Small perf optimization for `expr | ""` mapping to `Optional(expr)`

1 files changed, 3 insertions, 0 deletions

diff --git a/pyparsing/core.py b/pyparsing/core.py
index ae7dcb6..03371ab 100644
--- a/pyparsing/core.py
+++ b/pyparsing/core.py
@@ -1552,6 +1552,9 @@ class ParserElement(ABC):
             return _PendingSkip(self, must_skip=True)
 
         if isinstance(other, str_type):
+            # `expr | ""` is equivalent to `Opt(expr)`
+            if other == "":
+                return Opt(self)
             other = self._literalStringClass(other)
         if not isinstance(other, ParserElement):
             return NotImplemented