Why changing signals causes NameErrors in a sane code? - PyGtk issue

Question

I'm working on a very simple app for Ubuntu. I've asked a question on stackoverflow, and it seems that the issue I am having is caused by signals, not by the scope of variables, as I originally thought. The problem I am having is that when TextBox emits a signal through activate the whole code works without a glitch. But when I change the signal to insert-at-click it returns NameErrors in every non-TextBox-linked function. Now, It is highly possible I am doing something completely wrong here, but is it at least probable that signals could affect global variable assignments?

The code in its current form giving me NameErrors:

def on_servername_insertatcursor(self, widget):
global output  
output = StringIO.StringIO()         
servername = widget.get_text()
output.write("USHARE_NAME="+servername+'\n')

def on_netif_changed(self, widget):
netif = widget.get_active_text()
global output
output.write("USHARE_IFACE="+netif+'\n')

def on_port_insertatcursor(self, widget):
global output
port = widget.get_text()
output.write("USHARE_PORT="+port+'\n')

def on_telprt_insertatcursor(self, widget):
global output
telprt = widget.get_text()
output.write("USHARE_TELNET_PORT="+telprt+'\n')

def on_dirs_insertatcursor(self, widget):
global output
dirs = widget.get_text()
output.write("USHARE_DIR="+dirs+'\n')

def on_iconv_toggled(self, widget):
global output
iconv = widget.get_active()
if iconv == True:
    output.write("USHARE_OVERRIDE_ICONV_ERR="+"True"+'\n')
else:
    output.write("USHARE_OVERRIDE_ICONV_ERR="+"False"+'\n')

def on_webif_toggled(self, widget):
global output
webif = widget.get_active()
if webif == True:
    output.write("USHARE_ENABLE_WEB="+"yes"+'\n')
else:
    output.write("USHARE_ENABLE_WEB="+"no"+'\n')

def on_telif_toggled(self, widget):
global output
telif = widget.get_active()
if telif == True:
    output.write("USHARE_ENABLE_TELNET="+"yes"+'\n')
else:
    output.write("USHARE_ENABLE_TELNET="+"no"+'\n')

def on_xbox_toggled(self, widget):
global output
xbox = widget.get_active()
if xbox == True:
    output.write("USHARE_ENABLE_XBOX="+"yes"+'\n')
else:
    output.write("USHARE_ENABLE_XBOX="+"no"+'\n')

def on_dlna_toggled(self, widget):
global output
dlna = widget.get_active()
if dlna == True:
    output.write("USHARE_ENABLE_DLNA="+"yes"+'\n')
else:
    output.write("USHARE_ENABLE_DLNA="+"no"+'\n')

def on_commit_clicked(self, widget):
commit = output.getvalue()
logfile = open('/home/boywithaxe/Desktop/ushare.conf','w')
logfile.write(commit)

def on_endprogram_clicked(self, widget):
sys.exit(0)

Answer 1

You're misunderstanding the meaning of the global statement in Python. Here's what the Python documentation says:

The global statement ... means that the listed identifiers are to be interpreted as globals. It would be impossible to assign to a global variable without global, although free variables may refer to globals without being declared global.

So, basically, you only need to use global blah when you need to assign to a global variable called blah. The variable, however, should already exist in the global scope. If you're just accessing a global variable or its methods (as apposied to assigning to it), you don't need to declare it as global.

So what you need is something like

output = None

def on_servername_insertatcursor(self, widget):
    global output  
    output = StringIO.StringIO()         
    servername = widget.get_text()
    output.write("USHARE_NAME="+servername+'\n')

def on_netif_changed(self, widget):
    netif = widget.get_active_text()
    output.write("USHARE_IFACE="+netif+'\n')

...

However, the whole approach with using a global variable and making the whole thing dependent on the order of function calls (on_servername_insertatcursor MUST be called first, otherwise the other functions will fail) is not a good coding practice.

UPDATE: Also, it occurred to me that the functions you're showing are in fact methods of a class, is that right? In this case, you can make output a member of the class and access it as self.output:

class MyApp(gtk.Window):

    output = None

    def __init__(...):
        ...
        self.output = StringIO.StringIO()

    def on_servername_insertatcursor(self, widget):    
        servername = widget.get_text()
        self.output.write("USHARE_NAME="+servername+'\n')

    def on_netif_changed(self, widget):
        netif = widget.get_active_text()
        self.output.write("USHARE_IFACE="+netif+'\n')

Still, the output of your app is dependent on the order user clicks the buttons, which is not cool. For example if user clicks the "dlna" checkbox twice, there will be 2 lines in the config, which I presume is not what you want.