fix percentage handling (#1094)

* fix percentage handling

* add test

* fix lint errors

Co-authored-by: Samuel Sieb <samuel@sieb.net>

esphome/config_validation.py

@@ -838,9 +838,16 @@ def percentage(value):
 
 
 def possibly_negative_percentage(value):
-    has_percent_sign = isinstance(value, str) and value.endswith('%')
-    if has_percent_sign:
+    has_percent_sign = False
+    if isinstance(value, str):
+        try:
+            if value.endswith('%'):
+                has_percent_sign = False
                 value = float(value[:-1].rstrip()) / 100.0
+            else:
+                value = float(value)
+        except ValueError:
+            raise Invalid("invalid number")
     if value > 1:
         msg = "Percentage must not be higher than 100%."
         if not has_percent_sign:

tests/test3.yaml

@@ -14,6 +14,8 @@ esphome:
 substitutions:
   devicename: test3
   devicecomment: test3 device
+  min_sub: "0.03"
+  max_sub: "12.0%"
 
 api:
   port: 8000
@@ -769,6 +771,8 @@ servo:
   id: my_servo
   output: out
   restore: true
+  min_level: $min_sub
+  max_level: $max_sub
 
 ttp229_lsf: