PrettyPrinter

Warnings

• breaking The default behavior for dictionary key sorting changed in version 0.8.0. Previously, keys were sorted like in the standard library's `pprint` module. Now, they default to insertion order (for CPython 3.6+). To revert to sorted keys, use the `sort_dict_keys` argument in `pprint` or configure it in `PrettyContext` for custom printers.
  Fix: If sorted dictionary keys are required, explicitly pass `sort_dict_keys=True` to `pprint()` or `pformat()`, or set this option in your custom `PrettyContext`.
• gotcha There are two distinct Python libraries with similar names: the built-in `pprint` module and the external `prettyprinter` library. Users often confuse the two. `prettyprinter` offers enhanced features like syntax highlighting, a more flexible API, and extensibility, which the standard library module does not.
  Fix: Always explicitly `from prettyprinter import pprint` to ensure you are using the external library. Avoid `import pprint` if you intend to use `prettyprinter`'s features, as it will import the standard library module.
• gotcha For `prettyprinter` to automatically format output in Python shells (like IPython or the default Python REPL) or for it to pretty-print types from other popular libraries (e.g., `dataclasses`, `attrs`, `django`), you must explicitly call `install_extras()`. Without this, only basic types will be pretty-printed, and shell integration will not occur.
  Fix: Call `from prettyprinter import install_extras; install_extras(['python'])` for the default shell or `install_extras(['ipython'])` for IPython. You can also specify other libraries like `install_extras(include=['dataclasses', 'requests'])`. For persistent shell integration, consider setting the `PYTHONSTARTUP` environment variable.
• deprecated When defining custom pretty printers, the `PrettyContext.set` method was deprecated in favor of `PrettyContext.assoc`. While `set` might still work in older versions, `assoc` is the recommended and clearer method for modifying context values.
  Fix: Update your custom pretty printer definitions to use `ctx.assoc(...)` instead of `ctx.set(...)` for context manipulation.
• gotcha When trying to pretty-print custom objects, simply defining a `__repr__` method on your class might not fully leverage `prettyprinter`'s capabilities or might even be overridden by `prettyprinter`'s default handling for certain base types. The library's declarative approach provides a more robust way.
  Fix: For optimal and consistent pretty-printing of custom types, use `prettyprinter.register_pretty` with a dedicated pretty printer function, combined with `pretty_call`, rather than solely relying on `__repr__`.

Install

• pip install prettyprinter Install stable version

Imports

• pprint

  from prettyprinter import pprint

  To use prettyprinter's main function, explicitly import `pprint` from `prettyprinter` to avoid conflict with the standard library's `pprint` module.
• install_extras

  from prettyprinter import install_extras

  Used for enabling integrations with shells (like IPython) or other third-party libraries (e.g., Django, NumPy, Requests).
• register_pretty

  from prettyprinter import register_pretty, pretty_call

  These functions are used when defining custom pretty-printing rules for your own Python types.

Quickstart

This quickstart demonstrates basic pretty-printing of a nested dictionary and how to define custom pretty-printing rules for your own classes using `@register_pretty`. It also notes how to enable shell integrations for a more persistent pretty-printing experience.

from prettyprinter import pprint, register_pretty, pretty_call

# Basic pretty-printing of a nested dictionary
data = {
    'name': 'PrettyPrinter Example',
    'details': {
        'id': 12345,
        'items': [
            {'item_id': 'A1', 'value': 100.5, 'tags': ['new', 'sale']},
            {'item_id': 'B2', 'value': 200, 'tags': ['old']},
            {'item_id': 'C3', 'value': 50.75, 'tags': []}
        ],
        'status': 'active'
    },
    'configs': [
        {'key': 'timeout', 'value': 30},
        {'key': 'retries', 'value': 5}
    ]
}

print('--- Standard print ---')
print(data)
print('\n--- PrettyPrinter output ---')
pprint(data)

# Custom pretty-printing for a user-defined class
class MyObject:
    def __init__(self, name, values):
        self.name = name
        self.values = values

@register_pretty(MyObject)
def pretty_my_object(value, ctx):
    return pretty_call(
        ctx,
        MyObject,
        name=value.name,
        values=value.values
    )

my_instance = MyObject('CustomItem', [{'x': 1, 'y': 2}, {'z': 3}])
print('\n--- Custom object pretty-printing ---')
pprint(my_instance)

# To enable shell integration (e.g., for `ipython` or default python shell):
# from prettyprinter import install_extras
# install_extras(['ipython']) # or ['python']
# {'a': 1, 'b': 2} # will now be pretty-printed in the shell