case of otherpotential rasterizers, such as inkscape, which is verbose by default, even on success. So I guess checking len(stdout) could lead to false errors if rsvg output policy changes. Is there really no way to check exit codes under Windows?

[Peter Kropf]

Oh yeah, no doubt, this is not a great way of determining if a subprocess was successful. However, it works. At least for now ;-)

The most obvious way that I see to make things better is to create a platform specific launch methods. On Unix, it behaves as the previous version using popen2.Popen3. On windows it would use win32process. This means that there would be an additional requirement for GraphvizPlugin, the win32 extensions.

Another possibility is to use the process module from ​http://starship.python.net/crew/tmick/. But I don't have much experience with it.

Regardless, I'm open to suggestions for making the code more robust...

[Alec Thomas]

Would ​win32pipe be usable for this?

[Peter Kropf]

The Graphviz v0.7.x code now uses the subprocess module to run and communicate with the Graphviz programs.