Allow the fill character to be colon by looking for expected directiv…

…es in each split

src/ansi_string/ansi_string.py

@@ -33,7 +33,7 @@
 )
 from .ansi_parsing import ParsedAnsiControlSequenceString, parse_graphic_sequence, settings_to_dict
 
-__version__ = '1.1.8'
+__version__ = '1.1.9'
 PACKAGE_NAME = 'ansi_string'
 
 # Constant: all characters considered to be whitespaces - this is used in strip functionality
@@ -748,7 +748,23 @@ def to_str(self, __format_spec:str=None, optimize:bool=True, reset_start:bool=Fa
             # Make a copy
             obj = self.copy()
 
-            format_parts = __format_spec.split(':', 1)
+            format_parts = __format_spec.split(':', 2)
+
+            # If more than 2 colons found, its meaning can be determined by ansi_format spec - if it starts with [
+            if len(format_parts) > 2:
+                if format_parts[1].endswith('['):
+                    # Third colon needs to be within ansi_format
+                    format_parts[1] = ':'.join(format_parts[1:])
+                else:
+                    # Second colon should be treated as fill character for string_format
+                    format_parts[0] = ':'.join(format_parts[0:2])
+                    format_parts[1] = format_parts[2]
+                del format_parts[2]
+            # Allow for fill char to be colon when no ansi_format is specified by looking for justification char which
+            # shouldn't exist in ansi_format spec unless it starts with [
+            elif len(format_parts) > 1 and re.match(r'^[-\+]?[<>\^]', format_parts[1]) is not None:
+                format_parts[0] = ':'.join(format_parts[0:])
+                del format_parts[1]
 
             if len(format_parts) > 1:
                 # ANSI color/style formatting

tests/test_ansi_string.py

@@ -187,6 +187,34 @@ def test_format_right_only(self):
             '###############################################################This has no ANSI formatting'
         )
 
+    def test_format_colon_fillchar(self):
+        s = AnsiString('This has no ANSI formatting')
+        self.assertEqual(
+            f'{s::>90}',
+            ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::This has no ANSI formatting'
+        )
+
+    def test_format_colon_fillchar2(self):
+        s = AnsiString('This has no ANSI formatting')
+        self.assertEqual(
+            f'{s::->90}',
+            ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::This has no ANSI formatting'
+        )
+
+    def test_format_colon_fillchar3(self):
+        s = AnsiString('This has no ANSI formatting')
+        self.assertEqual(
+            f'{s::>90:}',
+            ':::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::This has no ANSI formatting'
+        )
+
+    def test_format_colon_in_ansi_settings(self):
+        s = AnsiString('ANSI string')
+        self.assertEqual(
+            f'{s::[:}',
+            '\x1b[:mANSI string\x1b[m'
+        )
+
     def test_format_right_justify_and_int(self):
         s = AnsiString('This string will be formatted bold and red, right justify')
         self.assertEqual(