Wadler-Lindig Pretty Printer

0.1.7 · active · verified Thu Apr 09

Wadler-Lindig is a Python library that provides a pretty-printer based on the Wadler–Lindig algorithm. It serves as an alternative to the built-in `pprint.pprint`, aiming to produce output that consumes less horizontal space, which is particularly useful for complex custom types, error messages, or nested data structures. The library is characterized by its compact implementation, support for multi-line strings and ANSI escape codes, and zero runtime dependencies. The current version is 0.1.7, and it appears to be actively maintained.

Warnings

gotcha The `width` argument in `pprint` and `pformat` is a 'best-effort' maximum. It may be exceeded if there are unbroken pieces of text (e.g., long strings) that are inherently wider than the specified width.
Fix: Design custom `__pdoc__` methods or preprocess long strings if strict width adherence is critical for specific parts of the output.
gotcha Customizing pretty-printing for your own types typically uses the `__pdoc__` method, which is specific to this library. For third-party types you don't own, use the `custom` argument in `wl.pprint` or `wl.pformat` instead of `__pdoc__`.
Fix: For your types, implement `def __pdoc__(self, **kwargs) -> wl.AbstractDoc: ...`. For external types, pass `custom=your_custom_function` to the pretty-printing calls.
gotcha This library is designed for pretty-formatting Python *objects* at runtime, similar to the built-in `pprint` module. It is *not* a source code formatter like Black or Rustfmt, and should not be used for reformatting Python source files.
Fix: Understand its purpose as an object introspection and display tool. For source code formatting, use dedicated tools like Black or Ruff.
gotcha Output format differs from Python's built-in `pprint.pprint`. `wadler-lindig` prioritizes reducing horizontal space and often indents more aggressively. It also provides a concise summary for NumPy arrays by default (e.g., `f64[2,3](numpy)`).
Fix: If expecting exact `pprint` behavior, be aware of these differences. For NumPy array verbosity, set `short_arrays=False` in `pprint`/`pformat` calls. Adapt custom pretty-printing logic if migrating from `pprint`.

Install

pip install wadler-lindig Install stable version

Imports

pprint
```
import wadler_lindig as wl
wl.pprint(obj)
```
It is recommended to import `wadler_lindig` with an alias (e.g., `wl`) to avoid naming conflicts with Python's standard `pprint` module and to clearly distinguish its functions.
pformat
```
import wadler_lindig as wl
formatted_string = wl.pformat(obj)
```
Used to get a pretty-formatted string instead of printing directly to stdout.

Quickstart

This quickstart demonstrates basic usage of `wadler_lindig.pprint` and `pformat` with a dataclass containing a list and a NumPy array. It also illustrates how to customize the pretty-printing for a custom class using the `__pdoc__` method. Note that `numpy` is used for demonstration purposes, but is not a core dependency of the `wadler-lindig` library itself.

import dataclasses
import numpy as np
import wadler_lindig as wl

@dataclasses.dataclass
class MyDataclass:
    x: list[str]
    y: np.ndarray

obj = MyDataclass(
    x=["lorem", "ipsum", "dolor sit amet", "consectetur", "adipiscing elit"],
    y=np.zeros((2, 3))
)

print("\n--- Default pprint output ---")
print(obj)

print("\n--- wadler_lindig.pprint output (width=30, indent=4) ---")
wl.pprint(obj, width=30, indent=4)

print("\n--- wadler_lindig.pformat output (width=20) ---")
formatted_str = wl.pformat(obj, width=20, indent=2)
print(formatted_str)

# Example of custom pretty-printing for a non-dataclass type
class MyCustomClass:
    def __init__(self, value):
        self.value = value
    
    def __pdoc__(self, **kwargs) -> wl.AbstractDoc:
        return wl.TextDoc(f"<MyCustomClass: {self.value}> ")

    def __repr__(self):
        return wl.pformat(self, width=80)

custom_obj = MyCustomClass(123)
print("\n--- Custom object with __pdoc__ ---")
wl.pprint(custom_obj)

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