m-o

A command line tool for parsing Python dataclass reprs and pretty-printing them. The name is based on the WALL-E character M-O, a robot who liked to clean things up.

Example

# my_data.py

@dataclass
class Dog:
    name: str
    age: int
    friends: List[str]

pip = Dog("Pip", 7, ["Quincy", "Digger"])
print(pip)

$ # without m-o:
$ python my_data.py
Dog(name="Pip", age=7, friends=["Quincy", "Digger"])

$ # with m-o:
$ python my_data.py | m-o
Dog(
    name="Pip",
    age=7,
    friends=[
        "Quincy",
        "Digger",
    ],
)

why tho?

Python's pprint.pprint function allows common values (tuples, lists, dicts, etc.) to be pretty-printed, but does not know how to format Python 3.7's dataclasses. I use dataclasses pretty frequently, and often need to debug deeply nested trees of dataclasses. The __repr__ method on dataclasses displays everything on one line which is difficult to read.

Rather than implementing pprint.pprint for your dataclasses (who even knows how to do this anyway?), just print out the value and pipe it into this tool. The data structure will be pretty-printed to your terminal.

Installation

$ cargo install --git https://github.com/eignnx/m-o

Why not cargo install m-o?

Currently, m-o depends on an unreleased alpha version of pretty.rs. This means cargo install m-o doesn't work because the crate cannot be published on crates.io.

If you don't mind using an older version of the crate, you can install version 0.1.5 (which has a less sophisticated layout algorithm) from crates.io with this command:

$ cargo install m-o

(Planned/Current) Features

• Parse string escape characters (0.1.5)
• Use "Wadler-style" pretty-printing algorithm (0.1.6)
• Use stable version of pretty.rs
• Add command-line options for:
  • Indentation level (currently 4 spaces) (0.1.7)
  • Target width (number of columns) (0.1.7)
• Better error messages when parsing fails
• Allow non-keyword arguments in constructors (ex: Dog('Pip', age=7)) (0.1.7)
• Support multi-identifier paths in symbols (ex: datetime.datetime) (0.1.7)