Python 3.6 compatibility.

.gitignore

@@ -1,2 +1,3 @@
 build/
 *.pyc
+.tox

CHANGES_FOR_PY36.md

@@ -0,0 +1,53 @@
+odespy/__init__.py
+    enable absolute imports , print function
+    use explicit relative imports
+    try statement around line that deletes variables from locals
+
+odespy/solvers.py
+    enable absolute imports , print function
+    replace all print statements with print function
+    Replaced many "ValueError, msg" to "ValueError(msg)"
+    Mixed spaces and tabs: lines 933-937, 962-967, 1508
+    TypeError, msg to TypeError(msg): 1162
+    ImportError, msg to ImportError(msg): 2014, 2944
+    except Exception as e: 2993
+    "not_valid is not defined error" at 2909
+        apparently in Python 3 list comprehensions like this in class 
+        body can't access variables defined in class body. This works in py2.7.
+        Replaced list comprehension with for loop.
+    in function _format_parameters_table: line 480, convert parameter_names 
+        into list. dict.keys() in PY3 returns dict_list object not list.
+
+odespy/RungeKutta.py
+    enable absolute imports , print function
+    replace all print statements with print function
+    Replaced many "ValueError, msg" to "ValueError(msg)"
+
+odespy/rkc.py
+    enable absolute imports , print function
+    Replaced a few "ValueError, msg" to "ValueError(msg)"
+
+odespy/rkc.py
+    enable absolute imports , print function
+    replace all print statements with print function
+
+odespy/odepack.py
+    enable absolute imports , print function
+    Replaced a few "ValueError, msg" to "ValueError(msg)"
+    replace all print statements with print function
+    mixed tabs and space: 1203, 1232, 1235, 1343, 1456, 1574
+    explicit relative import of _odepack.
+    remove the global apply() function
+
+odespy/radau5.py
+    enable absolute imports , print function
+    print function
+    mixed tab/space: 283
+
+odespy/problems.py
+    enable absolute imports , print function
+    print function
+
+odespy/tests/test_basic.py
+    enable absolute imports , print function
+    many places (example line 89, 90): the lambda syntax is invalid in PY3.6

odespy/RungeKutta.py

@@ -1,4 +1,5 @@
-from solvers import Solver, Adaptive
+from __future__ import absolute_import, print_function
+from . solvers import Solver, Adaptive
 import numpy as np
 
 def _calculate_order_1_level(coefficients):
@@ -134,7 +135,7 @@ def middle(x,y,z):    # Auxilary function
         k = np.zeros((k_len, self.neq), self.dtype)  # intern stages
 
         if self.verbose > 0:
-            print 'advance solution in [%s, %s], h=%g' % (t_n, t_next, h)
+            print('advance solution in [%s, %s], h=%g' % (t_n, t_next, h))
 
         # Loop until next time point is reached
         while (abs(t - t_n) < abs(t_next - t_n)):
@@ -150,7 +151,7 @@ def middle(x,y,z):    # Auxilary function
 
             self.info['rejected'] += 1  # reduced below if accepted
             if self.verbose > 0:
-                print '  u(t=%g)=%g: ' % (t+h, u_new),
+                print('  u(t=%g)=%g: ' % (t+h, u_new)),
 
             # local error between 2 levels
             error = h*np.abs(np.dot(factors_error, k))
@@ -171,18 +172,18 @@ def middle(x,y,z):    # Auxilary function
                 self.info['rejected'] -= 1
 
                 if self.verbose > 0:
-                    print 'accepted, ',
+                    print('accepted, '),
             else:
                 if self.verbose > 0:
-                    print 'rejected, ',
+                    print('rejected, '),
 
             if self.verbose > 0:
-                print 'err=%s, ' % str(error),
+                print('err=%s, ' % str(error)),
                 if hasattr(self, 'u_exact') and callable(self.u_exact):
-                    print 'exact-err=%s, ' % \
-                          (np.asarray(self.u_exact(t+h))-u_new),
+                    print('exact-err=%s, ' %
+                          (np.asarray(self.u_exact(t+h))-u_new)),
                 if h <= self.min_step:
-                    print 'h=min_step!! ',
+                    print('h=min_step!! '),
 
 
            # Replace 0 values by 1e-16 since we will divide by error
@@ -209,7 +210,7 @@ def middle(x,y,z):    # Auxilary function
             h = min(h, t_next - t_intermediate[-1])
 
             if self.verbose > 0:
-                print 'new h=%g' % h
+                print('new h=%g' % h)
 
             if h == 0:
                 break
@@ -367,16 +368,16 @@ def validate_data(self):
         # Check for dimension of user-defined butcher table.
         array_shape = self.butcher_tableau.shape
         if len(array_shape) is not 2:
-            raise ValueError,'''
-        Illegal input! Your input butcher_tableau should be a 2d-array!'''
+            raise ValueError('''
+        Illegal input! Your input butcher_tableau should be a 2d-array!''')
         else:
             m,n = array_shape
             if m not in (n, n + 1):
-                raise ValueError, '''\
+                raise ValueError('''\
         The dimension of 2d-array <method_yours_array> should be:
         1. Either (n, n), --> For 1-level RungeKutta methods
         2. Or (n+1, n),   --> For 2-levels RungeKutta methods
-        The shape of your input array is (%d, %d).''' % (m,n)
+        The shape of your input array is (%d, %d).''' % (m,n))
         self._butcher_tableau = self.butcher_tableau
 
         # Check for user-defined order,
@@ -393,19 +394,19 @@ def validate_data(self):
             if array_shape[0] == array_shape[1] + 1:
                 # 2-level RungeKutta methods
                 if type(self.method_order) is int:
-                    raise ValueError, error_2level
+                    raise ValueError(error_2level)
                 try:
                     order1, order2 = self.method_order
                     if abs(order1-order2) != 1 or \
                             order1 < 1 or order2 < 1:
-                        raise ValueError, error_2level
+                        raise ValueError(error_2level)
                 except:
-                    raise ValueError,error_2level
+                    raise ValueError(error_2level)
             else:
                 # 1-level RungeKutta methods
                 if type(self.method_order) is not int or \
                         self.method_order < 1:
-                    raise ValueError,error_1level
+                    raise ValueError(error_1level)
             self._method_order = self.method_order
 
         else:   # method_order is not specified
@@ -418,14 +419,14 @@ def validate_data(self):
         for i in range(1,array_shape[1] - 1):
             if not np.allclose(self.butcher_tableau[i][0],\
                                sum(self.butcher_tableau[i][1:])):
-                raise ValueError, '''
+                raise ValueError('''
         Inconsistent data in Butcher_Tableau!
         In each lines of stage-coefficients, first number should be
         equal to the sum of other numbers.
         That is, for a butcher_table with K columns,
             a[i][0] == a[i][1] + a[i][2] + ... + a[i][K - 1]
             where 1 <= i <= K - 1
         Your input for line %d is :%s
-        ''' % (i,str(self.butcher_tableau[i]))
+        ''' % (i,str(self.butcher_tableau[i])))
 
         return True

odespy/__init__.py

@@ -5,6 +5,7 @@
 supported.  A wide range of numerical methods for ODEs are offered:
 
 """
+from __future__ import absolute_import, print_function
 
 # Insert tutorial from ../doc/src/odespy/odespy.rst
 
@@ -1254,14 +1255,13 @@ def f(u, t):
 The file `logistic10.py <https://github.com/hplgit/odespy/blob/master/doc/src/odespy/src-odespy/logistic10.py>`_ contains a complete program for solving the logistic ODE
 with :math:`f(u,t)` implemented in Fortran.
 '''
-
-from solvers import *
-from RungeKutta import *
-from rkc import *
-from rkf45 import *
-from odepack import *
-from radau5 import *
-import problems
+from . solvers import *
+from . RungeKutta import *
+from . rkc import *
+from . rkf45 import *
+from . odepack import *
+from . radau5 import *
+from . import problems
 
 # Update doc strings with common info
 class_, doc_str, classname = None, None, None
@@ -1282,8 +1282,13 @@ def f(u, t):
 __doc__ =  __doc__ + typeset_toc(toc) + _tutorial
 
 # Do not pollute namespace
-del class_, doc_str, classname, classnames, toc, typeset_toc, \
-    table_of_parameters, name, obj, inspect
+try:
+    del class_, doc_str, classname, classnames, toc, typeset_toc, \
+        table_of_parameters, name, obj, inspect
+except NameError:
+    # the var 'name' is used in a list compression, which is leaked into
+    # locals in PY2 but not in Py3 (at-least py3.6).
+    pass
 
 if __name__ == '__main__':
     from os.path import join