python Process return global variable

Question

I open more Process with python to retrive files via urlib2, I only put the call to the fucntion.

t = Process(target=traer, args=(dir, listado[contador],))

This is the function that call in the process object

def traer(dir,y):
    global listado2
    try:
        file = urllib2.urlopen(dir+y)
        nombre=y
        output = open('C:/ndfd/degrib/bin/archivos/'+nombre ,'wb')
        output.write(file.read())
        output.close()
    except urllib2.HTTPError, e:
        print 'HTTPError = ' + str(e.code)
    except urllib2.URLError, e:
        listado2.append(y)
        print 'URLError = ' + str(e.reason)

This is in root of the archive

 if __name__ == '__main__':
     global listado
     global listado2
     listado=[]
     listado2=[]
     crear_trip(dir,listado)
     salida_bath(dir,listado,listado2)

inside salida_bath are inside a loop while that turn on the process.

In the exception I will like append to a global variable called listado2 but this not work, say me that it is undefined listado2.

MY FIX OF THIS PROBLEM FOR ME, change the strategy

create inside the salida_bath

    manager = Manager()
    listado2 = manager.dict()

put a contador of the process and past the new listado2 to the process

    t = Process(target=traer, args=(contador,dir, listado[contador],listado2))

and in traer function change this.

    except urllib2.URLError, e:
        listado2[contador]=y
        print 'URLError = ' + str(e.reason)

check outside that this is working

 for x in listado2.values():
      listado.append(x)
 print listado

lanzz · Accepted Answer · 2014-02-18 13:50:39Z

3

The global statement only informs the parser that the variable is not to be considered local, but it does not define a new variable if one does not exist. You're still responsible to initialize it somewhere before accessing it. You seem to assume it is a list (listado2.append(y)), but nowhere in your code you actually initialize it with a list value. How would Python know which .append() method to invoke on a variable that has never been assigned anything?

answered Feb 18, 2014 at 13:50

lanzz

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3 Comments

virtualsets Over a year ago

Hello, I initialize before call the process but outside. The process is calling in another function that initialize the global vars

lanzz Over a year ago

Then you should edit your question and include your code that shows how, where and when you initialize the listado2 variable.

virtualsets Over a year ago

Thank you for your time. I resolved, I dont know if it is bad or well, but this is working. ;) sorry myd bad english.

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