fix formatting of positive numbers with negative exponents (#590)

* correct the formatting for positive numbers with negative exponents and add additional test

* add case for negative exponent truncation, add guard for the mantissa

* delete unnecessary else statement

Author: adrianmolzon

bayes_opt/logger.py

@@ -82,7 +82,7 @@ def _format_number(self, x: float) -> str:
             result = ""
             width = self._default_cell_size
             # Keep negative sign, exponent, and as many decimal places as possible
-            if "-" in s:
+            if x < 0:
                 result += "-"
                 width -= 1
                 s = s[1:]
@@ -96,8 +96,6 @@ def _format_number(self, x: float) -> str:
                 width -= dot_pos
                 if width > 0:
                     result += s[dot_pos : dot_pos + width]
-            else:
-                result += s[:width]
             if "e" in s:
                 result += end
             result = result.ljust(self._default_cell_size)

tests/test_logger.py

@@ -87,7 +87,14 @@ def test_format_number():
     assert len(formatted) == logger._default_cell_size
     assert formatted == "1.234e+13"
 
-    # Test negative scientific notation truncation
+    sci_float = 1.11111111e-5
+    formatted = logger._format_number(sci_float)
+    assert formatted == "1.111e-05"
+
+    sci_float_neg = -1.11111111e-5
+    formatted = logger._format_number(sci_float_neg)
+    assert formatted == "-1.11e-05"
+
     sci_float = -12345678901234.5678901234
     formatted = logger._format_number(sci_float)
     assert len(formatted) == logger._default_cell_size