RF - promote guessed_endian to public classmethod

Guessed endian needs to be written for each substantial subclass, so it
should be part of the API.  It makes more sense as a classmethod because
we should not need an instance to test other data for endianness.

Author: matthew-brett

nibabel/analyze.py

@@ -245,7 +245,8 @@ def __init__(self,
         '''
         super(AnalyzeHeader, self).__init__(binaryblock, endianness, check)
 
-    def _guessed_endian(self, hdr):
+    @classmethod
+    def guessed_endian(klass, hdr):
         ''' Guess intended endianness from mapping-like ``hdr``
 
         Parameters
@@ -264,19 +265,19 @@ def _guessed_endian(self, hdr):
 
         >>> hdr = AnalyzeHeader()
         >>> hdr_data = np.zeros((), dtype=header_dtype)
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
 
         A valid native header is guessed native
 
         >>> hdr_data = hdr.structarr.copy()
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
 
         And, when swapped, is guessed as swapped
 
         >>> sw_hdr_data = hdr_data.byteswap(swapped_code)
-        >>> hdr._guessed_endian(sw_hdr_data) == swapped_code
+        >>> AnalyzeHeader.guessed_endian(sw_hdr_data) == swapped_code
         True
 
         The algorithm is as follows:
@@ -287,13 +288,13 @@ def _guessed_endian(self, hdr):
 
         >>> hdr_data = np.zeros((), dtype=header_dtype) # blank binary data
         >>> hdr_data['dim'][0] = 1
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
         >>> hdr_data['dim'][0] = 6
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
         >>> hdr_data['dim'][0] = -1
-        >>> hdr._guessed_endian(hdr_data) == swapped_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == swapped_code
         True
 
         If the first ``dim`` value is zeros, we need a tie breaker.
@@ -302,20 +303,20 @@ def _guessed_endian(self, hdr):
         assumed swapped.  Otherwise assume native.
 
         >>> hdr_data = np.zeros((), dtype=header_dtype) # blank binary data
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
         >>> hdr_data['sizeof_hdr'] = 1543569408
-        >>> hdr._guessed_endian(hdr_data) == swapped_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == swapped_code
         True
         >>> hdr_data['sizeof_hdr'] = -1
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
 
         This is overridden by the ``dim``[0] value though:
 
         >>> hdr_data['sizeof_hdr'] = 1543569408
         >>> hdr_data['dim'][0] = 1
-        >>> hdr._guessed_endian(hdr_data) == native_code
+        >>> AnalyzeHeader.guessed_endian(hdr_data) == native_code
         True
         '''
         dim0 = int(hdr['dim'][0])

nibabel/tests/test_wrapstruct.py

@@ -11,8 +11,8 @@
 This is a root testing class, used in the Analyze and other tests as a
 framework for all the tests common to the Analyze types
 
-Refactoring TODO
-----------------
+Refactoring TODO maybe
+----------------------
 
 binaryblock
 diagnose_binaryblock
@@ -21,7 +21,6 @@
 
 With deprecation warnings
 
-_guessed_endian -> guessed_endian
 _field_recoders -> field_recoders
 '''
 import logging
@@ -53,7 +52,8 @@ class MyWrapStruct(WrapStruct):
         ('a_str', 'S10')]
     _dtype = np.dtype(dtype_def)
 
-    def _guessed_endian(self, hdr):
+    @classmethod
+    def guessed_endian(klass, hdr):
         if hdr['an_integer'] < 256:
             return native_code
         return swapped_code

nibabel/wrapstruct.py

@@ -155,7 +155,7 @@ def __init__(self,
                          dtype=self._dtype,
                          buffer=binaryblock)
         if endianness is None:
-            endianness = self._guessed_endian(wstr)
+            endianness = self.__class__.guessed_endian(wstr)
         else:
             endianness = endian_codes[endianness]
         if endianness != native_code:
@@ -352,13 +352,15 @@ def diagnose_binaryblock(klass, binaryblock, endianness=None):
         return '\n'.join([report.message
                           for report in reports if report.message])
 
-    def _guessed_endian(self, wstr):
-        ''' Guess intended endianness from mapping-like ``wstr``
+    @classmethod
+    def guessed_endian(self, mapping):
+        ''' Guess intended endianness from mapping-like ``mapping``
 
         Parameters
         ----------
         wstr : mapping-like
-           wstr for which to guess endianness
+            Something implementing a mapping.  We will guess the endianness from
+            looking at the field values
 
         Returns
         -------