diff --git a/docs/misc.rst b/docs/misc.rst
index 0c2f2b1..8f7bb4a 100644
--- a/docs/misc.rst
+++ b/docs/misc.rst
@@ -89,3 +89,15 @@ Miscellanea
     >>> foo()
     >>> foo()
     >>>
+
+
+.. py:function:: pydu.misc.super_len(obj)
+
+    Get length of object which has attribute named `__len__`, `len`, `fileno`, `tell`,
+    such as `list`, `tuple`, `dict`, `file` and so on.
+
+    >>> from pydu.misc import super_len
+    >>> super_len([1, 2])
+    2
+    >>> super_len(open('test', 'w'))
+    0
diff --git a/pydu/misc.py b/pydu/misc.py
index 8a43dee..ccce52b 100644
--- a/pydu/misc.py
+++ b/pydu/misc.py
@@ -162,27 +162,27 @@ def memoize_when_activated(fun):
 
 
 # https://github.com/requests/requests/blob/master/requests/utils.py
-def super_len(o):
+def super_len(obj):
     total_length = None
     current_position = 0
 
-    if hasattr(o, '__len__'):
-        total_length = len(o)
+    if hasattr(obj, '__len__'):
+        total_length = len(obj)
 
-    elif hasattr(o, 'len'):
-        total_length = o.len
+    elif hasattr(obj, 'len'):
+        total_length = obj.len
 
-    elif hasattr(o, 'fileno'):
+    elif hasattr(obj, 'fileno'):
         try:
-            fileno = o.fileno()
+            fileno = obj.fileno()
         except io.UnsupportedOperation:
             pass
         else:
             total_length = os.fstat(fileno).st_size
 
-    if hasattr(o, 'tell'):
+    if hasattr(obj, 'tell'):
         try:
-            current_position = o.tell()
+            current_position = obj.tell()
         except (OSError, IOError):
             # This can happen in some weird situations, such as when the file
             # is actually a special file descriptor like stdin. In this
@@ -191,16 +191,16 @@ def super_len(o):
             if total_length is not None:
                 current_position = total_length
         else:
-            if hasattr(o, 'seek') and total_length is None:
+            if hasattr(obj, 'seek') and total_length is None:
                 # StringIO and BytesIO have seek but no useable fileno
                 try:
                     # seek to end of file
-                    o.seek(0, 2)
-                    total_length = o.tell()
+                    obj.seek(0, 2)
+                    total_length = obj.tell()
 
                     # seek back to current position to support
                     # partially read file-like objects
-                    o.seek(current_position or 0)
+                    obj.seek(current_position or 0)
                 except (OSError, IOError):
                     total_length = 0