Preserve form feed blank lines

CHANGELOG.md

@@ -8,6 +8,8 @@ Find out more about isort's release policy [here](docs/major_releases/release_po
 
 ### Unreleased
 
+  - Preserve form feed characters when they appear on otherwise blank lines (#2562)
+
 ### 8.0.0 February 19 2026 
 
   - Removed `--old-finders` and `--magic-placement` flags and `old_finders` configuration option. The legacy finder logic that relied on environment introspection has been removed (#2445) @joao-faria-dev

isort/output.py

@@ -132,9 +132,9 @@ def sorted_imports(
 
     if output:
         imports_tail = output_at + len(output)
-        while [
-            character.strip() for character in formatted_output[imports_tail : imports_tail + 1]
-        ] == [""]:
+        while formatted_output[imports_tail : imports_tail + 1] and _is_removable_blank_line(
+            formatted_output[imports_tail]
+        ):
             formatted_output.pop(imports_tail)
 
         if config.lines_before_imports != -1:
@@ -191,6 +191,10 @@ def sorted_imports(
     return _output_as_string(formatted_output, parsed.line_separator)
 
 
+def _is_removable_blank_line(line: str) -> bool:
+    return "\f" not in line and line.strip() == ""
+
+
 # Ignore DeepSource cyclomatic complexity check for this function.
 # skipcq: PY-R1000
 def _build_import_group(

isort/parse.py

@@ -1,5 +1,6 @@
 """Defines parsing functions used by isort for parsing import definitions"""
 
+import re
 from collections import OrderedDict, defaultdict
 from functools import partial
 from itertools import chain
@@ -19,6 +20,8 @@
 from .exceptions import MissingSection
 from .settings import DEFAULT_CONFIG, Config
 
+NEWLINE_RE = re.compile(r"\r\n|\r|\n")
+
 if TYPE_CHECKING:
     CommentsAboveDict = TypedDict(
         "CommentsAboveDict", {"straight": dict[str, list[str]], "from": dict[str, list[str]]}
@@ -77,9 +80,7 @@ class ParsedContent(NamedTuple):
 def file_contents(contents: str, config: Config = DEFAULT_CONFIG) -> ParsedContent:
     """Parses a python file taking out and categorizing imports."""
     line_separator: str = config.line_ending or _infer_line_separator(contents)
-    in_lines = contents.splitlines()
-    if contents and contents[-1] in ("\n", "\r"):
-        in_lines.append("")
+    in_lines = NEWLINE_RE.split(contents) if contents else []
 
     out_lines = []
     original_line_count = len(in_lines)

tests/unit/test_regressions.py

@@ -99,6 +99,12 @@ def test_blank_lined_removed_issue_1283():
     assert isort.code(test_input) == test_input
 
 
+def test_form_feed_blank_line_not_removed_issue_2562():
+    """Ensure isort preserves form feed as a valid blank line."""
+    test_input = 'import os\nimport sys\n\n\f\nprint("Hello, world!")\n'
+    assert isort.code(test_input) == test_input
+
+
 def test_extra_blank_line_added_nested_imports_issue_1290():
     """Ensure isort doesn't add unnecessary blank lines above nested imports.
     See: https://github.com/pycqa/isort/issues/1290