Add support for conditional text to template mini-language

src/calibre/ebooks/metadata/book/base.py

@@ -17,7 +17,6 @@ from calibre.library.field_metadata import FieldMetadata
 from calibre.utils.date import isoformat, format_date
 
 
-
 NULL_VALUES = {
                 'user_metadata': {},
                 'cover_data'   : (None, None),
@@ -38,10 +37,17 @@ class SafeFormat(string.Formatter):
     Provides a format function that substitutes '' for any missing value
     '''
     def get_value(self, key, args, mi):
-        ign, v = mi.format_field(key, series_with_index=False)
-        if v is None:
-            return ''
-        return v
+        from calibre.library.save_to_disk import explode_string_template_value
+        try:
+            prefix, key, suffix = explode_string_template_value(key)
+            ign, v = mi.format_field(key, series_with_index=False)
+            if v is None:
+                return ''
+            if v is '':
+                return ''
+            return prefix + v + suffix
+        except:
+            return key
 
 composite_formatter = SafeFormat()
 compress_spaces = re.compile(r'\s+')
@@ -50,6 +56,7 @@ def format_composite(x, mi):
     try:
         ans = composite_formatter.vformat(x, [], mi).strip()
     except:
+        traceback.print_exc()
         ans = x
     return compress_spaces.sub(' ', ans)
 

src/calibre/gui2/dialogs/metadata_bulk.py

@@ -122,15 +122,6 @@ class SafeFormat(string.Formatter):
             v = ','.join(v)
         return v
 
-composite_formatter = SafeFormat()
-
-def format_composite(x, mi):
-    try:
-        ans = composite_formatter.vformat(x, [], mi).strip()
-    except:
-        ans = x
-    return ans
-
 class MetadataBulkDialog(QDialog, Ui_MetadataBulkDialog):
 
     s_r_functions = {       ''              : lambda x: x,

src/calibre/library/save_to_disk.py

@@ -101,15 +101,30 @@ def preprocess_template(template):
         template = template.decode(preferred_encoding, 'replace')
     return template
 
+template_value_re = re.compile(r'^([^\|]*(?=\|))(?:\|?)([^\|]*)(?:\|?)((?<=\|).*?)$')
+
+def explode_string_template_value(key):
+    try:
+        matches = template_value_re.match(key)
+        if matches.lastindex != 3:
+            return key
+        return matches.groups()
+    except:
+        return '', key, ''
+
 class SafeFormat(string.Formatter):
     '''
     Provides a format function that substitutes '' for any missing value
     '''
     def get_value(self, key, args, kwargs):
         try:
-            return kwargs[key]
+            prefix, key, suffix = explode_string_template_value(key)
+            if kwargs[key]:
+                return '%s%s%s'%(prefix, kwargs[key], suffix)
+            return ''
         except:
             return ''
+
 safe_formatter = SafeFormat()
 
 def safe_format(x, format_args):