bugfix our center() padding algorithm

jquast · jquast · commit d622de15f478 · 2026-01-24T19:52:09.000-05:00
diff --git a/docs/intro.rst b/docs/intro.rst
@@ -442,6 +442,9 @@ languages.
 History
 =======
 
+*next version*
+  * **Bugfix** our `center()`_ to better match padding of `str.center()`_.
+
 0.3.3 *2026-01-24*
   * **Performance** improvement in `width()`_. `PR #185`_.
   * **Bugfix** missing ``py.typed``, ``Typing :: Typed``. `PR #184`_.
diff --git a/tests/test_justify.py b/tests/test_justify.py
@@ -10,13 +10,15 @@
 
 
 def test_ljust():
-    assert ljust('hi', 5) == 'hi   '
-    assert ljust('', 5) == '     '
-    assert ljust('hello', 3) == 'hello'
-    assert ljust('hello', 5) == 'hello'
+    # our ljust() matches standard python ljust() for ascii
+    assert ljust('hi', 5) == 'hi   ' == str.ljust('hi', 5)
+    assert ljust('', 5) == '     ' == str.ljust('', 5)
+    assert ljust('hello', 3) == 'hello' == str.ljust('hello', 3)
+    assert ljust('hello', 5) == 'hello' == str.ljust('hello', 5)
+    assert ljust('hi', 5, fillchar='-') == 'hi---' == str.ljust('hi', 5, '-')
+    # advanced capabilities
     assert ljust('\x1b[31mhi\x1b[0m', 5) == '\x1b[31mhi\x1b[0m   '
     assert ljust('\u4e2d', 4) == '\u4e2d  '
-    assert ljust('hi', 5, fillchar='-') == 'hi---'
     assert ljust('hi', 5, fillchar='\u00b7') == 'hi\u00b7\u00b7\u00b7'
     assert ljust(CJK_WORD, 8) == CJK_WORD + '    '
     assert width(ljust(CJK_WORD, 8)) == 8
@@ -27,30 +29,35 @@ def test_ljust():
 
 
 def test_rjust():
-    assert rjust('hi', 5) == '   hi'
-    assert rjust('', 5) == '     '
-    assert rjust('hello', 3) == 'hello'
-    assert rjust('hello', 5) == 'hello'
+    # our rjust() matches standard python rjust() for ascii
+    assert rjust('hi', 5) == '   hi' == str.rjust('hi', 5)
+    assert rjust('', 5) == '     ' == str.rjust('', 5)
+    assert rjust('hello', 3) == 'hello' == str.rjust('hello', 3)
+    assert rjust('hello', 5) == 'hello' == str.rjust('hello', 5)
+    assert rjust('hi', 5, fillchar='-') == '---hi' == str.rjust('hi', 5, '-')
+    # advanced capabilities
     assert rjust('\x1b[31mhi\x1b[0m', 5) == '   \x1b[31mhi\x1b[0m'
     assert rjust('\u4e2d', 4) == '  \u4e2d'
-    assert rjust('hi', 5, fillchar='-') == '---hi'
     assert rjust('hi', 5, fillchar='\u00b7') == '\u00b7\u00b7\u00b7hi'
     assert rjust(CJK_WORD, 8) == '    ' + CJK_WORD
     assert width(rjust(CAFE_COMBINING, 8)) == 8
     assert width(rjust(EMOJI_FAMILY, 6)) == 6
 
 
 def test_center():
-    assert center('hi', 6) == '  hi  '
-    assert center('hi', 5) == ' hi  '
-    assert center('', 4) == '    '
-    assert center('hello', 3) == 'hello'
-    assert center('hello', 5) == 'hello'
+    # our center() matches standard python center() for ascii
+    assert center('hi', 6) == '  hi  ' == str.center('hi', 6)
+    assert center('hi', 5) == '  hi ' == str.center('hi', 5)
+    assert center('ab', 7) == '   ab  ' == str.center('ab', 7)
+    assert center('', 4) == '    ' == str.center('', 4)
+    assert center('hello', 3) == 'hello' == str.center('hello', 3)
+    assert center('hello', 5) == 'hello' == str.center('hello', 5)
+    assert center('hi', 6, fillchar='-') == '--hi--' == str.center('hi', 6, '-')
+    assert center('x', 4) == ' x  ' == str.center('x', 4)
+    # advanced capabilities
     assert center('\x1b[31mhi\x1b[0m', 6) == '  \x1b[31mhi\x1b[0m  '
     assert center('\u4e2d', 6) == '  \u4e2d  '
-    assert center('hi', 6, fillchar='-') == '--hi--'
     assert center('hi', 6, fillchar='\u00b7') == '\u00b7\u00b7hi\u00b7\u00b7'
-    assert center('x', 4) == ' x  '
     assert width(center(CJK_WORD, 8)) == 8
     assert width(center(CAFE_COMBINING, 8)) == 8
     assert width(center(EMOJI_FAMILY, 6)) == 6
diff --git a/wcwidth/wcwidth.py b/wcwidth/wcwidth.py
@@ -742,7 +742,8 @@ def center(
     else:
         text_width = width(text, control_codes=control_codes, ambiguous_width=ambiguous_width)
     total_padding = max(0, dest_width - text_width)
-    left_pad = total_padding // 2
+    # matching https://jazcap53.github.io/pythons-eccentric-strcenter.html
+    left_pad = total_padding // 2 + (total_padding & dest_width & 1)
     right_pad = total_padding - left_pad
     return fillchar * left_pad + text + fillchar * right_pad
 
