atol bug-fix for leading underscores

- Support leading underscores (bug fix) for prefixed literal
- Added relevant tests
- Updated docstring for clarity

Signed-off-by: Joshua James Venter <[email protected]>

docs/changelog.md

@@ -399,6 +399,10 @@ what we publish.
 - `LegacyPointer.load/store` are now removed. It's use is replaced with
   `__getitem__` or `__setitem__`.
 
+- The `atol` function now correctly supports leading underscores,
+  (e.g.`atol("0x_ff", 0)`), for non-base-10 integer literals as per Python's
+  [Integer Literals](https://docs.python.org/3/reference/lexical_analysis.html#integers).
+
 ### ❌ Removed
 
 - It is no longer possible to cast (implicitly or explicitly) from `Reference`

stdlib/src/builtin/string.mojo

@@ -287,17 +287,17 @@ fn _atol(str_ref: StringRef, base: Int = 10) raises -> Int:
     # single underscores are only allowed between digits
     # starting "was_last_digit_undescore" to true such that
     # if the first digit is an undesrcore an error is raised
-    var was_last_digit_undescore = True
+    var was_last_digit_underscore = real_base == 10
     for pos in range(start, str_len):
         var ord_current = int(buff[pos])
         if ord_current == ord_underscore:
-            if was_last_digit_undescore:
+            if was_last_digit_underscore:
                 raise Error(_atol_error(base, str_ref))
             else:
-                was_last_digit_undescore = True
+                was_last_digit_underscore = True
                 continue
         else:
-            was_last_digit_undescore = False
+            was_last_digit_underscore = False
         if ord_0 <= ord_current <= ord_num_max:
             result += ord_current - ord_0
             found_valid_chars_after_start = True
@@ -322,7 +322,7 @@ fn _atol(str_ref: StringRef, base: Int = 10) raises -> Int:
                 )
             result = nextresult
 
-    if was_last_digit_undescore or (not found_valid_chars_after_start):
+    if was_last_digit_underscore or (not found_valid_chars_after_start):
         raise Error(_atol_error(base, str_ref))
 
     if has_space_after_number:
@@ -381,20 +381,37 @@ fn _identify_base(str_ref: StringRef, start: Int) -> Tuple[Int, Int]:
 fn atol(str: String, base: Int = 10) raises -> Int:
     """Parses and returns the given string as an integer in the given base.
 
-    For example, `atol("19")` returns `19`. If base is 0 the the string is
-    parsed as an Integer literal, see: https://docs.python.org/3/reference/lexical_analysis.html#integers.
-
-    Raises:
-        If the given string cannot be parsed as an integer value. For example in
-        `atol("hi")`.
+    If base is set to 0, the string is parsed as an Integer literal, with the
+    following considerations:
+    - '0b' or '0B' prefix indicates binary (base 2)
+    - '0o' or '0O' prefix indicates octal (base 8)
+    - '0x' or '0X' prefix indicates hexadecimal (base 16)
+    - Without a prefix, it's treated as decimal (base 10)
 
     Args:
         str: A string to be parsed as an integer in the given base.
         base: Base used for conversion, value must be between 2 and 36, or 0.
 
     Returns:
-        An integer value that represents the string, or otherwise raises.
-    """
+        An integer value that represents the string.
+
+    Raises:
+        If the given string cannot be parsed as an integer value or if an
+        incorrect base is provided.
+
+    Examples:
+        >>> atol("32")
+        32
+        >>> atol("FF", 16)
+        255
+        >>> atol("0xFF", 0)
+        255
+        >>> atol("0b1010", 0)
+        10
+
+    Notes:
+        This follows [Python's integer literals](
+        https://docs.python.org/3/reference/lexical_analysis.html#integers)."""
     return _atol(str._strref_dangerous(), base)
 
 

stdlib/test/builtin/test_string.mojo

@@ -365,6 +365,9 @@ def test_atol():
     assert_equal(10, atol("0o12", 8))
     assert_equal(10, atol("0O12", 8))
     assert_equal(35, atol("Z", 36))
+    assert_equal(255, atol("0x_00_ff", 16))
+    assert_equal(18, atol("0b0001_0010", 2))
+    assert_equal(18, atol("0b_000_1001_0", 2))
 
     # Negative cases
     with assert_raises(
@@ -433,6 +436,14 @@ def test_atol_base_0():
 
     assert_equal(0, atol("0X0", base=0))
 
+    assert_equal(255, atol("0x_00_ff", base=0))
+
+    assert_equal(18, atol("0b_0001_0010", base=0))
+    assert_equal(18, atol("0b000_1001_0", base=0))
+
+    assert_equal(10, atol("0o_000_12", base=0))
+    assert_equal(10, atol("0o00_12", base=0))
+
     with assert_raises(
         contains="String is not convertible to integer with base 0: '  0x'"
     ):
@@ -453,11 +464,6 @@ def test_atol_base_0():
     ):
         _ = atol("0r100", base=0)
 
-    with assert_raises(
-        contains="String is not convertible to integer with base 0: '0b_0'"
-    ):
-        _ = atol("0b_0", base=0)
-
     with assert_raises(
         contains="String is not convertible to integer with base 0: '0xf__f'"
     ):