Add a python script for checking that the examples match the event

schema.

Does the same checks as check.sh, but is a *lot* faster making it
suitable for using as a pre-commit hook.

I don't suggest replacing check.sh since it's good to check that the
schema works with multiple implementations of jsonschema.

event-schemas/check_examples.py

@@ -0,0 +1,62 @@
+#! /usr/bin/env python
+
+import sys
+import json
+import os
+
+
+def import_error(module, package, debian, error):
+    sys.stderr.write((
+        "Error importing %(module)s: %(error)r\n"
+        "To install %(module)s run:\n"
+        "  pip install %(package)s\n"
+        "or on Debian run:\n"
+        "  sudo apt-get install python-%(debian)s\n"
+    ) % locals())
+    if __name__ == '__main__':
+        sys.exit(1)
+
+try:
+    import jsonschema
+except ImportError as e:
+    import_error("jsonschema", "jsonschema", "jsonschema", e)
+    raise
+
+try:
+    import yaml
+except ImportError as e:
+    import_error("yaml", "PyYAML", "yaml", e)
+    raise
+
+
+def check_example_file(examplepath, schemapath):
+    with open(examplepath) as f:
+        example = yaml.load(f)
+
+    with open(schemapath) as f:
+        schema = yaml.load(f)
+
+    fileurl = "file://" + os.path.abspath(schemapath)
+
+    print ("Checking schema for: %r %r" % (examplepath, schemapath))
+    # Setting the 'id' tells jsonschema where the file is so that it
+    # can correctly resolve relative $ref references in the schema
+    schema['id'] = fileurl
+    try:
+        jsonschema.validate(example, schema)
+    except:
+        raise ValueError("Error validating JSON schema for %r %r" % (
+            examplepath, schemapath
+        ), e)
+
+
+def check_example_dir(exampledir, schemadir):
+    for root, dirs, files in os.walk(exampledir):
+        for filename in files:
+            examplepath = os.path.join(root, filename)
+            schemapath = examplepath.replace(exampledir, schemadir)
+            check_example_file(examplepath, schemapath)
+
+
+if __name__ == '__main__':
+    check_example_dir("examples", "schema")