Adding error handling for YAML import.

1.  Moving all YAML library usage into 'util.py' via utility function.
2.  Wrapping 'import yaml' in error handling to report what library to install.

bin/lesson_check.py

@@ -8,7 +8,6 @@
 import os
 import glob
 import json
-import yaml
 import re
 from optparse import OptionParser
 
@@ -131,8 +130,7 @@ def check_config(reporter, source_dir):
     """Check configuration file."""
 
     config_file = os.path.join(source_dir, '_config.yml')
-    with open(config_file, 'r') as reader:
-        config = yaml.load(reader)
+    config = load_yaml(config_file)
     reporter.check_field(config_file, 'configuration', config, 'kind', 'lesson')
 
 

bin/util.py

@@ -1,8 +1,12 @@
 import sys
 import json
-import yaml
 from subprocess import Popen, PIPE
 
+try:
+    import yaml
+except ImportError:
+    print('Unable to import YAML module: please install PyYAML', file=sys.stderr)
+    sys.exit(1)
 
 class Reporter(object):
     """Collect and report errors."""
@@ -106,3 +110,13 @@ def split_metadata(path, text):
             sys.exit(1)
 
     return metadata_raw, metadata_yaml, text
+
+
+def load_yaml(filename):
+    """
+    Wrapper around YAML loading so that 'import yaml' and error
+    handling is only needed in one place.
+    """
+
+    with open(filename, 'r') as reader:
+        return yaml.load(reader)

bin/workshop_check.py

@@ -7,7 +7,6 @@
 import sys
 import os
 import re
-import yaml
 from datetime import date
 from util import Reporter, split_metadata
 
@@ -373,13 +372,19 @@ def check_config(reporter, filename):
     Check YAML configuration file.
     """
 
-    with open(filename, 'r') as reader:
-        config = yaml.load(reader)
+    config = load_yaml(filename)
 
-    reporter.check(config['kind'] == 'workshop',
+    kind = config.get('kind', None)
+    reporter.check(kind == 'workshop',
                    filename,
-                   'Not configured as a workshop: found "{0}" instead',
-                   config['kind'])
+                   'Missing or unknown kind of event: {0}',
+                   kind)
+
+    carpentry = config.get('carpentry', None)
+    reporter.check(carpentry in ('swc', 'dc'),
+                   filename,
+                   'Missing or unknown carpentry: {0}',
+                   carpentry)
 
 
 def main():