diff --git a/include/boost/histogram/detail/meta.hpp b/include/boost/histogram/detail/meta.hpp
index c8d15700..79a3edc6 100644
--- a/include/boost/histogram/detail/meta.hpp
+++ b/include/boost/histogram/detail/meta.hpp
@@ -49,6 +49,12 @@ template <typename T,
                               std::end(std::declval<T&>()))>
 struct is_sequence {};
 
+struct histogram_tag {};
+
+template <typename T,
+          typename = typename T::histogram_tag>
+struct is_histogram {};
+
 template <typename S1,
           typename S2>
 struct intersection {
diff --git a/include/boost/histogram/detail/variance.hpp b/include/boost/histogram/detail/variance.hpp
index d4f549e0..8388ee53 100644
--- a/include/boost/histogram/detail/variance.hpp
+++ b/include/boost/histogram/detail/variance.hpp
@@ -13,14 +13,10 @@ namespace boost {
 namespace histogram {
 namespace detail {
 
-// standard Poisson estimate
-template <typename Value>
-Value variance(Value k) { return k; }
-
 namespace {
   template <typename Storage>
   typename std::enable_if<
-    (has_weight_support<Storage>::value),
+    has_weight_support<Storage>::value,
     typename Storage::value_type
   >::type
   variance_impl(const Storage& s, std::size_t i)
@@ -32,7 +28,7 @@ namespace {
     typename Storage::value_type
   >::type
   variance_impl(const Storage& s, std::size_t i)
-  { return variance(s.value(i)); }
+  { return s.value(i); } // standard Poisson estimate
 }
 
 template <typename Storage>
diff --git a/include/boost/histogram/dynamic_histogram.hpp b/include/boost/histogram/dynamic_histogram.hpp
index d928c0c2..0fd7e4f6 100644
--- a/include/boost/histogram/dynamic_histogram.hpp
+++ b/include/boost/histogram/dynamic_histogram.hpp
@@ -13,12 +13,11 @@
 #include <boost/mpl/empty.hpp>
 #include <boost/variant.hpp>
 #include <boost/histogram/axis.hpp>
-#include <boost/histogram/utility.hpp>
+#include <boost/histogram/storage/adaptive_storage.hpp>
 #include <boost/histogram/detail/meta.hpp>
 #include <boost/histogram/detail/utility.hpp>
 #include <boost/histogram/detail/variance.hpp>
 #include <boost/histogram/detail/axis_visitor.hpp>
-#include <boost/histogram/storage/adaptive_storage.hpp>
 #include <cstddef>
 #include <vector>
 #include <type_traits>
@@ -35,9 +34,12 @@ class dynamic_histogram
   static_assert(!mpl::empty<Axes>::value, "at least one axis required");
 
 public:
+  using histogram_tag = detail::histogram_tag;
   using axis_type = typename make_variant_over<Axes>::type;
-  using axes_type = std::vector<axis_type>;
   using value_type = typename Storage::value_type;
+private:
+  using axes_type = std::vector<axis_type>;
+public:
 
   dynamic_histogram() = default;
 
@@ -275,8 +277,6 @@ public:
     return axes_[N];
   }
 
-  const axes_type& axes() const { return axes_; }
-
 private:
   axes_type axes_;
   Storage storage_;
@@ -322,11 +322,14 @@ private:
     }
   }
 
+  friend struct storage_access;
+
+  template <class OtherStorage, class OtherAxes, class Visitor>
+  friend void for_each_axis(const dynamic_histogram<OtherStorage, OtherAxes>&, Visitor&);
+
   template <typename OtherAxes, typename OtherStorage>
   friend class dynamic_histogram;
 
-  friend struct storage_access;
-
   template <typename Archiv, typename OtherAxes, typename OtherStorage>
   friend void serialize(Archiv&, dynamic_histogram<OtherAxes, OtherStorage>&, unsigned);
 };
diff --git a/include/boost/histogram/histogram_ostream_operators.hpp b/include/boost/histogram/histogram_ostream_operators.hpp
index 59d542ab..6938cb4a 100644
--- a/include/boost/histogram/histogram_ostream_operators.hpp
+++ b/include/boost/histogram/histogram_ostream_operators.hpp
@@ -7,14 +7,10 @@
 #ifndef _BOOST_HISTOGRAM_HISTOGRAM_STREAMER_HPP_
 #define _BOOST_HISTOGRAM_HISTOGRAM_STREAMER_HPP_
 
-#include <boost/histogram/axis.hpp>
 #include <boost/histogram/axis_ostream_operators.hpp>
 #include <boost/histogram/static_histogram.hpp>
 #include <boost/histogram/dynamic_histogram.hpp>
-#include <boost/fusion/algorithm/iteration/for_each.hpp>
-#include <boost/fusion/include/for_each.hpp>
-#include <boost/variant/static_visitor.hpp>
-#include <boost/variant/apply_visitor.hpp>
+#include <boost/histogram/utility.hpp>
 #include <ostream>
 
 namespace boost {
@@ -30,23 +26,13 @@ namespace detail {
   };
 }
 
-template <typename Axes, typename Storage>
-inline std::ostream& operator<<(std::ostream& os, const static_histogram<Axes, Storage>& h)
+template <template <typename, typename> typename Histogram, typename Axes, typename Storage,
+          typename = detail::is_histogram<Histogram<Axes, Storage>>>
+inline std::ostream& operator<<(std::ostream& os, const Histogram<Axes, Storage>& h)
 {
     os << "histogram(";
     detail::axis_ostream_visitor sh(os);
-    fusion::for_each(h.axes(), sh);
-    os << (h.dim() ? "\n)" : ")");
-    return os;
-}
-
-template <typename Axes, typename Storage>
-inline std::ostream& operator<<(std::ostream& os, const dynamic_histogram<Axes, Storage>& h)
-{
-    os << "histogram(";
-    detail::axis_ostream_visitor sh(os);
-    for (const auto& a : h.axes())
-        apply_visitor(sh, a);
+    for_each_axis(h, sh);
     os << (h.dim() ? "\n)" : ")");
     return os;
 }
diff --git a/include/boost/histogram/static_histogram.hpp b/include/boost/histogram/static_histogram.hpp
index 2a45505c..453b38a8 100644
--- a/include/boost/histogram/static_histogram.hpp
+++ b/include/boost/histogram/static_histogram.hpp
@@ -21,10 +21,10 @@
 #include <boost/fusion/container/vector/convert.hpp>
 #include <boost/fusion/include/as_vector.hpp>
 #include <boost/histogram/axis.hpp>
+#include <boost/histogram/storage/adaptive_storage.hpp>
 #include <boost/histogram/detail/meta.hpp>
 #include <boost/histogram/detail/variance.hpp>
 #include <boost/histogram/detail/axis_visitor.hpp>
-#include <boost/histogram/storage/adaptive_storage.hpp>
 #include <type_traits>
 
 namespace boost {
@@ -36,8 +36,11 @@ class static_histogram
   static_assert(!mpl::empty<Axes>::value, "at least one axis required");
 
 public:
-  using axes_type = typename fusion::result_of::as_vector<Axes>::type;
+  using histogram_tag = detail::histogram_tag;
   using value_type = typename Storage::value_type;
+private:
+  using axes_type = typename fusion::result_of::as_vector<Axes>::type;
+public:
 
   static_histogram() = default;
 
@@ -257,8 +260,6 @@ public:
     return fusion::at_c<N>(axes_);
   }
 
-  const axes_type& axes() const { return axes_; }
-
 private:
   axes_type axes_;
   Storage storage_;
@@ -310,6 +311,9 @@ private:
     static void apply(Linearize&, const axes_type&, Iterator) {}
   };
 
+  template <class OtherStorage, class OtherAxes, class Visitor>
+  friend void for_each_axis(const static_histogram<OtherStorage, OtherAxes>&, Visitor&);
+
   template <typename OtherAxes, typename OtherStorage>
   friend class static_histogram;
 
diff --git a/include/boost/histogram/storage/adaptive_storage.hpp b/include/boost/histogram/storage/adaptive_storage.hpp
index 44261fa7..459efd2a 100644
--- a/include/boost/histogram/storage/adaptive_storage.hpp
+++ b/include/boost/histogram/storage/adaptive_storage.hpp
@@ -499,12 +499,12 @@ adaptive_storage<Allocator>::variance(std::size_t i) const
 {
   switch (buffer_.type_.id_) {
     case 0: break;
-    case 1: return detail::variance(buffer_.template at<uint8_t> (i));
-    case 2: return detail::variance(buffer_.template at<uint16_t>(i));
-    case 3: return detail::variance(buffer_.template at<uint32_t>(i));
-    case 4: return detail::variance(buffer_.template at<uint64_t>(i));
+    case 1: return buffer_.template at<uint8_t> (i);
+    case 2: return buffer_.template at<uint16_t>(i);
+    case 3: return buffer_.template at<uint32_t>(i);
+    case 4: return buffer_.template at<uint64_t>(i);
     case 5: return static_cast<value_type>(
-      detail::variance(buffer_.template at<detail::mp_int>(i))
+      buffer_.template at<detail::mp_int>(i)
     );
     case 6: return buffer_.template at<detail::weight>(i).w2;
   }
diff --git a/include/boost/histogram/utility.hpp b/include/boost/histogram/utility.hpp
index a0cca3e6..2666300f 100644
--- a/include/boost/histogram/utility.hpp
+++ b/include/boost/histogram/utility.hpp
@@ -9,6 +9,10 @@
 
 #include <boost/variant.hpp>
 #include <boost/histogram/detail/axis_visitor.hpp>
+#include <boost/fusion/algorithm/iteration/for_each.hpp>
+#include <boost/fusion/include/for_each.hpp>
+#include <boost/histogram/static_histogram.hpp>
+#include <boost/histogram/dynamic_histogram.hpp>
 
 namespace boost {
 namespace histogram {
@@ -56,6 +60,19 @@ template <typename... Axes>
 double center(const boost::variant<Axes...>& a, const int i)
 { return apply_visitor(detail::center(i), a); }
 
+template <typename Storage, typename Axes, typename Visitor>
+void for_each_axis(const static_histogram<Storage, Axes>& h, Visitor& visitor)
+{
+  fusion::for_each(h.axes_, visitor);
+}
+
+template <typename Storage, typename Axes, typename Visitor>
+void for_each_axis(const dynamic_histogram<Storage, Axes>& h, Visitor& visitor)
+{
+  for (const auto& a : h.axes_)
+    apply_visitor(visitor, a);
+}
+
 }
 }
 
diff --git a/src/python/histogram.cpp b/src/python/histogram.cpp
index 697fc3fc..57b0589f 100644
--- a/src/python/histogram.cpp
+++ b/src/python/histogram.cpp
@@ -57,7 +57,7 @@ histogram_init(python::tuple args, python::dict kwargs) {
   const unsigned dim = len(args) - 1;
 
   // normal constructor
-  dynamic_histogram<>::axes_type axes;
+  std::vector<dynamic_histogram<>::axis_type> axes;
   for (unsigned i = 0; i < dim; ++i) {
     object pa = args[i + 1];
     extract<regular_axis<>> er(pa);
@@ -75,7 +75,8 @@ histogram_init(python::tuple args, python::dict kwargs) {
     PyErr_SetString(PyExc_TypeError, msg.c_str());
     throw_error_already_set();
   }
-  return pyinit(axes.begin(), axes.end());
+  dynamic_histogram<> h(axes.begin(), axes.end());
+  return pyinit(h);
 }
 
 python::object
@@ -306,9 +307,6 @@ void register_histogram()
   using python::arg;
   docstring_options dopt(true, true, false);
 
-  // used to pass arguments from raw python init to specialized C++ constructor
-  class_<dynamic_histogram<>::axes_type::iterator>("axes_iterator", no_init);
-
   class_<dynamic_histogram<>, boost::shared_ptr<dynamic_histogram<>>>("histogram",
     "N-dimensional histogram for real-valued data.",
     no_init)
@@ -317,8 +315,7 @@ void register_histogram()
        "\nPass one or more axis objects to define"
        "\nthe dimensions of the dynamic_histogram<>.")
     // shadowed C++ ctors
-    .def(init<dynamic_histogram<>::axes_type::iterator,
-              dynamic_histogram<>::axes_type::iterator>())
+    .def(init<const dynamic_histogram<>&>())
     .add_property("__array_interface__",
         &storage_access::array_interface)
     .add_property("dim", &dynamic_histogram<>::dim,