better dedent

It's like textwrap.dedent, but with added t-string support.

The problem: interpolating before dedenting

Have you ever used textwrap.dedent with an f-string that has newline characters in a replacement field?

For example, given this code string (which has newlines in it):

code = r"""
def strip_each(lines):
    new_lines = []
    for line in lines:
        new_lines.append(line.rstrip("\n"))
    return new_lines
""".strip("\n")

Using textwrap.dedent with an f-string that uses code in a replacement field results in very strange indentation:

>>> print(dedent(f"""\
...     Example function:
...         {code}
...
...     That function was NOT indented properly!"""))
Example function:
    def strip_each(lines):
new_lines = []
for line in lines:
    new_lines.append(line.rstrip("\n"))
return new_lines

The problem is that f-strings immediately interpolate their replacement fields.

That code string is injected into the new string before dedent has a chance to even look at the string. By the time textwrap.dedent does its dedenting, the weirdness has already happened.

The solution: interpolating after dedenting

Passing a t-string to the better_dedent.dedent function allows the replacement fields to maintain their original indentation level.

Using the same code string as before:

code = r"""
def strip_each(lines):
    new_lines = []
    for line in lines:
        new_lines.append(line.rstrip("\n"))
    return new_lines
""".strip("\n")

The better_dedent.dedent function will dedent the t-string and then inject the replacement field, resulting in much more sensible indentation:

>>> print(dedent(t"""\
...     Example function:
...         {code}
...
...     That function was indented properly!""")
...
Example function:
    def strip_each(lines):
        new_lines = []
        for line in lines:
            new_lines.append(line.rstrip("\n"))
        return new_lines

That function was indented properly!

Using a t-string allows for dedenting the whole string before the replacement fields are inserted and then inserting the replacement fields.

Note that if an f-string is passed to better_dedent.dedent, it will simply delegate to textwrap.dedent.

undent

This package also includes an undent function, which will strip a leading newline (note the lack of \ after t"""):

>>> print(undent(t"""
...     Example function:
...         {code}
...     That function was indented properly!"""))
Example function:
    def strip_each(lines):
        new_lines = []
        for line in lines:
            new_lines.append(line.rstrip("\n"))
        return new_lines
That function was indented properly!

The undent function will also strips a trailing newline by default:

>>> print(undent(t"""
...     Example function:
...         {code}
...     That function was indented properly!
... """))
Example function:
    def strip_each(lines):
        new_lines = []
        for line in lines:
            new_lines.append(line.rstrip("\n"))
        return new_lines
That function was indented properly!
>>> print("Note that there's no blank line above this prompt")
Note that there's no blank line above this prompt

Passing strip_trailing=False to undent will suppress trailing newline removal.

Installation

pip install better-dedent

Or if you have uv installed and you'd like to play with it right now:

uvx --with better-dedent python

You can then import dedent and undent like this:

from better_dedent import dedent, undent

And try them out:

code = r"""
def strip_each(lines):
    new_lines = []
    for line in lines:
        new_lines.append(line.rstrip("\n"))
    return new_lines
""".strip("\n")

text = undent(t"""
    Here is some example code:

        {code}

    That indentation worked out nicely!
""")
print(text)

License

better-dedent is distributed under the terms of the MIT license.