Merge branch 'jannschu/master'

Fixes #95.

pybtex/database/input/bibtex.py

@@ -77,7 +77,7 @@ import six
 
 from pybtex import textutils
 from pybtex.bibtex.utils import split_name_list
-from pybtex.database import Entry, Person
+from pybtex.database import Entry, Person, BibliographyDataError
 from pybtex.database.input import BaseParser
 from pybtex.scanner import (
     Literal, Pattern, PrematureEOF, PybtexSyntaxError, Scanner
@@ -111,6 +111,10 @@ class UndefinedMacro(PybtexSyntaxError):
     error_type = 'undefined string'
 
 
+class DuplicatePersonField(BibliographyDataError):
+    pass
+
+
 class LowLevelParser(Scanner):
     NAME = Pattern(r'[{0}][{1}]*'.format(re.escape(NAME_CHARS), re.escape(NAME_CHARS + digits)), 'a valid name')
     KEY_PAREN = Pattern(r'[^\s\,]+', 'entry key')
@@ -350,11 +354,19 @@ class Parser(BaseParser):
             key = 'unnamed-%i' % self.unnamed_entry_counter
             self.unnamed_entry_counter += 1
 
+        already_handled_person_fields = set()
         for field_name, field_value_list in fields:
             field_value = textutils.normalize_whitespace(self.flatten_value_list(field_value_list))
             if field_name in self.person_fields:
+                if field_name in already_handled_person_fields:
+                    error_message = 'entry with key {} has a duplicate {} field'.format(
+                        key, field_name
+                    )
+                    self.handle_error(DuplicatePersonField(error_message))
+                    continue
                 for name in split_name_list(field_value):
                     entry.add_person(Person(name), field_name)
+                already_handled_person_fields.add(field_name)
             else:
                 entry.fields[field_name] = field_value
         self.data.add_entry(key, entry)