Panic if a Duration string has multiple minus signs (#4358)

polars/polars-time/src/windows/duration.rs

@@ -56,6 +56,14 @@ impl Duration {
     ///
     /// # Panics if given str is incorrect
     pub fn parse(duration: &str) -> Self {
+        let num_minus_signs = duration.matches('-').count();
+        if num_minus_signs > 1 {
+            panic!("a Duration string can only have a single minus sign")
+        }
+        if (num_minus_signs > 0) & !duration.starts_with('-') {
+            panic!("only a single minus sign is allowed, at the front of the string")
+        }
+
         let mut nsecs = 0;
         let mut months = 0;
         let mut iter = duration.char_indices();

py-polars/polars/internals/expr.py

@@ -7042,8 +7042,9 @@ def offset_by(self, by: str) -> Expr:
         """
         Offset this date by a relative time offset.
 
-         This differs from `pl.col("foo") + timedelta` in that it can
-         take months and leap years into account
+        This differs from ``pl.col("foo") + timedelta`` in that it can
+        take months and leap years into account. Note that only a single minus
+        sign is allowed in the ``by`` string, as the first character.
 
         Parameters
         ----------

py-polars/polars/internals/series.py

@@ -5843,8 +5843,9 @@ def offset_by(self, by: str) -> Series:
         """
         Offset this date by a relative time offset.
 
-         This differs from `pl.col("foo") + timedelta` in that it can
-         take months and leap years into account
+        This differs from ``pl.col("foo") + timedelta`` in that it can
+        take months and leap years into account. Note that only a single minus
+        sign is allowed in the ``by`` string, as the first character.
 
         Parameters
         ----------