Backport PR #38759: BUG: float-like string, trailing 0 truncation (#38769)

Co-authored-by: mzeitlin11 <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v1.2.1.rst

@@ -16,6 +16,7 @@ Fixed regressions
 ~~~~~~~~~~~~~~~~~
 - The deprecated attributes ``_AXIS_NAMES`` and ``_AXIS_NUMBERS`` of :class:`DataFrame` and :class:`Series` will no longer show up in ``dir`` or ``inspect.getmembers`` calls (:issue:`38740`)
 - :meth:`to_csv` created corrupted zip files when there were more rows than ``chunksize`` (issue:`38714`)
+- Bug in repr of float-like strings of an ``object`` dtype having trailing 0's truncated after the decimal (:issue:`38708`)
 -
 
 .. ---------------------------------------------------------------------------

pandas/io/formats/format.py

@@ -1305,7 +1305,7 @@ def _format(x):
             if not is_float_type[i] and leading_space:
                 fmt_values.append(f" {_format(v)}")
             elif is_float_type[i]:
-                fmt_values.append(float_format(v))
+                fmt_values.append(_trim_zeros_single_float(float_format(v)))
             else:
                 if leading_space is False:
                     # False specifically, so that the default is
@@ -1315,8 +1315,6 @@ def _format(x):
                     tpl = " {v}"
                 fmt_values.append(tpl.format(v=_format(v)))
 
-        fmt_values = _trim_zeros_float(str_floats=fmt_values, decimal=".")
-
         return fmt_values
 
 
@@ -1832,11 +1830,25 @@ def _trim_zeros_complex(str_complexes: np.ndarray, decimal: str = ".") -> List[s
     return padded
 
 
+def _trim_zeros_single_float(str_float: str) -> str:
+    """
+    Trims trailing zeros after a decimal point,
+    leaving just one if necessary.
+    """
+    str_float = str_float.rstrip("0")
+    if str_float.endswith("."):
+        str_float += "0"
+
+    return str_float
+
+
 def _trim_zeros_float(
     str_floats: Union[np.ndarray, List[str]], decimal: str = "."
 ) -> List[str]:
     """
-    Trims zeros, leaving just one before the decimal points if need be.
+    Trims the maximum number of trailing zeros equally from
+    all numbers containing decimals, leaving just one if
+    necessary.
     """
     trimmed = str_floats
     number_regex = re.compile(fr"^\s*[\+-]?[0-9]+\{decimal}[0-9]*$")

pandas/tests/io/formats/test_format.py

@@ -2002,6 +2002,25 @@ def test_float_trim_zeros(self):
                 assert ("+10" in line) or skip
             skip = False
 
+    @pytest.mark.parametrize(
+        "data, expected",
+        [
+            (["3.50"], "0    3.50\ndtype: object"),
+            ([1.20, "1.00"], "0     1.2\n1    1.00\ndtype: object"),
+            ([np.nan], "0   NaN\ndtype: float64"),
+            ([None], "0    None\ndtype: object"),
+            (["3.50", np.nan], "0    3.50\n1     NaN\ndtype: object"),
+            ([3.50, np.nan], "0    3.5\n1    NaN\ndtype: float64"),
+            ([3.50, np.nan, "3.50"], "0     3.5\n1     NaN\n2    3.50\ndtype: object"),
+            ([3.50, None, "3.50"], "0     3.5\n1    None\n2    3.50\ndtype: object"),
+        ],
+    )
+    def test_repr_str_float_truncation(self, data, expected):
+        # GH#38708
+        series = Series(data)
+        result = repr(series)
+        assert result == expected
+
     def test_dict_entries(self):
         df = DataFrame({"A": [{"a": 1, "b": 2}]})