redo attempt at tutorial checking to use md5 checksums instead. depen…

…ds on pydata/xarray-data#9

xarray/tutorial.py

@@ -9,6 +9,8 @@
 from __future__ import division
 from __future__ import print_function
 
+import hashlib
+
 import os as _os
 import shutil as _shutil
 
@@ -19,9 +21,17 @@
 _default_cache_dir = _os.sep.join(('~', '.xarray_tutorial_data'))
 
 
+def _md5(fname):
+    hash_md5 = hashlib.md5()
+    with open(fname, "rb") as f:
+        hash_md5.update(f.read())
+    return hash_md5.hexdigest()
+
+
 # idea borrowed from Seaborn
 def load_dataset(name, cache=True, cache_dir=_default_cache_dir,
-                 github_url='https://github.com/pydata/xarray-data',  **kws):
+                 github_url='https://github.com/pydata/xarray-data',
+                 branch='master', **kws):
     """
     Load a dataset from the online repository (requires internet).
 
@@ -38,32 +48,39 @@ def load_dataset(name, cache=True, cache_dir=_default_cache_dir,
         If True, then cache data locally for use on subsequent calls
     github_url : string
         Github repository where the data is stored
+    branch : string
+        The git branch to download from
     kws : dict, optional
         Passed to xarray.open_dataset
 
     """
     longdir = _os.path.expanduser(cache_dir)
-    tmpdir = _os.sep.join((longdir, '.tmp'))
     fullname = name + '.nc'
     localfile = _os.sep.join((longdir, fullname))
-    tmpfile = _os.sep.join((longdir, fullname))
+    md5name = name + '.md5'
+    md5file = _os.sep.join((longdir, md5name))
 
     if not _os.path.exists(localfile):
 
         # This will always leave this directory on disk.
         # May want to add an option to remove it.
         if not _os.path.isdir(longdir):
             _os.mkdir(longdir)
-        if not _os.path.isdir(tmpdir):
-            _os.mkdir(tmpdir)
-
-        url = '/'.join((github_url, 'raw', 'master', fullname))
-        _urlretrieve(url, tmpfile)
-
-        if not _os.path.exists(tmpfile):
-            raise ValueError('File could not be downloaded, please try again')
 
-        _shutil.move(tmpfile, localfile)
+        url = '/'.join((github_url, 'raw', branch, fullname))
+        _urlretrieve(url, localfile)
+        url = '/'.join((github_url, 'raw', branch, md5name))
+        _urlretrieve(url, md5file)
+
+        localmd5 = _md5(localfile)
+        with open(md5file, 'r') as f:
+            remotemd5 = f.read()
+        if localmd5 != remotemd5:
+            _os.remove(localfile)
+            msg = """
+            MD5 checksum does not match, try downloading dataset again.
+            """
+            raise IOError(msg)
 
     ds = _open_dataset(localfile, **kws).load()