How to Enforce Indentation Rules From .editorconfig in Python

A mock function that reads .editorconfig-style indentation rules (spaces or tabs, size) and fixes indentation in source code lines by tracking brace depth.

Medium Python 3.9+ Aug 9, 2026 Modern tooling 14 views 0 copies

editorconfig indentation formatting tooling

Python code

51 lines

Python 3.9+

def enforce_indent(editorconfig_rules, file_content):
    """
    Mock function to enforce indentation rules from .editorconfig.
    Returns the content with indentation fixed (or unchanged if already compliant).
    """
    indent_style = editorconfig_rules.get("indent_style", "spaces")
    indent_size = int(editorconfig_rules.get("indent_size", "4"))
    
    # Determine expected indentation unit
    if indent_style == "tab":
        expected = "\t"
        pattern = r"^\s*"
    else:
        expected = " " * indent_size
        pattern = r"^\s*"
    
    lines = file_content.splitlines(keepends=True)
    fixed_lines = []
    indent_level = 0
    
    for line in lines:
        stripped = line.lstrip()
        if not stripped:
            fixed_lines.append("\n")
            continue
        
        # Adjust indent level based on braces (simple mock heuristic)
        if stripped.startswith("}"):
            indent_level = max(0, indent_level - 1)
        
        # Build the correct indentation
        if indent_style == "tab":
            new_indent = expected * indent_level
        else:
            new_indent = expected * indent_level
        
        fixed_lines.append(new_indent + stripped)
        
        # Increment level after opening brace
        if stripped.endswith("{"):
            indent_level += 1
    
    return "".join(fixed_lines)


if __name__ == "__main__":
    rules = {"indent_style": "spaces", "indent_size": "2"}
    sample_code = "function test() {\nif (true) {\nconsole.log('hi');\n}\n}\n"
    
    result = enforce_indent(rules, sample_code)
    print(result)

Output

stdout

function test() {
  if (true) {
    console.log('hi');
  }
}

How it works

The function parses .editorconfig rules for indent_style and indent_size, then rebuilds each non-empty line with the correct leading whitespace. It tracks indentation level by counting opening and closing braces {/} on each line — a simple heuristic that works for C-like syntax. The regex pattern r"^\s*" is used only to strip existing leading whitespace via lstrip(). Because empty lines are replaced with a plain newline, whitespace-only lines are normalized instead of preserved. This mock mirrors how tools like autopep8 or prettier apply formatting rules before a commit.

Common mistakes

Using lstrip() and then re-adding indentation only for non-empty lines, losing intentional blank-line whitespace
Forgetting to handle closing braces before computing the current indent level, causing off-by-one indentation
Assuming indent_size is always an integer without coercing it, which breaks when .editorconfig has `indent_size = tab`

Variations

Use `textwrap.dedent` or a custom tokenizer to handle indentation more robustly for nested structures beyond braces
Parse .editorconfig files directly with the `configparser` module and apply rules per-file glob patterns

Real-world use cases

Pre-commit hook that normalizes indentation across a team's codebase before files are staged.
IDE or editor plugin that reformats pasted code to match the project's .editorconfig settings.
CI pipeline that checks and auto-fixes indentation drift in pull requests for mixed-contributor repos.

How to Enforce Indentation Rules From .editorconfig in Python

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Modern tooling

Tutorials

Quizzes

Python code

Output

How it works

Common mistakes

Variations

Real-world use cases

More from Modern tooling

Keep learning

Tutorials

Quizzes