From 6c89e09169825a805575561f1e36bb2063149721 Mon Sep 17 00:00:00 2001
From: andrewgsavage <andrewgsavage@gmail.com>
Date: Tue, 11 Jun 2024 20:36:20 +0100
Subject: [PATCH] format

---
 pint/delegates/formatter/_format_helpers.py | 5 ++++-
 pint/delegates/formatter/full.py            | 6 +++++-
 pint/delegates/formatter/plain.py           | 9 +++++++++
 3 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/pint/delegates/formatter/_format_helpers.py b/pint/delegates/formatter/_format_helpers.py
index 995159e65..501c72c7a 100644
--- a/pint/delegates/formatter/_format_helpers.py
+++ b/pint/delegates/formatter/_format_helpers.py
@@ -161,6 +161,7 @@ def formatter(
     power_fmt: str = "{} ** {}",
     parentheses_fmt: str = "({0})",
     exp_call: FORMATTER = "{:n}".format,
+    empty_numerator_fmt = "1",
 ) -> str:
     """Format a list of (name, exponent) pairs.
 
@@ -183,6 +184,8 @@ def formatter(
         the format used for parenthesis. (Default value = "({0})")
     exp_call : callable
          (Default value = lambda x: f"{x:n}")
+    empty_numerator_fmt : str
+        the format used for an empty numerator. (Default value = "1")
 
     Returns
     -------
@@ -218,7 +221,7 @@ def formatter(
         return join_u(product_fmt, pos_terms + neg_terms)
 
     # Show as Ratio: positive terms / negative terms
-    pos_ret = join_u(product_fmt, pos_terms) or "1"
+    pos_ret = join_u(product_fmt, pos_terms) or empty_numerator_fmt
 
     if not neg_terms:
         return pos_ret
diff --git a/pint/delegates/formatter/full.py b/pint/delegates/formatter/full.py
index 92609b713..c3bf49ef4 100644
--- a/pint/delegates/formatter/full.py
+++ b/pint/delegates/formatter/full.py
@@ -131,10 +131,14 @@ def format_unit(
     ) -> str:
         uspec = uspec or self.default_format
         sort_func = sort_func or self.default_sort_func
+        empty_numerator_fmt = "1"
         if isinstance(unit._units, NonReducingUnitsContainer):
             sort_func = _sort_func
+            empty_numerator_fmt = ""
         return self.get_formatter(uspec).format_unit(
-            unit, uspec, sort_func=sort_func, **babel_kwds
+            unit, uspec, sort_func=sort_func, 
+                        empty_numerator_fmt = empty_numerator_fmt,
+**babel_kwds
         )
 
     def format_quantity(
diff --git a/pint/delegates/formatter/plain.py b/pint/delegates/formatter/plain.py
index d40ec1ae0..d03c00959 100644
--- a/pint/delegates/formatter/plain.py
+++ b/pint/delegates/formatter/plain.py
@@ -81,6 +81,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+        empty_numerator_fmt = "1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         """Format a unit (can be compound) into string
@@ -203,6 +204,7 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+        empty_numerator_fmt = "1",
         **babel_kwds: Unpack[BabelKwds],
     ) -> str:
         numerator, denominator = prepare_compount_unit(
@@ -225,6 +227,7 @@ def format_unit(
             division_fmt=division_fmt,
             power_fmt="{}**{}",
             parentheses_fmt=r"({})",
+            empty_numerator_fmt=empty_numerator_fmt,
         )
 
     def format_quantity(
@@ -313,12 +316,16 @@ def format_unit(
         unit: PlainUnit | Iterable[tuple[str, Any]],
         uspec: str = "",
         sort_func: SortFunc | None = None,
+                                        empty_numerator_fmt="1",
+
         **babel_kwds: Unpack[BabelKwds],
+
     ) -> str:
         numerator, denominator = prepare_compount_unit(
             unit,
             uspec,
             sort_func=sort_func,
+
             **babel_kwds,
             registry=self._registry,
         )
@@ -339,6 +346,8 @@ def format_unit(
             power_fmt="{}{}",
             parentheses_fmt="({})",
             exp_call=pretty_fmt_exponent,
+                        empty_numerator_fmt=empty_numerator_fmt,
+
         )
 
     def format_quantity(