Add Beatles introduction

lod/helpers.py

@@ -1,12 +1,22 @@
+'''
+Helper functions and ipython magic for the SPARQL exercises.
+
+The tests in the notebooks rely on the `LAST_QUERY` variable, which is updated by the `%%sparql` magic after every query.
+This variable contains the full query used (`LAST_QUERY["query"]`), the endpoint it was sent to (`LAST_QUERY["endpoint"]`), and a dictionary with the response of the endpoint (`LAST_QUERY["results"]`).
+For convenience, the results are also given as tuples (`LAST_QUERY["tuples"]`), and as a dictionary of of `{column:[values]}` (`LAST_QUERY["columns"]`).
+'''
 from IPython.core.magic import (register_line_magic, register_cell_magic,
                                 register_line_cell_magic)
-
-from IPython.display import HTML, display, Image
+from IPython.display import HTML, display, Image, display_javascript
 from urllib.request import Request, urlopen
 from urllib.parse import quote_plus, urlencode
 from urllib.error import HTTPError
 
 import json
+import sys
+
+js = "IPython.CodeCell.options_default.highlight_modes['magic_sparql'] = {'reg':[/^%%sparql/]};"
+display_javascript(js, raw=True)
 
 
 def send_query(query, endpoint):
@@ -20,7 +30,11 @@ def send_query(query, endpoint):
                 headers={'content-type': 'application/x-www-form-urlencoded',
                          'accept': FORMATS},
                 method='POST')
-    return json.loads(urlopen(r).read().decode('utf-8'));
+    res = urlopen(r)
+    data = res.read().decode('utf-8')
+    if res.getcode() == 200:
+        return json.loads(data)
+    raise Exception('Error getting results: {}'.format(data))
 
 
 def tabulate(tuples, header=None):
@@ -39,11 +53,14 @@ def tabulate(tuples, header=None):
 
 LAST_QUERY = {}
 
+def solution():
+    return LAST_QUERY
+
 
 def query(query, endpoint=None, print_table=False):
     global LAST_QUERY
 
-    endpoint = endpoint or "http://dbpedia.org/sparql"
+    endpoint = endpoint or "http://fuseki.cluster.gsi.dit.upm.es/sitc/"
     results = send_query(query, endpoint)
     tuples = to_table(results)
 
@@ -80,12 +97,30 @@ def to_table(results):
 
 @register_cell_magic
 def sparql(line, cell):
+    '''
+    Sparql magic command for ipython. It can be used in a cell like this:
+    
+    ```
+    %%sparql
+    
+    ... Your SPARQL query ...
+    
+    ```
+    
+    by default, it will use the DBpedia endpoint, but you can use a different endpoint like this:
+    
+    ```
+    %%sparql http://my-sparql-endpoint...
+    
+    ... Your SPARQL query ...
+    ```
+    '''
     try:
         return query(cell, endpoint=line, print_table=True)
     except HTTPError as ex:
         error_message = ex.read().decode('utf-8')
         print('Error {}. Reason: {}'.format(ex.status, ex.reason))
-        print(error_message)
+        print(error_message, file=sys.stderr)
 
 
 def show_photos(values):