From 4e6ed110fd65b1b6c97cf4c18d59e958d22e4c02 Mon Sep 17 00:00:00 2001
From: cpascual <cpascual@cells.es>
Date: Mon, 23 Nov 2015 08:41:12 +0100
Subject: [PATCH] Use empty string for dimensionless abbreviated format

Make pint use empty string when formatting dimensionless units
(instead of "dimensionless") if the abbreviation format spec ("~")
is used.

See https://github.com/hgrecco/pint/issues/300
---
 pint/unit.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/pint/unit.py b/pint/unit.py
index 1aa7323..bbf9dfb 100644
--- a/pint/unit.py
+++ b/pint/unit.py
@@ -101,6 +101,8 @@ class _Unit(SharedRegistryObject):
         spec = spec or self.default_format
 
         if '~' in spec:
+            if self.dimensionless:
+                return ''
             units = UnitsContainer(dict((self._REGISTRY._get_symbol(key),
                                          value)
                                    for key, value in self._units.items()))