Skip to content

FAQ¤

What is the difference to the built-in pprint library?¤

  1. The main difference is that the Wadler–Lindig algorithm produces output like
MyDataclass(
  x=SomeNestedClass(
    y=[1, 2, 3]
  )
)

In contrast pprint produces output like

MyDataclass(x=SomeNestedClass(y=[1,
                                 2,
                                 3]))

which consumes a lot more horizontal space.

  1. By default we print NumPy arrays / PyTorch tensors / etc. in a concise form e.g. f32[2,3](numpy) to denote a NumPy array with shape (2, 3) and dtype float32. (Set short_arrays=False to disable this.)

  2. We provide support for customising the pretty-printed representations of your custom types. Typically this is done via:

    import wadler_lindig as wl

class MyAmazingClass:
    def __pdoc__(self, **kwargs) -> wl.AbstractDoc:
        ...  # Create your pretty representation here!

    def __repr__(self):
        # Calls `__pdoc__` and then formats to a particular width.
        return wl.pformat(self, width=80)

    In addition we support a wadler_lindig.pprint(..., custom=...) argument, if you don't own the type and so cannot add a __pdoc__ method.

What is the difference to black or rust format?¤

The above are formatters for your source code. This wadler_lindig library is intended as an alternative to the built-in pprint library, which pretty-format Python objects at runtime.

How do I emit markup (e.g. HTML tags) without it counting towards the line width?¤

Use TextDoc(..., width=False). The text is emitted as-is but takes no space when deciding where to break lines:

import wadler_lindig as wl

def tag(t):
    return wl.TextDoc(t, width=False)

doc = tag("<b>") + wl.TextDoc("hello") + tag("</b>")

Escaping any special characters (such as a literal <) in your own text is up to you.