trimmargin ✂️📏

Kotlin-style trimMargin and friends for Python — with a tiny CLI

Features

• 🔄 Normalizes line endings to \n
• 🧼 Drops first/last blank lines (edges only, not interior)
• 🧲 trim_margin() strips leading whitespace + a margin prefix (default |)
• 🔧 replace_indent_by_margin() like Kotlin’s, with a custom replacement indent
• 🪄 trim_indent() / replace_indent() built on textwrap.dedent/indent
• ➕ prepend_indent() behaves like Kotlin (blank-line quirk covered)

Installation

# uv (recommended)
uv pip install trimmargin

# or pip
pip install trimmargin

Quick Start

from trimmargin import trim_margin, replace_indent_by_margin

text = """
    |hello
    |world
"""

print(trim_margin(text))
# hello
# world

print(replace_indent_by_margin(text, new_indent=">>> "))
# >>> hello
# >>> world

Behavior Notes

• If a line’s first non-whitespace char starts the margin prefix, both the leading whitespace and the prefix are removed; other lines are unchanged.
• Only the first and last blank lines are dropped.
• Input may use \r\n, \n, or \r; output uses \n.

CLI Usage 🚀

The trimmargin command reads a file or stdin and writes to stdout.

# default: trim-margin on stdin using prefix "|"
trimmargin < input.txt

# file input
trimmargin input.txt

# modes
trimmargin --mode replace-by-margin --new-indent ">>> " input.txt
trimmargin --mode trim-indent < input.txt
trimmargin --mode replace-indent --new-indent "  " < input.txt
trimmargin --mode prepend --indent ">> "

# change margin prefix
trimmargin --prefix "§" < input.txt

# version
trimmargin --version

Modes

• trim-margin (default): remove leading whitespace + prefix

• replace-by-margin: same detection as above, then add new-indent

• trim-indent: remove common indent via textwrap.dedent

• replace-indent: dedent then indent non-blank lines with new-indent

• prepend: prepend indent to non-blank lines; blank-line quirk matches Kotlin:

  • if blank and len(line) < len(indent): line becomes exactly indent
  • else: leave blank line unchanged

Development (uv) 🧑‍💻

# setup
uv sync --extra dev

# tests
uv run pytest

# lint & types
uv run ruff check .
uv run mypy src

# format
uv run ruff format .

# build & publish
uv build
uv publish

Why This Exists ❓

textwrap.dedent/indent are great, but Kotlin’s margin-aware trimming is handy for multiline literals embedded in code and docs.