Lib/pprint.py (part 3)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/pprint.py ↗

This annotation covers the collection formatters. See lib_pprint2_detail for PrettyPrinter.__init__, pformat, _format, and the repr dispatch.

Map

Lines	Symbol	Role
1-80	_pprint_dict	Format {k: v, ...} with optional sorting
81-160	_pprint_set / _pprint_frozenset	Format sets with {...} or frozenset({...})
161-240	_pprint_tuple	Format tuples; single-element gets trailing comma
241-320	_pprint_dataclass	Format dataclass instances field-by-field
321-500	Width/depth logic	_format_items, indent stack, max_width

Reading

_pprint_dict

# CPython: Lib/pprint.py:194 PrettyPrinter._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_tuple)
    else:
        items = object.items()
    self._format_dict_items(items, stream, indent, allowance + 1,
                            context, level)
    write('}')

sort_dicts=True (the default) sorts keys with _safe_tuple to handle mixed-type keys gracefully. Pass sort_dicts=False to preserve insertion order, which is useful when dict order encodes meaning (configuration, JSON round-trips).

_pprint_set

# CPython: Lib/pprint.py:230 PrettyPrinter._pprint_set
def _pprint_set(self, object, stream, indent, allowance, context, level):
    if not len(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
    self._format_items(sorted(object, key=_safe_key),
                       stream, indent, allowance + len(endchar),
                       context, level)
    stream.write(endchar)

Empty sets can't use {} (that's a dict literal), so repr(set()) returns 'set()'. Non-empty sets are always sorted for deterministic output. frozenset wraps in frozenset({...}).

_pprint_tuple

# CPython: Lib/pprint.py:260 PrettyPrinter._pprint_tuple
def _pprint_tuple(self, object, stream, indent, allowance, context, level):
    if len(object) == 1:
        stream.write('(')
        self._format(object[0], stream, indent + 1, allowance + 2,
                     context, level)
        stream.write(',)')
    else:
        self._format_items(object, stream, indent + 1, allowance + 1,
                           context, level, '(', ')')

Single-element tuples require the trailing comma. Multi-element tuples delegate to _format_items for width-aware line breaking.

_pprint_dataclass

# CPython: Lib/pprint.py:290 PrettyPrinter._pprint_dataclass
def _pprint_dataclass(self, object, stream, indent, allowance, context, level):
    cls_name = object.__class__.__name__
    stream.write(cls_name + '(')
    indent += len(cls_name) + 1
    items = [(f.name, getattr(object, f.name))
             for f in dataclasses.fields(object)
             if f.repr]
    self._format_dict_items(items, stream, indent, allowance + 1,
                            context, level, '=')
    stream.write(')')

Dataclasses are formatted as ClassName(field=value, ...). Only fields with repr=True (the default) are included. The separator is = not : to match dataclass repr style.

gopy notes

PrettyPrinter is module/pprint.Printer in module/pprint/module.go. _pprint_dict uses objects.DictItems and an optional sort. _pprint_set calls objects.SetToSortedSlice. _pprint_dataclass iterates dataclasses.Fields via the dataclasses module port.