Refactor: Isolate column rendering from printing.

This change moves the core logic for rendering columns from the
columnize() method to a new helper method, render_columns().

Author: kmvanbrunt

cmd2/cmd2.py

@@ -4243,22 +4243,26 @@ def _print_documented_command_topics(self, header: str, cmds: list[str], verbose
         category_grid.add_row(topics_table)
         self.poutput(category_grid, "")
 
-    def columnize(self, str_list: list[str] | None, display_width: int = 80) -> None:
-        """Display a list of single-line strings as a compact set of columns.
+    def render_columns(self, str_list: list[str] | None, display_width: int = 80) -> str:
+        """Render a list of single-line strings as a compact set of columns.
 
-        Override of cmd's columnize() to handle strings with ANSI style sequences and wide characters.
+        This method correctly handles strings containing ANSI escape codes and
+        full-width characters (like those used in CJK languages). Each column is
+        only as wide as necessary and columns are separated by two spaces.
 
-        Each column is only as wide as necessary.
-        Columns are separated by two spaces (one was not legible enough).
+        :param str_list: list of single-line strings to display
+        :param display_width: max number of display columns to fit into
+        :return: a string containing the columnized output
         """
         if not str_list:
-            self.poutput("<empty>")
-            return
+            return ""
 
         size = len(str_list)
         if size == 1:
-            self.poutput(str_list[0])
-            return
+            return str_list[0]
+
+        rows: list[str] = []
+
         # Try every row count from 1 upwards
         for nrows in range(1, len(str_list)):
             ncols = (size + nrows - 1) // nrows
@@ -4294,7 +4298,22 @@ def columnize(self, str_list: list[str] | None, display_width: int = 80) -> None
                 del texts[-1]
             for col in range(len(texts)):
                 texts[col] = su.align_left(texts[col], width=colwidths[col])
-            self.poutput("  ".join(texts))
+            rows.append("  ".join(texts))
+
+        return "\n".join(rows)
+
+    def columnize(self, str_list: list[str] | None, display_width: int = 80) -> None:
+        """Display a list of single-line strings as a compact set of columns.
+
+        Override of cmd's columnize() that uses the render_columns() method.
+        The method correctly handles strings with ANSI style sequences and
+        full-width characters (like those used in CJK languages).
+
+        :param str_list: list of single-line strings to display
+        :param display_width: max number of display columns to fit into
+        """
+        columnized_strs = self.render_columns(str_list, display_width)
+        self.poutput(columnized_strs)
 
     @staticmethod
     def _build_shortcuts_parser() -> Cmd2ArgumentParser:

cmd2/string_utils.py

@@ -1,9 +1,8 @@
 """Provides string utility functions.
 
 This module offers a collection of string utility functions built on the Rich library.
-These utilities are designed to correctly handle strings with complex formatting, such as
-ANSI escape codes and full-width characters (like those used in CJK languages), which the
-standard Python library's string methods do not properly support.
+These utilities are designed to correctly handle strings with ANSI escape codes and
+full-width characters (like those used in CJK languages).
 """
 
 from rich.align import AlignMethod
@@ -107,7 +106,7 @@ def strip_style(val: str) -> str:
 def str_width(val: str) -> int:
     """Return the display width of a string.
 
-    This is intended for single line strings.
+    This is intended for single-line strings.
     Replace tabs with spaces before calling this.
 
     :param val: the string being measured

tests/test_cmd2.py

@@ -1355,22 +1355,35 @@ def test_help_verbose_with_fake_command(capsys) -> None:
     assert cmds[1] not in out
 
 
-def test_columnize_empty_list(capsys) -> None:
-    help_app = HelpApp()
+def test_render_columns_no_strs(help_app: HelpApp) -> None:
     no_strs = []
-    help_app.columnize(no_strs)
-    out, err = capsys.readouterr()
-    assert "<empty>" in out
+    result = help_app.render_columns(no_strs)
+    assert result == ""
 
 
-def test_columnize_too_wide(capsys) -> None:
-    help_app = HelpApp()
+def test_render_columns_one_str(help_app: HelpApp) -> None:
+    one_str = ["one_string"]
+    result = help_app.render_columns(one_str)
+    assert result == "one_string"
+
+
+def test_render_columns_too_wide(help_app: HelpApp) -> None:
     commands = ["kind_of_long_string", "a_slightly_longer_string"]
-    help_app.columnize(commands, display_width=10)
+    result = help_app.render_columns(commands, display_width=10)
+
+    expected = "kind_of_long_string     \na_slightly_longer_string"
+    assert result == expected
+
+
+def test_columnize(capsys: pytest.CaptureFixture[str]) -> None:
+    help_app = HelpApp()
+    items = ["one", "two"]
+    help_app.columnize(items)
     out, err = capsys.readouterr()
 
-    expected = "kind_of_long_string     \na_slightly_longer_string\n"
-    assert expected == out
+    # poutput() adds a newline at the end.
+    expected = "one  two\n"
+    assert out == expected
 
 
 class HelpCategoriesApp(cmd2.Cmd):