Improved portability between Python 2 and Python 3. Beginnings of code for writing SEG Y.

portability.py

@@ -1,4 +1,7 @@
 import os
+import sys
+
+EMPTY_BYTE_STRING = b'' if sys.version_info >= (3, 0) else ''
 
 
 def seekable(fh):
@@ -21,4 +24,31 @@ def seekable(fh):
                 fh.seek(pos)
         except AttributeError:
             return False
-    return True
+    return True
+
+
+if sys.version_info >= (3, 0):
+    long_int = int
+else:
+    long_int = long
+
+
+if sys.version_info >= (3, 0):
+    def byte_string(integers):
+        return bytes(integers)
+else:
+    def byte_string(integers):
+        return ''.join(chr(i) for i in integers)
+
+
+if sys.version_info >= (3, 0):
+    import reprlib
+    reprlib = reprlib  # Keep the static analyzer happy
+else:
+    import repr as reprlib
+
+if sys.version_info >= (3, 0):
+    izip = zip
+else:
+    from itertools import izip
+    izip = izip    # Keep the static analyzer happy