diff --git a/igor/struct.py b/igor/struct.py
index a50ede5..0821109 100644
--- a/igor/struct.py
+++ b/igor/struct.py
@@ -433,7 +433,7 @@ class Structure (_struct.Struct):
 
     You can also read out from strings:
 
-    >>> d = experiment.unpack(b.tostring())
+    >>> d = experiment.unpack(b.tobytes())
     >>> pprint(d)
     {'runs': [{'data': array([[1543, 2057, 2571],
            [3085, 3599, 4113]]),
@@ -447,9 +447,9 @@ class Structure (_struct.Struct):
     values are filled in with their defaults.
 
     >>> experiment.pack_into(buffer=b, data=d)
-    >>> b.tostring()[:17]
+    >>> b.tobytes()[:17]
     '\x00\x01\x02\x03\x04\x05\x06\x07\x08\t\n\x0b\x0c\r\x0e\x0f\x10'
-    >>> b.tostring()[17:]
+    >>> b.tobytes()[17:]
     '\x11\x12\x13\x14\x15\x16\x17\x18\x19\x1a\x1b\x1c\x1d\x1e\x1f !'
     >>> run0 = d['runs'].pop(0)
     >>> b = experiment.pack(data=d)
diff --git a/igor/util.py b/igor/util.py
index ecc783a..5a70db0 100644
--- a/igor/util.py
+++ b/igor/util.py
@@ -51,7 +51,7 @@ def hex_bytes(buffer, spaces=None):
     hex_bytes = ['{:02x}'.format(_ord(x)) for x in buffer]
     if spaces is None:
         return ''.join(hex_bytes)
-    elif spaces is 1:
+    elif spaces == 1:
         return ' '.join(hex_bytes)
     for i in range(len(hex_bytes)//spaces):
         hex_bytes.insert((spaces+1)*(i+1)-1, ' ')