Merge pull request #1158 from takluyver/nbpy-encoding-declaration

Add coding header when notebook exported to .py file.

Closes gh-1156, also strips the encoding declaration out when we load a .py file.

IPython/nbformat/v2/nbpy.py

@@ -16,6 +16,7 b' Authors:'
 # Imports
 #-----------------------------------------------------------------------------
 
+import re
 from .rwbase import NotebookReader, NotebookWriter
 from .nbbase import new_code_cell, new_text_cell, new_worksheet, new_notebook
 
@@ -23,6 +24,8 b' from .nbbase import new_code_cell, new_text_cell, new_worksheet, new_notebook'
 # Code
 #-----------------------------------------------------------------------------
 
+_encoding_declaration_re = re.compile(r"^#.*coding[:=]\s*([-\w.]+)")
+
 class PyReaderError(Exception):
     pass
 
@@ -38,7 +41,7 b' class PyReader(NotebookReader):'
         cell_lines = []
         state = u'codecell'
         for line in lines:
-            if line.startswith(u'# <nbformat>'):
+            if line.startswith(u'# <nbformat>') or _encoding_declaration_re.match(line):
                 pass
             elif line.startswith(u'# <codecell>'):
                 cell = self.new_cell(state, cell_lines)
@@ -110,7 +113,7 b' class PyReader(NotebookReader):'
 class PyWriter(NotebookWriter):
 
     def writes(self, nb, **kwargs):
-        lines = []
+        lines = [u'# -*- coding: utf-8 -*-']
         lines.extend([u'# <nbformat>2</nbformat>',''])
         for ws in nb.worksheets:
             for cell in ws.cells:

IPython/nbformat/v2/tests/nbexamples.py

@@ -81,7 +81,8 b' nb0 = new_notebook('
     metadata=md
 )
 
-nb0_py = """# <nbformat>2</nbformat>
+nb0_py = """# -*- coding: utf-8 -*-
+# <nbformat>2</nbformat>
 
 # <htmlcell>