Preserve blank line formatting

README.md

@@ -12,9 +12,12 @@
 
 ---
 
-A custom ConfigParser class that preserves comments and option casing when writing loaded config out.
+A custom ConfigParser class that preserves comments and most formatting when
+writing loaded config out.
 
-This library gives you a custom class of the standard library's `configparser.ConfigParger` which will preserve the comments of a loaded config file when writing that file back out.
+This library gives you a custom class of the standard library's
+`configparser.ConfigParger` which will preserve the comments of a loaded config
+file when writing that file back out.
 
 ---
 
@@ -58,7 +61,12 @@ with open("myconfig.ini", "w") as savefile:
 
 ## Results
 
-We favor the line spacing choices of the `ConfigParser` class so the input format may not be preserved completely. However, the comments will be preserved.
+There is the attempt to retain the original format. Known formats that will not
+be preserved:
+
+1. Indents will not be preserved outside of multi-line values
+2. Spacing around assignments will be normalized.
+3. Casing of all options will be written as lowercase.
 
 ### Before
 
@@ -83,7 +91,6 @@ multi-line=
 	value03
 closing=0
 # Trailing comment
-
 ```
 
 ### After
@@ -97,9 +104,10 @@ foo = bar
 trace = false
 logging = true
 ; This is a comment as well
+
 # so we need to track all of them
-; and many could be between things
 
+; and many could be between things
 [NEW SECTION]
 # Another comment
 multi-line =
@@ -108,5 +116,4 @@ multi-line =
 	value03
 closing = 0
 # Trailing comment
-
 ```

src/commentedconfigparser/commentedconfigparser.py

@@ -17,6 +17,7 @@
 __all__ = ["CommentedConfigParser"]
 
 _COMMENT_PATTERN = re.compile(r"^\s*[#|;]\s*(.*)$")
+_BLANK_LINE_PATTERN = re.compile(r"^\s*$")
 _COMMENT_OPTION_PATTERN = re.compile(r"^(\s*)?__comment_\d+\s?[=|:]\s?(.*)$")
 _KEY_PATTERN = re.compile(r"^(.+?)\s?[=|:].*$")
 _SECTION_PATTERN = re.compile(r"^\s*\[(.+)\]\s*$")
@@ -98,6 +99,11 @@ def _translate_comments(self, content: list[str]) -> str:
                 # are handled by the parent and retain order of insertion.
                 line = f"__comment_{self.__file_index}{idx}={line.lstrip()}"
 
+            elif _BLANK_LINE_PATTERN.match(line):
+                # Blank lines cannot be stripped or the newline char will
+                # be lost which causes issues downstream.
+                line = f"__comment_{self.__file_index}{idx}={line}"
+
             elif _KEY_PATTERN.match(line) or _SECTION_PATTERN.match(line):
                 # Strip the left whitespace from sections and keys. This will
                 # leave only multiline values with leading whitespace preventing
@@ -121,13 +127,14 @@ def _restore_comments(self, content: str) -> str:
             rendered += self.__header_block
 
         for line in content.splitlines():
+            if not line:
+                # Skip the provided empty lines and use our own instead
+                continue
+
             comment_match = _COMMENT_OPTION_PATTERN.match(line)
             if comment_match:
                 line = comment_match.group(2)
 
             rendered.append(line + "\n")
 
-        # Remove extra trailing newline
-        rendered[-1] = rendered[-1].rstrip()
-
         return "".join(rendered)

tests/empty_comments_expected.ini

@@ -4,11 +4,14 @@
 
 [DEFAULT]
 foo = bar
+
 # Comment here
 #
 bar = foo
 ;
 ; Comment here too
 
+
 [BIZ]
 baz = bar
+

tests/empty_comments_input.ini

@@ -14,3 +14,4 @@ bar = foo
 
 [BIZ]
 baz=bar
+

tests/pydocs_expected.ini

@@ -25,6 +25,7 @@ empty string value here =
 [You can use comments]
 # like this
 ; or this
+
 # By default only in an empty line.
 # Inline comments can be harmful because they prevent users
 # from using the delimiting characters as parts of values.

tests/regression_original_expected.ini

@@ -6,9 +6,10 @@ foo = bar
 trace = false
 logging = true
 ; This is a comment as well
+
 # so we need to track all of them
-; and many could be between things
 
+; and many could be between things
 [NEW SECTION]
 foo = bar
 # Unique foo