diff --git a/atrcopy/__init__.py b/atrcopy/__init__.py
index 0c1c99f..43e7823 100644
--- a/atrcopy/__init__.py
+++ b/atrcopy/__init__.py
@@ -188,17 +188,17 @@ def assemble(image, source_files, data_files, obj_files, run_addr=""):
             asm = pyatasm.Assemble(name)
         except SyntaxError, e:
             raise AtrError("Assembly error: %s" % e.msg)
-        log.debug("Assembled %s into:" % name)
+        if _dbg: log.debug("Assembled %s into:" % name)
         for first, last, object_code in asm.segments:
             s = segments.add_segment(object_code, first)
-            log.debug("  %s" % s.name)
+            if _dbg: log.debug("  %s" % s.name)
             print "adding %s from %s assembly" % (s, name)
     for name in data_files:
         if "@" not in name:
             raise AtrError("Data files must include a load address specified with the @ char")
         name, addr = name.rsplit("@", 1)
         first = text_to_int(addr)
-        log.debug("Adding data file %s at $%04x" % (name, first))
+        if _dbg: log.debug("Adding data file %s at $%04x" % (name, first))
         subset = slice(0, sys.maxint)
         if "[" in name and "]" in name:
             name, slicetext = name.rsplit("[", 1)
@@ -218,7 +218,7 @@ def assemble(image, source_files, data_files, obj_files, run_addr=""):
         with open(name, 'rb') as fh:
             data = fh.read()[subset]
             s = segments.add_segment(data, first)
-            log.debug("read data for %s" % s.name)
+            if _dbg: log.debug("read data for %s" % s.name)
     for name in obj_files:
         parser = find_diskimage(name)
         if parser and parser.image:
diff --git a/atrcopy/ataridos.py b/atrcopy/ataridos.py
index b17f5a9..4290aff 100644
--- a/atrcopy/ataridos.py
+++ b/atrcopy/ataridos.py
@@ -22,7 +22,7 @@ class AtariDosWriteableSector(WriteableSector):
         self.data[index + 0] = (self.file_num << 2) | (hi & 0x03)
         self.data[index + 1] = lo
         self.data[index + 2] = self.used
-        log.debug("sector metadata for %d: %s" % (self._sector_num, self.data[index:index + 3]))
+        if _dbg: log.debug("sector metadata for %d: %s" % (self._sector_num, self.data[index:index + 3]))
         # file number will be added later when known.
 
 
@@ -31,10 +31,10 @@ class AtariDosVTOC(VTOC):
         self.vtoc1 = segments[0].data
         bits = np.unpackbits(self.vtoc1[0x0a:0x64])
         self.sector_map[0:720] = bits
-        log.debug("vtoc before:\n%s" % str(self))
+        if _dbg: log.debug("vtoc before:\n%s" % str(self))
 
     def calc_bitmap(self):
-        log.debug("vtoc after:\n%s" % str(self))
+        if _dbg: log.debug("vtoc after:\n%s" % str(self))
         packed = np.packbits(self.sector_map[0:720])
         self.vtoc1[0x0a:0x64] = packed
         s = WriteableSector(self.sector_size, self.vtoc1)
@@ -52,7 +52,7 @@ class AtariDosDirectory(Directory):
 
     def encode_dirent(self, dirent):
         data = dirent.encode_dirent()
-        log.debug("encoded dirent: %s" % data)
+        if _dbg: log.debug("encoded dirent: %s" % data)
         return data
 
     def set_sector_numbers(self, image):
@@ -225,7 +225,7 @@ class AtariDosDirent(Dirent):
         self.file_num = index
         self.dos_2 = True
         self.in_use = True
-        log.debug("set_values: %s" % self)
+        if _dbg: log.debug("set_values: %s" % self)
 
 
 class MydosDirent(AtariDosDirent):
@@ -279,7 +279,7 @@ class AtariDosFile(object):
         pos = 0
         style_pos = 0
         first = True
-        log.debug("Initial parsing: size=%d" % self.size)
+        if _dbg: log.debug("Initial parsing: size=%d" % self.size)
         while pos < self.size:
             if pos + 1 < self.size:
                 header, = b[pos:pos+2].view(dtype='<u2')
@@ -294,7 +294,7 @@ class AtariDosFile(object):
                 continue
             elif first:
                 raise InvalidBinaryFile("Object file doesn't start with 0xffff")
-            log.debug("header parsing: header=0x%x" % header)
+            if _dbg: log.debug("header parsing: header=0x%x" % header)
             if len(b[pos:pos + 4]) < 4:
                 self.segments.append(ObjSegment(r[pos:pos + 4], 0, 0, 0, len(b[pos:pos + 4]), "Short Segment Header"))
                 break
@@ -534,7 +534,7 @@ class AtariDosDiskImage(DiskImageBase):
                 files.append(dirent)
                 if not dirent.is_sane:
                     self.all_sane = False
-                    log.debug("dirent %d not sane: %s" % (num, dirent))
+                    if _dbg: log.debug("dirent %d not sane: %s" % (num, dirent))
             elif dirent.flag == 0:
                 break
             if directory is not None:
@@ -646,7 +646,7 @@ class AtariDosDiskImage(DiskImageBase):
                 binary = AtariDosFile(segment.rawdata)
                 segments_out.extend(binary.segments)
             except InvalidBinaryFile:
-                log.debug("%s not a binary file; skipping segment generation" % str(segment))
+                if _dbg: log.debug("%s not a binary file; skipping segment generation" % str(segment))
         return segments_out
 
     def create_executable_file_image(self, segments, run_addr=None):
diff --git a/atrcopy/cartridge.py b/atrcopy/cartridge.py
index 61e5e41..2638921 100644
--- a/atrcopy/cartridge.py
+++ b/atrcopy/cartridge.py
@@ -227,7 +227,7 @@ class AtariCartImage(DiskImageBase):
             return
         k, rem = divmod((len(self) - len(self.header)), 1024)
         c = get_cart(self.cart_type)
-        log.debug("checking type=%d, k=%d, rem=%d for %s, %s" % (self.cart_type, k, rem, c[1], c[2]))
+        if _dbg: log.debug("checking type=%d, k=%d, rem=%d for %s, %s" % (self.cart_type, k, rem, c[1], c[2]))
         if rem > 0:
             raise InvalidDiskImage("Cart not multiple of 1K")
         if k != c[2]:
diff --git a/atrcopy/diskimages.py b/atrcopy/diskimages.py
index 2b0d4ac..65c7ef2 100644
--- a/atrcopy/diskimages.py
+++ b/atrcopy/diskimages.py
@@ -348,7 +348,7 @@ class DiskImageBase(object):
     def write_sector_list(self, sector_list):
         for sector in sector_list:
             pos, size = self.header.get_pos(sector.sector_num)
-            log.debug("writing: %s at %d" % (sector, pos))
+            if _dbg: log.debug("writing: %s at %d" % (sector, pos))
             self.bytes[pos:pos + size] = sector.data
 
     def delete_file(self, filename):
@@ -373,7 +373,7 @@ class DiskImageBase(object):
         try:
             vtoc = self.get_vtoc_object()
             for sector_num, pos, size in vtoc.iter_free_sectors():
-                log.debug("shredding: sector %s at %d, fill value=%d" % (sector_num, pos, fill_value))
+                if _dbg: log.debug("shredding: sector %s at %d, fill value=%d" % (sector_num, pos, fill_value))
                 self.bytes[pos:pos + size] = fill_value
         except AtrError:
             self.rollback_transaction(state)
diff --git a/atrcopy/dos33.py b/atrcopy/dos33.py
index f2c228e..16c7724 100644
--- a/atrcopy/dos33.py
+++ b/atrcopy/dos33.py
@@ -24,7 +24,7 @@ class Dos33TSSector(WriteableSector):
             t, s = self.header.track_from_sector(sector.sector_num)
             self.data[index] = t
             self.data[index + 1] = s
-            log.debug("tslist entry #%d: %d, %d" % (index, t, s))
+            if _dbg: log.debug("tslist entry #%d: %d, %d" % (index, t, s))
             index += 2
 
     def get_tslist(self):
@@ -93,10 +93,10 @@ class Dos33VTOC(VTOC):
         # so we need to reorder them using numpy's indexing before stuffing
         # them into the sector map
         self.sector_map[0:self.max_sectors] = bits[self.vtoc_bit_reorder_index]
-        log.debug("vtoc before:\n%s" % str(self))
+        if _dbg: log.debug("vtoc before:\n%s" % str(self))
 
     def calc_bitmap(self):
-        log.debug("vtoc after:\n%s" % str(self))
+        if _dbg: log.debug("vtoc after:\n%s" % str(self))
 
         # reverse the process from above, so swap the order of every 16 bits,
         # turn them into bytes, then stuff them back into the vtoc. The bit
@@ -129,7 +129,7 @@ class Dos33Directory(Directory):
 
     def encode_dirent(self, dirent):
         data = dirent.encode_dirent()
-        log.debug("encoded dirent: %s" % data)
+        if _dbg: log.debug("encoded dirent: %s" % data)
         return data
 
     def set_sector_numbers(self, image):
@@ -140,7 +140,7 @@ class Dos33Directory(Directory):
             t, s = image.header.track_from_sector(next_sector)
             sector.data[1] = t
             sector.data[2] = s
-            log.debug("directory sector %d -> next = %d" % (sector.sector_num, next_sector))
+            if _dbg: log.debug("directory sector %d -> next = %d" % (sector.sector_num, next_sector))
             current_sector = next_sector
 
 
@@ -266,7 +266,7 @@ class Dos33Dirent(Dirent):
         tslist = BaseSectorList(header)
         for start in range(0, len(sector_list), header.ts_pairs):
             end = min(start + header.ts_pairs, len(sector_list))
-            log.debug("ts: %d-%d" % (start, end))
+            if _dbg: log.debug("ts: %d-%d" % (start, end))
             s = Dos33TSSector(header, sector_list, start, end)
             s.ts_start, s.ts_end = start, end
             tslist.append(s)
@@ -274,7 +274,7 @@ class Dos33Dirent(Dirent):
         vtoc.assign_sector_numbers(self, tslist)
         sector_list.extend(tslist)
         self.track, self.sector = header.track_from_sector(tslist[0].sector_num)
-        log.debug("track/sector lists:\n%s" % str(tslist))
+        if _dbg: log.debug("track/sector lists:\n%s" % str(tslist))
 
     def sanity_check(self, image):
         if self.deleted:
@@ -294,7 +294,7 @@ class Dos33Dirent(Dirent):
         sector_map = []
         while sector_num > 0:
             image.assert_valid_sector(sector_num)
-            log.debug("reading track/sector list at %d for %s" % (sector_num, self))
+            if _dbg: log.debug("reading track/sector list at %d for %s" % (sector_num, self))
             data, _ = image.get_sectors(sector_num)
             sector = Dos33TSSector(image.header, data=data)
             sector.sector_num = sector_num
@@ -318,7 +318,7 @@ class Dos33Dirent(Dirent):
         if not self.is_sane:
             raise InvalidDirent("Invalid directory entry '%s'" % str(self))
         self.get_track_sector_list(image)
-        log.debug("start_read: %s, t/s list: %s" % (str(self), str(self.sector_map)))
+        if _dbg: log.debug("start_read: %s, t/s list: %s" % (str(self), str(self.sector_map)))
         self.current_sector_index = 0
         self.current_read = self.num_sectors
 
@@ -327,7 +327,7 @@ class Dos33Dirent(Dirent):
             sector = self.sector_map[self.current_sector_index]
         except IndexError:
             sector = -1  # force ByteNotInFile166 error at next read
-        log.debug("read_sector: index %d=%d in %s" % (self.current_sector_index,sector, str(self)))
+        if _dbg: log.debug("read_sector: index %d=%d in %s" % (self.current_sector_index,sector, str(self)))
         last = (self.current_sector_index == len(self.sector_map) - 1)
         raw, pos, size = image.get_raw_bytes(sector)
         bytes, num_data_bytes = self.process_raw_sector(image, raw)
@@ -415,7 +415,7 @@ class Dos33DiskImage(DiskImageBase):
             else:
                 raise InvalidDiskImage("Invalid VTOC location for DOS 3.3")
 
-        log.debug("DOS 3.3 byte swap: %s" % swap_order)
+        if _dbg: log.debug("DOS 3.3 byte swap: %s" % swap_order)
 
     vtoc_type = np.dtype([
         ('unused1', 'S1'),
@@ -453,7 +453,7 @@ class Dos33DiskImage(DiskImageBase):
         files = []
         while sector > 0:
             self.assert_valid_sector(sector)
-            log.debug("reading catalog sector: %d" % sector)
+            if _dbg: log.debug("reading catalog sector: %d" % sector)
             values, style = self.get_sectors(sector)
             sector = self.header.sector_from_track(values[1], values[2])
             i = 0xb
@@ -468,7 +468,7 @@ class Dos33DiskImage(DiskImageBase):
                     files.append(dirent)
                 if directory is not None:
                     directory.set(num, dirent)
-                log.debug("valid directory entry %s" % dirent)
+                if _dbg: log.debug("valid directory entry %s" % dirent)
                 i += 0x23
                 num += 1
         self.files = files
@@ -525,7 +525,7 @@ class Dos33DiskImage(DiskImageBase):
         sector = self.header.first_directory
         while sector > 0:
             self.assert_valid_sector(sector)
-            log.debug("loading directory segment from catalog sector %d" % sector)
+            if _dbg: log.debug("loading directory segment from catalog sector %d" % sector)
             raw, pos, size = self.get_raw_bytes(sector)
             byte_order.extend(range(pos, pos + size))
             sector = self.header.sector_from_track(raw[1], raw[2])
@@ -557,7 +557,7 @@ class Dos33DiskImage(DiskImageBase):
         self.assert_valid_sector(sector_num)
         raw, _, _ = self.get_raw_bytes(sector_num)
         next_sector = self.header.sector_from_track(raw[1], raw[2])
-        log.debug("checking catalog sector %d, next catalog sector: %d" % (sector_num, next_sector))
+        if _dbg: log.debug("checking catalog sector %d, next catalog sector: %d" % (sector_num, next_sector))
         if next_sector == 0:
             raise NoSpaceInDirectory("No space left in catalog")
         return sector_num, next_sector
@@ -596,7 +596,7 @@ class Dos33DiskImage(DiskImageBase):
         for s in segments:
             origin = min(origin, s.start_addr)
             last = max(last, s.start_addr + len(s))
-            log.debug("contiguous bytes needed: %04x - %04x" % (origin, last))
+            if _dbg: log.debug("contiguous bytes needed: %04x - %04x" % (origin, last))
         if run_addr and run_addr != origin:
             # check if run_addr points to some location that has data
             found = False
@@ -652,7 +652,7 @@ class Dos33BinFile(object):
         pos = 0
         style_pos = 0
         first = True
-        log.debug("Initial parsing: size=%d" % self.size)
+        if _dbg: log.debug("Initial parsing: size=%d" % self.size)
         if len(b[pos:pos + 4]) == 4:
             start, count = b[pos:pos + 4].view(dtype='<u2')
             s[pos:pos + 4] = get_style_bits(data=True)
diff --git a/atrcopy/segments.py b/atrcopy/segments.py
index f81e83f..923c5c1 100644
--- a/atrcopy/segments.py
+++ b/atrcopy/segments.py
@@ -858,14 +858,14 @@ class DefaultSegment(object):
         for where_index, comment in zip(indexes, comments):
             rawindex = self.get_raw_index(where_index)
             if comment:
-                log.debug("  restoring comment: rawindex=%d, '%s'" % (rawindex, comment))
+                if _dbg: log.debug("  restoring comment: rawindex=%d, '%s'" % (rawindex, comment))
                 self.rawdata.extra.comments[rawindex] = comment
             else:
                 try:
                     del self.rawdata.extra.comments[rawindex]
-                    log.debug("  no comment in original data, removed comment in current data at rawindex=%d" % rawindex)
+                    if _dbg: log.debug("  no comment in original data, removed comment in current data at rawindex=%d" % rawindex)
                 except KeyError:
-                    log.debug("  no comment in original data or current data at rawindex=%d" % rawindex)
+                    if _dbg: log.debug("  no comment in original data or current data at rawindex=%d" % rawindex)
                     pass
 
     def get_comments_at_indexes(self, indexes):
@@ -888,17 +888,17 @@ class DefaultSegment(object):
         """
         restore_data = []
         for start, end in ranges:
-            log.debug("range: %d-%d" % (start, end))
+            if _dbg: log.debug("range: %d-%d" % (start, end))
             styles = self.style[start:end].copy()
             items = {}
             for i in range(start, end):
                 rawindex = self.get_raw_index(i)
                 try:
                     comment = self.rawdata.extra.comments[rawindex]
-                    log.debug("  index: %d rawindex=%d '%s'" % (i, rawindex, comment))
+                    if _dbg: log.debug("  index: %d rawindex=%d '%s'" % (i, rawindex, comment))
                     items[i] = (rawindex, comment)
                 except KeyError:
-                    log.debug("  index: %d rawindex=%d NO COMMENT TO SAVE" % (i, rawindex))
+                    if _dbg: log.debug("  index: %d rawindex=%d NO COMMENT TO SAVE" % (i, rawindex))
                     items[i] = (rawindex, None)
 
             restore_data.append((start, end, styles, items))
@@ -908,20 +908,20 @@ class DefaultSegment(object):
         """Restore comment styles and data
         """
         for start, end, styles, items in restore_data:
-            log.debug("range: %d-%d" % (start, end))
+            if _dbg: log.debug("range: %d-%d" % (start, end))
             self.style[start:end] = styles
             for i in range(start, end):
                 rawindex, comment = items[i]
                 if comment:
-                    log.debug("  restoring comment: rawindex=%d, '%s'" % (rawindex, comment))
+                    if _dbg: log.debug("  restoring comment: rawindex=%d, '%s'" % (rawindex, comment))
                     self.rawdata.extra.comments[rawindex] = comment
                 else:
                     # no comment in original data, remove any if exists
                     try:
                         del self.rawdata.extra.comments[rawindex]
-                        log.debug("  no comment in original data, removed comment in current data at rawindex=%d" % rawindex)
+                        if _dbg: log.debug("  no comment in original data, removed comment in current data at rawindex=%d" % rawindex)
                     except KeyError:
-                        log.debug("  no comment in original data or current data at rawindex=%d" % rawindex)
+                        if _dbg: log.debug("  no comment in original data or current data at rawindex=%d" % rawindex)
                         pass
 
     def get_comments_in_range(self, start, end):
diff --git a/atrcopy/spartados.py b/atrcopy/spartados.py
index 04eb910..87f11eb 100644
--- a/atrcopy/spartados.py
+++ b/atrcopy/spartados.py
@@ -89,7 +89,7 @@ class SpartaDosDirent(AtariDosDirent):
 
     def start_read(self, image):
         if not self.is_sane:
-            log.debug("Invalid directory entry '%s', starting_sector=%s" % (str(self), self.starting_sector))
+            if _dbg: log.debug("Invalid directory entry '%s', starting_sector=%s" % (str(self), self.starting_sector))
             raise InvalidDirent("Invalid directory entry '%s'" % str(self))
         self.sector_map = image.get_sector_map(self.starting_sector)
         self.sector_map_index = 0
diff --git a/atrcopy/utils.py b/atrcopy/utils.py
index c112737..0307379 100644
--- a/atrcopy/utils.py
+++ b/atrcopy/utils.py
@@ -176,7 +176,7 @@ class Directory(BaseSectorList):
 
     def set(self, index, dirent):
         self.dirents[index] = dirent
-        log.debug("set dirent #%d: %s" % (index, dirent))
+        if _dbg: log.debug("set dirent #%d: %s" % (index, dirent))
 
     def get_free_dirent(self):
         used = set()
@@ -240,10 +240,10 @@ class Directory(BaseSectorList):
         current = 0
         for index, dirent in d:
             for missing in range(current, index):
-                log.debug("Encoding empty dirent at %d" % missing)
+                if _dbg: log.debug("Encoding empty dirent at %d" % missing)
                 data = self.encode_empty()
                 self.store_encoded(data)
-            log.debug("Encoding dirent: %s" % dirent)
+            if _dbg: log.debug("Encoding dirent: %s" % dirent)
             data = self.encode_dirent(dirent)
             self.store_encoded(data)
             current = index + 1
@@ -260,7 +260,7 @@ class Directory(BaseSectorList):
 
     def store_encoded(self, data):
         while True:
-            log.debug("store_encoded: %d bytes in %s" % (len(data), self.current_sector))
+            if _dbg: log.debug("store_encoded: %d bytes in %s" % (len(data), self.current_sector))
             data = self.current_sector.add_data(data)
             if len(data) > 0:
                 self.sectors.append(self.current_sector)
@@ -329,7 +329,7 @@ class VTOC(BaseSectorList):
         order = []
         for i in range(num):
             order.append(self.get_next_free_sector())
-        log.debug("Sectors reserved: %s" % order)
+        if _dbg: log.debug("Sectors reserved: %s" % order)
         self.calc_bitmap()
         return order
 
@@ -337,7 +337,7 @@ class VTOC(BaseSectorList):
         free = np.nonzero(self.sector_map)[0]
         if len(free) > 0:
             num = free[0]
-            log.debug("Found sector %d free" % num)
+            if _dbg: log.debug("Found sector %d free" % num)
             self.sector_map[num] = 0
             return num
         raise NotEnoughSpaceOnDisk("No space left in VTOC")
diff --git a/test/mock.py b/test/mock.py
index 397fc21..90324ba 100644
--- a/test/mock.py
+++ b/test/mock.py
@@ -26,5 +26,8 @@ logging.basicConfig(level=logging.WARNING)
 logger = logging.getLogger()
 logger.setLevel(logging.DEBUG)
 
+import __builtin__
+__builtin__._dbg = False
+
 import numpy as np
 from numpy.testing import assert_almost_equal
diff --git a/test/test_add_file.py b/test/test_add_file.py
index 1a2652e..3895aa6 100644
--- a/test/test_add_file.py
+++ b/test/test_add_file.py
@@ -159,6 +159,9 @@ class TestDos33Image(BaseFilesystemModifyTest):
 
 
 if __name__ == "__main__":
+    import __builtin__
+    __builtin__._dbg = False
+
     t = TestAtariDosSDImage()
     for name in dir(t):
         print name