diff --git a/src/devede_ng.py b/src/devede_ng.py
index a43da01..6ed7bd5 100755
--- a/src/devede_ng.py
+++ b/src/devede_ng.py
@@ -30,7 +30,7 @@ import devedeng.choose_disc_type
 
 config_data = devedeng.configuration_data.configuration.get_config()
 
-if config_data == None:
+if config_data is None:
     print ("Can't locate extra files. Aborting.")
     sys.exit(1)
 
diff --git a/src/devedeng/add_files.py b/src/devedeng/add_files.py
index 119f069..fa7c410 100644
--- a/src/devedeng/add_files.py
+++ b/src/devedeng/add_files.py
@@ -36,7 +36,7 @@ class add_files:
         builder.connect_signals(self)
         wadd_files = builder.get_object("add_files")
         self.wfile_chooser = builder.get_object("filechooserwidget1")
-        if (add_files.last_path != None):
+        if (add_files.last_path is not None):
             self.wfile_chooser.set_current_folder(add_files.last_path)
         self.wbutton_accept = builder.get_object("button_accept")
 
diff --git a/src/devedeng/ask_subtitles.py b/src/devedeng/ask_subtitles.py
index 89d527d..b401158 100644
--- a/src/devedeng/ask_subtitles.py
+++ b/src/devedeng/ask_subtitles.py
@@ -41,7 +41,7 @@ class ask_subtitles:
         wencoding = builder.get_object("encoding_l")
         wlanguage = builder.get_object("language_l")
 
-        if (devedeng.add_files.add_files.last_path != None):
+        if (devedeng.add_files.add_files.last_path is not None):
             self.wfilename.set_current_folder(devedeng.add_files.add_files.last_path)
 
         lang_selection = 0
@@ -114,7 +114,7 @@ class ask_subtitles:
     def on_subtitle_file_set(self,b):
         
         f = self.wfilename.get_filename()
-        if (f == None) or (f == ""):
+        if (f is None) or (f == ""):
             self.waccept.set_sensitive(False)
         else:
-            self.waccept.set_sensitive(True)
\ No newline at end of file
+            self.waccept.set_sensitive(True)
diff --git a/src/devedeng/avprobe.py b/src/devedeng/avprobe.py
index 880fa88..80c716f 100644
--- a/src/devedeng/avprobe.py
+++ b/src/devedeng/avprobe.py
@@ -126,11 +126,11 @@ class avprobe(devedeng.avbase.avbase):
                     self.original_audiorate_uncompressed = int(float(element["sample_rate"]))
 
         self.original_size = str(self.original_width)+"x"+str(self.original_height)
-        if (self.original_aspect_ratio == None) or (self.original_aspect_ratio <= 1.0):
+        if (self.original_aspect_ratio is None) or (self.original_aspect_ratio <= 1.0):
             if (self.original_height != 0):
                 self.original_aspect_ratio = (float(self.original_width))/(float(self.original_height))
 
-        if (self.original_aspect_ratio != None):
+        if (self.original_aspect_ratio is not None):
             self.original_aspect_ratio = (float(int(self.original_aspect_ratio*1000.0)))/1000.0
 
         if (len(self.video_list) == 0):
diff --git a/src/devedeng/choose_disc_type.py b/src/devedeng/choose_disc_type.py
index 9e49db7..3819e47 100644
--- a/src/devedeng/choose_disc_type.py
+++ b/src/devedeng/choose_disc_type.py
@@ -43,7 +43,7 @@ class choose_disc_type(GObject.GObject):
         mkv = True
         analizers, players, converters, menuers, burners, mkiso = self.cv.get_needed_programs()
 
-        if (analizers != None) or (converters != None):
+        if (analizers is not None) or (converters is not None):
             dvd = False
             vcd = False
             cvd = False
@@ -51,10 +51,10 @@ class choose_disc_type(GObject.GObject):
             divx = False
             mkv = False
 
-        if menuers != None:
+        if menuers is not None:
             dvd = False
 
-        if mkiso != None:
+        if mkiso is not None:
             dvd = False
 
         if self.check_program(["dvdauthor","--help"]) == False:
diff --git a/src/devedeng/configuration_data.py b/src/devedeng/configuration_data.py
index 9a0090a..4c3620a 100644
--- a/src/devedeng/configuration_data.py
+++ b/src/devedeng/configuration_data.py
@@ -28,7 +28,7 @@ class configuration(GObject.GObject):
 
     @staticmethod
     def get_config():
-        if configuration.current_configuration == None:
+        if configuration.current_configuration is None:
             configuration.current_configuration = configuration()
             if (configuration.current_configuration.fill_config()):
                 configuration.current_configuration = None
@@ -59,14 +59,14 @@ class configuration(GObject.GObject):
         except:
             pass
 
-        if is_local == None:
+        if is_local is None:
             try:
                 os.stat("/usr/local/share/devede_ng/wselect_disk.ui")
                 is_local = True
             except:
                 pass
 
-        if is_local == None:
+        if is_local is None:
             return True
         else:
             if (is_local):
@@ -190,30 +190,30 @@ class configuration(GObject.GObject):
                 config_data.write("pal\n")
             else:
                 config_data.write("ntsc\n")
-            if (self.tmp_folder != None):
+            if (self.tmp_folder is not None):
                 config_data.write("temp_folder:"+str(self.tmp_folder)+"\n")
             config_data.write("multicore:"+str(self.multicore)+"\n")
-            if (self.final_folder != None):
+            if (self.final_folder is not None):
                 config_data.write("final_folder:"+str(self.final_folder)+"\n")
-            if (self.sub_language != None):
+            if (self.sub_language is not None):
                 config_data.write("sub_language:"+str(self.sub_language)+"\n")
-            if (self.sub_codepage != None):
+            if (self.sub_codepage is not None):
                 config_data.write("sub_codepage:"+str(self.sub_codepage)+"\n")
-            if (self.film_analizer != None):
+            if (self.film_analizer is not None):
                 config_data.write("film_analizer:"+str(self.film_analizer)+"\n")
-            if (self.film_player != None):
+            if (self.film_player is not None):
                 config_data.write("film_player:"+str(self.film_player)+"\n")
-            if (self.film_converter != None):
+            if (self.film_converter is not None):
                 config_data.write("film_converter:"+str(self.film_converter)+"\n")
-            if (self.menu_converter != None):
+            if (self.menu_converter is not None):
                 config_data.write("menu_converter:"+str(self.menu_converter)+"\n")
-            if self.burner != None:
+            if self.burner is not None:
                 config_data.write("burner:"+str(self.burner)+"\n")
-            if self.mkiso != None:
+            if self.mkiso is not None:
                 config_data.write("mkiso:"+str(self.mkiso)+"\n")
-            if (self.sub_codepage != None):
+            if (self.sub_codepage is not None):
                 config_data.write("sub_codepage:"+str(self.sub_codepage)+"\n")
-            if (self.sub_language != None):
+            if (self.sub_language is not None):
                 config_data.write("sub_language:"+str(self.sub_language)+"\n")
             config_data.write("subtitle_font_size:"+str(self.subtitles_font_size)+"\n")
             config_data.write("subtitle_fill_color:"+str(self.subt_fill_color[0])+","+str(self.subt_fill_color[1])+","+str(self.subt_fill_color[2])+"\n")
diff --git a/src/devedeng/converter.py b/src/devedeng/converter.py
index 6745463..ec1ea09 100644
--- a/src/devedeng/converter.py
+++ b/src/devedeng/converter.py
@@ -34,7 +34,7 @@ class converter:
 
     @staticmethod
     def get_converter():
-        if converter.current_converter == None:
+        if converter.current_converter is None:
             converter.current_converter = converter()
         return converter.current_converter
 
@@ -66,30 +66,30 @@ class converter:
             name = element.display_name
             if (element.supports_analize):
                 self.analizers[name] = element
-                if (self.default_analizer == None):
+                if (self.default_analizer is None):
                     self.default_analizer = element
             if (element.supports_play):
                 self.players[name] = element
-                if (self.default_player == None):
+                if (self.default_player is None):
                     self.default_player = element
             if (element.supports_convert):
                 self.converters[name] = element
-                if (self.default_converter == None):
+                if (self.default_converter is None):
                     self.default_converter = element
                 for types in element.disc_types:
                     if self.discs.count(types) == 0:
                         self.discs.append(types)
             if (element.supports_menu):
                 self.menuers[name] = element
-                if (self.default_menuer == None):
+                if (self.default_menuer is None):
                     self.default_menuer = element
             if (element.supports_mkiso):
                 self.mkiso[name] = element
-                if (self.default_mkiso == None):
+                if (self.default_mkiso is None):
                     self.default_mkiso = element
             if (element.supports_burn):
                 self.burners[name] = element
-                if (self.default_burner == None):
+                if (self.default_burner is None):
                     self.default_burner = element
 
 
@@ -151,27 +151,27 @@ class converter:
             The groups are, in this order: ANALIZERS, PLAYERS, CONVERTERS, MENUERS, BURNERS, MKISO
             (menuers are the programs that creates the mpeg files for menus) """
 
-        if (self.default_analizer != None):
+        if (self.default_analizer is not None):
             analizers = None
         else:
             analizers = []
-        if (self.default_player != None):
+        if (self.default_player is not None):
             players = None
         else:
             players = []
-        if (self.default_converter != None):
+        if (self.default_converter is not None):
             converters = None
         else:
             converters = []
-        if (self.default_menuer != None):
+        if (self.default_menuer is not None):
             menuers = None
         else:
             menuers = []
-        if (self.default_burner != None):
+        if (self.default_burner is not None):
             burners = None
         else:
             burners = []
-        if (self.default_mkiso != None):
+        if (self.default_mkiso is not None):
             mkiso = None
         else:
             mkiso = []
@@ -179,17 +179,17 @@ class converter:
         for element in self.c:
             e = element()
             name = e.display_name
-            if (e.supports_analize) and (analizers != None):
+            if (e.supports_analize) and (analizers is not None):
                 analizers.append(name)
-            if (e.supports_play) and (players != None):
+            if (e.supports_play) and (players is not None):
                 players.append(name)
-            if (e.supports_convert) and (converters != None):
+            if (e.supports_convert) and (converters is not None):
                 converters.append(name)
-            if (e.supports_menu) and (menuers != None):
+            if (e.supports_menu) and (menuers is not None):
                 menuers.append(name)
-            if (e.supports_burn) and (burners != None):
+            if (e.supports_burn) and (burners is not None):
                 burners.append(name)
-            if (e.supports_mkiso) and (mkiso != None):
+            if (e.supports_mkiso) and (mkiso is not None):
                 mkiso.append(name)
 
         return ( analizers, players, converters, menuers, burners, mkiso )
@@ -197,7 +197,7 @@ class converter:
     def get_film_player(self):
         """ returns a class for the desired film player, or the most priviledged if the desired is not installed """
 
-        if (self.config.film_player == None) or (self.config.film_player not in self.players):
+        if (self.config.film_player is None) or (self.config.film_player not in self.players):
             return self.default_player
         else:
             return self.players[self.config.film_player]
@@ -205,7 +205,7 @@ class converter:
     def get_film_analizer(self):
         """ returns a class for the desired film analizer, or the most priviledged if the desired is not installed """
 
-        if (self.config.film_analizer == None) or (self.config.film_analizer not in self.analizers):
+        if (self.config.film_analizer is None) or (self.config.film_analizer not in self.analizers):
             return self.default_analizer
         else:
             return self.analizers[self.config.film_analizer]
@@ -213,7 +213,7 @@ class converter:
     def get_menu_converter(self):
         """ returns a class for the desired menu converter, or the most priviledged if the desired is not installed """
 
-        if (self.config.menu_converter == None) or (self.config.menu_converter not in self.menuers):
+        if (self.config.menu_converter is None) or (self.config.menu_converter not in self.menuers):
             return self.default_menuer
         else:
             return self.menuers[self.config.menu_converter]
@@ -222,7 +222,7 @@ class converter:
         """ returns a class for the desired disc converter, or the most priviledged if the desired is not installed """
 
         # if there is a film converter chosen by the user, and it is installed in the system
-        if (self.config.film_converter != None) and (self.config.film_converter in self.converters):
+        if (self.config.film_converter is not None) and (self.config.film_converter in self.converters):
             # and that converter supports the current disc type
             if self.converters[self.config.film_converter].disc_types.count(self.config.disc_type) != 0:
                 # return that converter
@@ -241,7 +241,7 @@ class converter:
     def get_burner(self):
         """ returns a class for the desired burner, or the most priviledged if the desired is not installed """
 
-        if (self.config.burner == None) or (self.config.burner not in self.burners):
+        if (self.config.burner is None) or (self.config.burner not in self.burners):
             return self.default_burner
         else:
             return self.burners[self.config.burner]
@@ -249,7 +249,7 @@ class converter:
     def get_mkiso(self):
         """ returns a class for the desired mkiso, or the most priviledged if the desired is not installed """
 
-        if (self.config.mkiso == None) or (self.config.mkiso not in self.mkiso):
+        if (self.config.mkiso is None) or (self.config.mkiso not in self.mkiso):
             return self.default_mkiso
         else:
             return self.mkiso[self.config.mkiso]
diff --git a/src/devedeng/create_disk_window.py b/src/devedeng/create_disk_window.py
index 508c136..460e5ed 100644
--- a/src/devedeng/create_disk_window.py
+++ b/src/devedeng/create_disk_window.py
@@ -63,7 +63,7 @@ class create_disk_window:
         path = self.wpath.get_filename()
         name = self.wname.get_text()
         
-        if ((path == None) or (path == "") or (name == None) or (name == "")):
+        if ((path is None) or (path == "") or (name is None) or (name == "")):
             self.waccept.set_sensitive(False)
         else:
             self.waccept.set_sensitive(True)
diff --git a/src/devedeng/dvd_menu.py b/src/devedeng/dvd_menu.py
index d2ae2ae..3372808 100644
--- a/src/devedeng/dvd_menu.py
+++ b/src/devedeng/dvd_menu.py
@@ -254,7 +254,7 @@ class dvd_menu(devedeng.interface_manager.interface_manager):
     def write_text(self,text,text_type,xl,xr,y,alignment):
         """ Renders a line of text, in the rectangle delimited by xl,y-h;xr,y+h, with the specified alignment """
 
-        if text == None:
+        if text is None:
             return
 
         if text_type == "title":
@@ -298,7 +298,7 @@ class dvd_menu(devedeng.interface_manager.interface_manager):
         elif alignment == "center":
             x = ((xl + xr) / 2.0) - (extents[2] / 2.0)
 
-        if (bgcolor != None):
+        if (bgcolor is not None):
             self.cr.move_to(x+extents[0]+2,y-(extents[3]/2.0)-extents[1]+2)
             self.cr.set_source_rgba(bgcolor[0],bgcolor[1],bgcolor[2],bgcolor[3])
             self.cr.show_text(text)
@@ -339,7 +339,7 @@ class dvd_menu(devedeng.interface_manager.interface_manager):
 
         coordinates = []
 
-        if self.sf == None:
+        if self.sf is None:
             self.sf=cairo.ImageSurface(cairo.FORMAT_ARGB32,720,int(self.y))
             self.cr=cairo.Context(self.sf)
 
@@ -392,7 +392,7 @@ class dvd_menu(devedeng.interface_manager.interface_manager):
         if (page_number >= self.pages) and (page_number > 0):
             page_number -= 1
 
-        if self.wcurrent_page != None:
+        if self.wcurrent_page is not None:
             self.wcurrent_page.set_text(_("Page %(X)d of %(Y)d") % {"X":page_number+1 , "Y":self.pages})
         xl = left_margin_p
         xr = 720.0 - right_margin_p
@@ -502,7 +502,7 @@ class dvd_menu(devedeng.interface_manager.interface_manager):
         """ Callback to repaint the menu preview window when it
             sends the EXPOSE event """
 
-        if (self.sf == None):
+        if (self.sf is None):
             self.paint_menu(True, self.wshow_as_selected.get_active(), False, self.current_shown_page)
             if (self.current_shown_page >= self.pages):
                 self.current_shown_page = self.pages
diff --git a/src/devedeng/dvdauthor_converter.py b/src/devedeng/dvdauthor_converter.py
index 8fb06f5..a5a6e70 100644
--- a/src/devedeng/dvdauthor_converter.py
+++ b/src/devedeng/dvdauthor_converter.py
@@ -54,7 +54,7 @@ class dvdauthor_converter(devedeng.executor.executor):
 
 
     def process_stderr(self,data):
-        if (data != None) and (data[0] != ""):
+        if (data is not None) and (data[0] != ""):
             self.progress_bar[1].set_text(data[0])
         return
 
@@ -69,12 +69,12 @@ class dvdauthor_converter(devedeng.executor.executor):
         except:
             pass
 
-        if (len(file_movies) == 1) and (menu_entries == None):
+        if (len(file_movies) == 1) and (menu_entries is None):
             onlyone = True
         else:
             onlyone = False
 
-        if (menu_entries == None):
+        if (menu_entries is None):
             elements_per_menu = 1000
         else:
             elements_per_menu = len(menu_entries[0]["chapters"])
@@ -105,13 +105,13 @@ class dvdauthor_converter(devedeng.executor.executor):
             xml_file.write('\t\t<fpc>\n')
             xml_file.write('\t\t\tg0=100;\n')
             xml_file.write('\t\t\tg1=') #goto variable
-            if (menu_entries != None) and (start_with_menu):
+            if (menu_entries is not None) and (start_with_menu):
                 xml_file.write('0;\n') #show menu
             else:
                 xml_file.write('100;\n') #auto play
             xml_file.write('\t\t\tg2=1024;\n') #highlight?
             xml_file.write('\t\t\tg3=') #play all variable
-            if play_all_opt and (menu_entries != None) and (start_with_menu):
+            if play_all_opt and (menu_entries is not None) and (start_with_menu):
                 xml_file.write('1;\n') #auto play all
             else:
                 xml_file.write('0;\n') #do not play all
@@ -183,7 +183,7 @@ class dvdauthor_converter(devedeng.executor.executor):
                     title_list.append(counter)
                 counter += 1
 
-            if (menu_entries != None):
+            if (menu_entries is not None):
                 nmenues = len(menu_entries)
                 button_counter = 0
                 for menu_page in menu_entries:
@@ -223,14 +223,14 @@ class dvdauthor_converter(devedeng.executor.executor):
                             button_counter+=1
                         xml_file.write('\t\t\t\t</button>\n')
 
-                    if (menu_page["left"] != None):
+                    if (menu_page["left"] is not None):
                         xml_file.write('\t\t\t\t<button name="'+menu_page["left"]+'"> g1=')
                         xml_file.write(str(menu_number-1))
                         xml_file.write('; g2=1024; jump menu ')
                         xml_file.write(str(menu_number))
                         xml_file.write('; </button>\n')
 
-                    if (menu_page["right"] != None):
+                    if (menu_page["right"] is not None):
                         xml_file.write('\t\t\t\t<button name="'+menu_page["right"]+'"> g1=')
                         xml_file.write(str(menu_number+1))
                         xml_file.write('; g2=1024; jump menu ')
diff --git a/src/devedeng/executor.py b/src/devedeng/executor.py
index 278ed4f..c6b8db3 100644
--- a/src/devedeng/executor.py
+++ b/src/devedeng/executor.py
@@ -62,7 +62,7 @@ class executor(GObject.GObject):
 
     def add_dependency2(self, dep):
 
-        if (self.dependencies == None):
+        if (self.dependencies is None):
             self.dependencies = []
 
         if (self.dependencies.count(dep) == 0):
@@ -76,7 +76,7 @@ class executor(GObject.GObject):
     def remove_dependency(self,process):
         # dependencies are removed only in the parent because the running class have all the processes, parents and childs, and calls
         # this method on all of them
-        if (self.dependencies != None):
+        if (self.dependencies is not None):
             tmp2 = []
             for dep in self.dependencies:
                 if dep != process:
@@ -90,7 +90,7 @@ class executor(GObject.GObject):
     def add_child_process(self,child):
 
         # the childs have the same dependencies than the parent process because, from outside, it is viewed as a single process
-        if self.dependencies != None:
+        if self.dependencies is not None:
             for dep in self.dependencies:
                 child.add_dependency(dep)
 
@@ -143,18 +143,18 @@ class executor(GObject.GObject):
 
     def launch_process(self,command,redirect_output = True):
 
-        if command != None:
+        if command is not None:
             self.launch_command = "\n\nLaunching:"
             for e in command:
                 self.launch_command += (" "+e)
             self.launch_command += "\n"
 
         self.config.append_log(self.text)
-        if command != None:
+        if command is not None:
             self.config.append_log(self.launch_command)
 
         try:
-            if (self.stdin_file != None):
+            if (self.stdin_file is not None):
                 self.handle = subprocess.Popen(command,stdin = subprocess.PIPE, stdout = subprocess.PIPE, stderr = subprocess.PIPE)
                 self.channel_stdin = GLib.IOChannel(self.handle.stdin.fileno())
                 self.channel_stdin.add_watch(GLib.IO_OUT | GLib.IO_HUP, self.read_stdin_from_file)
@@ -172,7 +172,7 @@ class executor(GObject.GObject):
             self.stderr_buf = ""
             self.channel_stdout = GLib.IOChannel(self.handle.stdout.fileno())
             self.channel_stderr = GLib.IOChannel(self.handle.stderr.fileno())
-            if (self.stdout_file != None):
+            if (self.stdout_file is not None):
                 self.channel_stdout.add_watch(GLib.IO_IN | GLib.IO_HUP,self.read_stdout_to_file)
                 self.file_out = open(self.stdout_file,"wb")
             else:
@@ -208,10 +208,10 @@ class executor(GObject.GObject):
 
     def run_pulse(self,v = None):
 
-        if self.progress_bar == None:
+        if self.progress_bar is None:
             return
 
-        if self.pulse_text != None:
+        if self.pulse_text is not None:
             self.progress_bar[1].set_text(self.pulse_text)
         self.progress_bar[1].pulse()
         return True
@@ -221,7 +221,7 @@ class executor(GObject.GObject):
 
         if (condition != GLib.IO_IN):
             self.channel_stdout = None
-            if ((self.channel_stderr == None) and (self.channel_stdin == None)):
+            if ((self.channel_stderr is None) and (self.channel_stdin is None)):
                 self.wait_end()
             return False
         else:
@@ -236,7 +236,7 @@ class executor(GObject.GObject):
         if (len(line_data) == 0):
             self.channel_stdin = None
             self.handle.stdin.close()
-            if ((self.channel_stderr == None) and (self.channel_stdout == None)):
+            if ((self.channel_stderr is None) and (self.channel_stdout is None)):
                 self.wait_end()
             return False
         else:
@@ -248,7 +248,7 @@ class executor(GObject.GObject):
 
         if (condition != GLib.IO_IN):
             self.channel_stdout = None
-            if ((self.channel_stderr == None) and (self.channel_stdin == None)):
+            if ((self.channel_stderr is None) and (self.channel_stdin is None)):
                 self.wait_end()
             return False
         else:
@@ -274,7 +274,7 @@ class executor(GObject.GObject):
 
         if (condition != GLib.IO_IN):
             self.channel_stderr = None
-            if (((self.channel_stdout == None) or (self.stdout_file != None)) and ((self.channel_stdin == None) or (self.stdin_file != None))):
+            if (((self.channel_stdout is None) or (self.stdout_file is not None)) and ((self.channel_stdin is None) or (self.stdin_file is not None))):
                 self.wait_end()
             return False
         else:
@@ -300,15 +300,16 @@ class executor(GObject.GObject):
 
         """ Called to kill this process. """
 
-        if self.handle==None:
+        if self.handle is None:
             return
+
         self.killed = True
         os.kill(self.handle.pid,signal.SIGKILL)
 
 
     def wait_end(self):
 
-        if self.handle != None:
+        if self.handle is not None:
             retval = self.handle.wait()
             self.handle = None
         else:
diff --git a/src/devedeng/ffprobe.py b/src/devedeng/ffprobe.py
index 3fc11af..839f0a5 100644
--- a/src/devedeng/ffprobe.py
+++ b/src/devedeng/ffprobe.py
@@ -125,11 +125,11 @@ class ffprobe(devedeng.executor.executor):
                     self.original_audiorate_uncompressed = int(float(element["sample_rate"]))
 
         self.original_size = str(self.original_width)+"x"+str(self.original_height)
-        if (self.original_aspect_ratio == None) or (self.original_aspect_ratio <= 1.0):
+        if (self.original_aspect_ratio is None) or (self.original_aspect_ratio <= 1.0):
             if (self.original_height != 0):
                 self.original_aspect_ratio = (float(self.original_width))/(float(self.original_height))
 
-        if (self.original_aspect_ratio != None):
+        if (self.original_aspect_ratio is not None):
             self.original_aspect_ratio = (float(int(self.original_aspect_ratio*1000.0)))/1000.0
 
         if (len(self.video_list) == 0):
diff --git a/src/devedeng/file_copy.py b/src/devedeng/file_copy.py
index 421c126..d0bdf41 100644
--- a/src/devedeng/file_copy.py
+++ b/src/devedeng/file_copy.py
@@ -38,7 +38,7 @@ class file_copy(devedeng.executor.executor):
 
     def process_stdout(self,data):
 
-        if (data == None) or (len(data) == 0):
+        if (data is None) or (len(data) == 0):
             return
         if (data[0].startswith("Copied ")):
             pos = data[0].find("%")
@@ -51,4 +51,4 @@ class file_copy(devedeng.executor.executor):
 
     def process_stderr(self,data):
 
-        return
\ No newline at end of file
+        return
diff --git a/src/devedeng/file_movie.py b/src/devedeng/file_movie.py
index cc39bb8..a0f2724 100644
--- a/src/devedeng/file_movie.py
+++ b/src/devedeng/file_movie.py
@@ -43,7 +43,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
         self.set_type(None, self.config.disc_type)
         self.config.connect('disc_type',self.set_type)
 
-        if list_files == None:
+        if list_files is None:
             self.add_text("file_name", file_name)
             self.add_text("title_name", os.path.splitext(os.path.basename(file_name))[0])
             self.add_label("original_size",None)
@@ -100,7 +100,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
         self.add_colorbutton("subt_outline_color", self.config.subt_outline_color)
         self.add_float_adjustment("subt_thickness", self.config.subt_outline_thickness)
 
-        if list_files == None:
+        if list_files is None:
             self.add_list("subtitles_list")
         else:
             self.add_list("files_to_set")
@@ -138,7 +138,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
         self.add_enable_disable("is_mpeg_ps", [], is_mpeg_ps_list)
         self.add_enable_disable("no_reencode_audio_video", [], no_reencode_audio_video_list)
 
-        if list_files == None:
+        if list_files is None:
             cv = devedeng.converter.converter.get_converter()
             film_analizer = (cv.get_film_analizer())()
             if (film_analizer.get_film_data(self.file_name)):
@@ -400,7 +400,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
 
     def set_type(self,obj = None,disc_type = None):
 
-        if (disc_type != None):
+        if (disc_type is not None):
             self.disc_type = disc_type
 
 
@@ -415,7 +415,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
 
     def properties(self):
 
-        if (self.wfile_properties != None):
+        if (self.wfile_properties is not None):
             self.wfile_properties.present()
             return
 
@@ -528,7 +528,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
             self.wframe_division_chapters.hide()
             self.wnotebook.remove_page(5)
 
-        if self.list_files == None:
+        if self.list_files is None:
             self.wframe_title.show()
             self.wframe_fileinfo.show()
             self.wframe_multiproperties.hide()
@@ -580,7 +580,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
         self.config.subt_fill_color = self.subt_fill_color
         self.config.subt_outline_color = self.subt_outline_color
         self.config.subt_outline_thickness = self.subt_thickness
-        if self.list_files == None:
+        if self.list_files is None:
             # editing file properties
             self.set_final_rates()
             self.set_final_size_aspect()
@@ -601,7 +601,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
 
     def on_button_cancel_clicked(self,b):
 
-        if self.list_files == None:
+        if self.list_files is None:
             self.restore_ui()
 
         self.wfile_properties.destroy()
@@ -621,7 +621,7 @@ class file_movie(devedeng.interface_manager.interface_manager):
         selection = self.wtreview_subtitles.get_selection()
         model, treeiter = selection.get_selected()
 
-        if treeiter != None:
+        if treeiter is not None:
             return ( (model, treeiter) )
         else:
             return ( (None, None) )
@@ -630,14 +630,14 @@ class file_movie(devedeng.interface_manager.interface_manager):
     def on_del_subtitles_clicked(self,b):
 
         model, treeiter = self.get_selected_subtitle()
-        if (model != None):
+        if (model is not None):
             model.remove(treeiter)
 
 
     def on_treeview_subtitles_cursor_changed(self,b):
 
         model, treeiter = self.get_selected_subtitle()
-        if (model == None):
+        if (model is None):
             self.wdel_subtitles.set_sensitive(False)
         else:
             self.wdel_subtitles.set_sensitive(True)
diff --git a/src/devedeng/interface_manager.py b/src/devedeng/interface_manager.py
index b5c6f6f..08d1f64 100644
--- a/src/devedeng/interface_manager.py
+++ b/src/devedeng/interface_manager.py
@@ -46,7 +46,7 @@ class interface_manager(GObject.GObject):
             value for the variable will be the name of the active
             radiobutton """
 
-        if (default_value != None):
+        if (default_value is not None):
             exec('self.'+group_name+' = "'+str(default_value)+'"')
         else:
             exec('self.'+group_name+' = None')
@@ -74,7 +74,7 @@ class interface_manager(GObject.GObject):
             element with the same name (must be a Gtk.TextEntry or a Gtk.Label).
             The default value can be a text or None """
 
-        if (default_value != None):
+        if (default_value is not None):
             exec('self.'+text_name+' = "'+str(default_value).replace('\"','\\"')+'"')
         else:
             exec('self.'+text_name+' = None')
@@ -169,7 +169,7 @@ class interface_manager(GObject.GObject):
             obj = eval('self.'+key)
             builder.get_object(obj).set_active(True)
             callback = self.interface_groups[key][1]
-            if (callback != None):
+            if (callback is not None):
                 for element in self.interface_groups[key][0]:
                     obj = builder.get_object(element)
                     obj.connect("toggled",callback)
@@ -179,7 +179,7 @@ class interface_manager(GObject.GObject):
             obj = builder.get_object(element[0])
             obj.set_active(value)
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("toggled",callback)
 
         for element in self.interface_dualtoggles:
@@ -191,45 +191,45 @@ class interface_manager(GObject.GObject):
             else:
                 obj2.set_active(True)
             callback = element[2]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("toggled",callback)
 
         for element in self.interface_text:
             value = eval('self.'+element[0])
             obj = builder.get_object(element[0])
-            if (value != None):
+            if (value is not None):
                 obj.set_text(value)
             else:
                 obj.set_text("")
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("changed",callback)
 
         for element in self.interface_labels:
             value = eval('self.'+element)
             obj = builder.get_object(element)
-            if obj != None:
-                if (value != None):
+            if obj is not None:
+                if (value is not None):
                     obj.set_text(str(value))
                 else:
                     obj.set_text("")
 
         for element in self.interface_integer_adjustments:
             obj = builder.get_object(element[0])
-            if obj != None:
+            if obj is not None:
                 value = eval('self.'+element[0])
                 obj.set_value(float(value))
                 callback = element[1]
-                if (callback != None):
+                if (callback is not None):
                     obj.connect("value_changed",callback)
 
         for element in self.interface_float_adjustments:
             obj = builder.get_object(element[0])
-            if obj != None:
+            if obj is not None:
                 value = eval('self.'+element[0])
                 obj.set_value(value)
                 callback = element[1]
-                if (callback != None):
+                if (callback is not None):
                     obj.connect("value_changed",callback)
 
         for element in self.interface_lists:
@@ -239,7 +239,7 @@ class interface_manager(GObject.GObject):
             for item in obj:
                 the_liststore.append(item)
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 the_liststore.connect("row_changed",callback)
                 the_liststore.connect("row_deleted",callback)
                 the_liststore.connect("row_inserted",callback)
@@ -252,25 +252,25 @@ class interface_manager(GObject.GObject):
             obj.set_color(objcolor)
             obj.set_alpha(int(value[3]*65535.0))
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("color_set",callback)
 
         for element in self.interface_fontbuttons:
             value = eval('self.'+element[0])
             obj = builder.get_object(element[0])
-            if (value != None):
+            if (value is not None):
                 obj.set_font(value)
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("font_set",callback)
 
         for element in self.interface_filebuttons:
             value = eval('self.'+element[0])
             obj = builder.get_object(element[0])
-            if (value != None):
+            if (value is not None):
                 obj.set_filename(value)
             callback = element[1]
-            if (callback != None):
+            if (callback is not None):
                 obj.connect("file_set",callback)
 
         for element in self.interface_comboboxes:
@@ -287,7 +287,7 @@ class interface_manager(GObject.GObject):
                 counter += 1
             the_combo.set_active(dv)
             callback = element[2]
-            if (callback != None):
+            if (callback is not None):
                 the_combo.connect("changed",callback)
 
         self.interface_show_hide_obj = {}
@@ -415,12 +415,12 @@ class interface_manager(GObject.GObject):
 
         for element in self.interface_integer_adjustments:
             obj = builder.get_object(element[0])
-            if obj != None:
+            if obj is not None:
                 exec('self.'+element[0]+' = int(obj.get_value())')
 
         for element in self.interface_float_adjustments:
             obj = builder.get_object(element[0])
-            if obj != None:
+            if obj is not None:
                 exec('self.'+element[0]+' = obj.get_value()')
 
         for element in self.interface_colorbuttons:
diff --git a/src/devedeng/message.py b/src/devedeng/message.py
index 4949084..9b873eb 100644
--- a/src/devedeng/message.py
+++ b/src/devedeng/message.py
@@ -38,7 +38,7 @@ class message_window:
         wmessage_liststore = builder.get_object("liststore_elements")
         wmessage_window.show_all()
 
-        if (list_data == None):
+        if (list_data is None):
             wmessage_list.hide()
         else:
             for element in list_data:
diff --git a/src/devedeng/opensave.py b/src/devedeng/opensave.py
index d0bd588..8b3352d 100644
--- a/src/devedeng/opensave.py
+++ b/src/devedeng/opensave.py
@@ -38,7 +38,7 @@ class opensave_window:
             builder.add_from_file(os.path.join(self.config.glade,"wopen_project.ui"))
         builder.connect_signals(self)
         w_window = builder.get_object("data_project")
-        if current_file != None:
+        if current_file is not None:
             w_window.set_filename(current_file)
 
         file_filter_projects=Gtk.FileFilter()
@@ -59,4 +59,4 @@ class opensave_window:
         if (retval == 1):
             return self.final_filename
         else:
-            return None
\ No newline at end of file
+            return None
diff --git a/src/devedeng/project.py b/src/devedeng/project.py
index de153e7..e742be4 100644
--- a/src/devedeng/project.py
+++ b/src/devedeng/project.py
@@ -95,7 +95,7 @@ class devede_project:
         self.wcreate_menu.set_active(True)
 
         self.config.connect('disc_type',self.set_type)
-        if (self.disc_type != None):
+        if (self.disc_type is not None):
             self.set_type(None, self.disc_type)
 
         self.wmain_window.drag_dest_set(Gtk.DestDefaults.ALL,[],Gdk.DragAction.COPY)
@@ -109,7 +109,7 @@ class devede_project:
             in the main window to it. Also leaves everything ready to start creating a
             new disc """
 
-        if (disc_type != None):
+        if (disc_type is not None):
             self.disc_type = disc_type
         self.wmain_window.show_all()
         self.set_interface_status(None)
@@ -135,7 +135,7 @@ class devede_project:
         selection = self.wfiles.get_selection()
         model, treeiter = selection.get_selected()
 
-        if treeiter != None:
+        if treeiter is not None:
             element = model[treeiter][0]
             position = 0
             for row in self.wfiles.get_model():
@@ -172,7 +172,7 @@ class devede_project:
         self.pal = self.wuse_pal.get_active()
 
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None):
+        if (element is None):
             self.wdelete_file.set_sensitive(False)
             self.wup_file.set_sensitive(False)
             self.wdown_file.set_sensitive(False)
@@ -264,7 +264,7 @@ class devede_project:
     def on_delete_file_clicked(self,b):
 
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None):
+        if (element is None):
             return
 
         ask_w = devedeng.ask.ask_window()
@@ -278,7 +278,7 @@ class devede_project:
     def on_up_file_clicked(self,b):
 
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None) or (position == 0):
+        if (element is None) or (position == 0):
             return
 
         last_element = self.wfiles.get_model()[position-1]
@@ -289,7 +289,7 @@ class devede_project:
     def on_down_file_clicked(self,b):
 
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None) or (position == (len(self.wfiles.get_model())-1)):
+        if (element is None) or (position == (len(self.wfiles.get_model())-1)):
             return
 
         last_element = self.wfiles.get_model()[position+1]
@@ -299,7 +299,7 @@ class devede_project:
 
     def on_properties_file_clicked(self,b):
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None):
+        if (element is None):
             return
         element.properties()
 
@@ -572,7 +572,7 @@ class devede_project:
 
         if value == 0:
             ended = devedeng.end_job.end_window()
-            if self.disc_image_name == None:
+            if self.disc_image_name is None:
                 do_burn = False
             else:
                 do_burn = True
@@ -597,7 +597,7 @@ class devede_project:
     def on_preview_file_clicked(self,b):
 
         (element, position, model, treeiter) = self.get_current_file()
-        if (element == None):
+        if (element is None):
             return
         element.do_preview()
 
@@ -639,7 +639,7 @@ class devede_project:
 
 
     def on_save_activate(self,b):
-        if self.project_file != None:
+        if self.project_file is not None:
             self.save_current_project()
         else:
             self.on_save_as_activate(None)
@@ -650,7 +650,7 @@ class devede_project:
         while True:
             w = devedeng.opensave.opensave_window(True)
             retval = w.run(self.project_file)
-            if retval == None:
+            if retval is None:
                 return
             if not retval.endswith(".devedeng"):
                 retval += ".devedeng"
@@ -666,7 +666,7 @@ class devede_project:
     def on_load_activate(self,b):
         w = devedeng.opensave.opensave_window(False)
         retval = w.run()
-        if retval != None:
+        if retval is not None:
             self.load_project(retval)
 
 
diff --git a/src/devedeng/runner.py b/src/devedeng/runner.py
index 15d5854..3f82e3e 100644
--- a/src/devedeng/runner.py
+++ b/src/devedeng/runner.py
@@ -107,7 +107,7 @@ class runner(GObject.GObject):
             # * the process object
             # * the list of dependencies, or None if there are no more dependencies
             # * the progress bar being used by this process
-            if (element.dependencies == None) and (element.progress_bar == None):
+            if (element.dependencies is None) and (element.progress_bar is None):
                 element.connect("ended",self.process_ended)
                 element.run(self.progress_bars[0])
                 element.progress_bar = self.progress_bars[0]
@@ -158,4 +158,4 @@ class runner(GObject.GObject):
             self.run(False)
         else:
             self.wprogress.destroy()
-            self.emit("done",0) # no error
\ No newline at end of file
+            self.emit("done",0) # no error
diff --git a/src/devedeng/subtitles_mux.py b/src/devedeng/subtitles_mux.py
index a46795d..a28bfc7 100644
--- a/src/devedeng/subtitles_mux.py
+++ b/src/devedeng/subtitles_mux.py
@@ -98,7 +98,7 @@ class subtitles_mux(devedeng.executor.executor):
 
     def process_stderr(self,data):
 
-        if (data == None) or (len(data) == 0):
+        if (data is None) or (len(data) == 0):
             return
 
         if self.duration == 0:
@@ -114,4 +114,4 @@ class subtitles_mux(devedeng.executor.executor):
             self.progress_bar[1].set_fraction(t)
             self.progress_bar[1].set_text("%.1f%%" % (100.0 * t))
 
-        return
\ No newline at end of file
+        return
diff --git a/src/devedeng/title.py b/src/devedeng/title.py
index bbe90f8..604741d 100644
--- a/src/devedeng/title.py
+++ b/src/devedeng/title.py
@@ -27,7 +27,7 @@ class title(GObject.GObject):
         GObject.GObject.__init__(self)
         self.config = config
         self.file_treeview = file_treeview
-        if (title_name == None):
+        if (title_name is None):
             title.counter += 1
             self.title_name = _("Title %(X)d") % {"X":title.counter}
         else: