fix: handle negative imaginary parts in number_to_string

CHANGELOG.md

@@ -1,5 +1,8 @@
 # DeepDiff Change log
 
+- Unreleased
+    - Fixed `number_to_string` raising `ValueError` for complex numbers with a negative imaginary part
+
 - v9-1-0
     - Added multiprocessing support for DeepDiff: parallel distance computation and parallel subtree diffing with aggregated worker stats, deterministic ordering, and automatic fallback to serial when unsafe (e.g. `custom_operators`, `*_obj_callback`, `ignore_order_func`)
     - Added wildcard/glob pattern support for `exclude_paths` and `include_paths` thanks to [akshat62](https://github.com/akshat62)

deepdiff/helper.py

@@ -496,19 +496,21 @@ def number_to_string(number: Any, significant_digits: int, number_format_notatio
             number = int(number)
     elif isinstance(number, only_complex_number):  # type: ignore
         # Case for complex numbers.
+        real = number_to_string(
+            number=number.real,  # type: ignore
+            significant_digits=significant_digits,
+            number_format_notation=number_format_notation
+        )
+        imag = number_to_string(
+            number=number.imag,  # type: ignore
+            significant_digits=significant_digits,
+            number_format_notation=number_format_notation
+        )
+        # A negative imaginary part already carries its own sign. Adding another
+        # one produces a malformed string such as "1.0+-1.0j" that complex() rejects.
+        sign = '' if str(imag).startswith('-') else '+'
         number = number.__class__(
-            "{real}+{imag}j".format(  # type: ignore
-                real=number_to_string(
-                    number=number.real,  # type: ignore
-                    significant_digits=significant_digits,
-                    number_format_notation=number_format_notation
-                ),
-                imag=number_to_string(
-                    number=number.imag,  # type: ignore
-                    significant_digits=significant_digits,
-                    number_format_notation=number_format_notation
-                )
-            )  # type: ignore
+            "{real}{sign}{imag}j".format(real=real, sign=sign, imag=imag)  # type: ignore
         )
     else:
         number = round(number=number, ndigits=significant_digits)  # type: ignore

tests/test_helper.py

@@ -184,6 +184,10 @@ def test_number_to_string_decimal_digits(self, t1, t2, significant_digits, numbe
                                  (-0j, 0.2j, 5, "e", ('0.00000e+0', '0.00000e+0+2.00000e-1j')),
                                  (-0j, 0.2j, 0, "f", True),
                                  (-0j, 0.2j, 0, "e", True),
+                                 (1-1j, 1-1j, 1, "f", True),
+                                 (1-1j, 1.2-1.2j, 1, "f", ('1.0-1.0j', '1.2-1.2j')),
+                                 (1-1j, 1.2-1.2j, 1, "e", ('1.0e+0-1.0e+0j', '1.2e+0-1.2e+0j')),
+                                 (-1-1j, -1.2-1.2j, 1, "f", ('-1.0-1.0j', '-1.2-1.2j')),
                              ])
     def test_number_to_string_complex_digits(self, t1, t2, significant_digits, number_format_notation, expected_result):
         st1 = number_to_string(t1, significant_digits=significant_digits, number_format_notation=number_format_notation)