Lib/pprint.py (part 2)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/pprint.py ↗

This annotation covers the per-type formatting methods. See lib_pprint_detail for pprint, pformat, PrettyPrinter.__init__, _format, and _repr.

Map

Lines	Symbol	Role
1-80	_pprint_dict	Format a dict with sorted keys and indented values
81-180	_pprint_ordered_dict	Format OrderedDict preserving insertion order
181-300	_pprint_list / _pprint_tuple	Format list/tuple with per-element recursion
301-420	_pprint_set / _pprint_frozenset	Format set/frozenset with sorted elements
421-560	_pprint_dataclass	Format dataclass instances field by field
561-700	_format_items	Shared helper for sequences and mappings

Reading

_pprint_dict

# CPython: Lib/pprint.py:280 _pprint_dict
def _pprint_dict(self, object, stream, indent, allowance, context, level):
    write = stream.write
    write('{')
    if self._sort_dicts:
        items = sorted(object.items(), key=_safe_key)
    else:
        items = object.items()
    self._format_dict_items(items, stream, indent, allowance + 1,
                            context, level)
    write('}')

When sort_dicts=True (the default), dict keys are sorted using a _safe_key wrapper that handles mixed-type keys without raising TypeError. Large dicts are split across lines with each key-value pair indented.

_format_items

# CPython: Lib/pprint.py:560 _format_items
def _format_items(self, items, stream, indent, allowance, context, level):
    write = stream.write
    indent += self._indent_per_level
    delimnl = ',\n' + ' ' * indent
    delim = ''
    max_width1 = max_width = self._width - indent + 1
    for item in items:
        # Try to fit item on the current line
        w = len(delim) + self._repr(item, context, level).width
        if self._compact and w <= max_width:
            write(delim)
            self._repr(item, context, level).write(stream)
            max_width -= w
        else:
            write(delim)
            write('\n' + ' ' * indent)
            self._format(item, stream, indent, allowance, context, level + 1)
            max_width = max_width1
        delim = ','

_format_items is the shared loop used by list, tuple, set, and frozenset formatters. compact=True packs items on the same line until the width limit is reached, then wraps.

_pprint_dataclass

# CPython: Lib/pprint.py:430 _pprint_dataclass
def _pprint_dataclass(self, object, stream, indent, allowance, context, level):
    cls_name = object.__class__.__name__
    indent += len(cls_name) + 1
    items = [(f.name, getattr(object, f.name))
             for f in dataclasses.fields(object)
             if f.repr]
    return self._format_namespace_items(items, stream, indent, allowance,
                                        context, level)

Dataclass instances are formatted as ClassName(field=value, ...). Only fields with repr=True (the default) are included.

_pprint_set

# CPython: Lib/pprint.py:310 _pprint_set
def _pprint_set(self, object, stream, indent, allowance, context, level):
    if not object:
        stream.write(repr(object))
        return
    typ = object.__class__
    if typ is set:
        stream.write('{')
        endchar = '}'
    else:
        stream.write(typ.__name__ + '({')
        endchar = '})'
        indent += len(typ.__name__) + 1
    object = sorted(object, key=_safe_key)
    self._format_items(object, stream, indent, allowance, context, level)
    stream.write(endchar)

Sets are sorted for deterministic output. Empty sets print as set() since {} would be an empty dict.

gopy notes

pprint is pure Python. PrettyPrinter dispatch is via a _dispatch dict mapping type.__repr__ to handler functions. _pprint_dataclass calls dataclasses.fields from module/dataclasses. _safe_key is a Go struct in module/pprint/module.go with a custom Less that catches panics from comparison.