Lib/pprint.py (part 4)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/pprint.py ↗

This annotation covers the per-type formatting methods. See lib_pprint3_detail for PrettyPrinter.__init__, pprint, pformat, and cycle detection.

Map

Lines	Symbol	Role
1-80	_pprint_dict	Format {'key': value, ...} with indentation
81-160	_pprint_list	Format [item, ...] with indentation
161-240	_pprint_tuple	Format (item, ...) — trailing comma for singletons
241-360	compact mode	Pack multiple items on one line if they fit
361-500	_pprint_dataclass	Dataclass-aware formatting

Reading

_pprint_dict

# CPython: Lib/pprint.py:220 _pprint_dict
def _pprint_dict(self, object, stream, indent, allowance, context, level):
    write = stream.write
    indent += self._indent_per_level
    items = sorted(object.items(), key=_safe_tuple) if self._sort_dicts else object.items()
    self._format_dict_items(items, stream, indent, allowance, context, level)

def _format_dict_items(self, items, stream, indent, allowance, context, level):
    write = stream.write
    indent += self._indent_per_level
    delimnl = ',\n' + ' ' * indent
    last_index = len(items) - 1
    for i, (key, ent) in enumerate(items):
        write(repr(key) + ': ')
        self._format(ent, stream, indent + len(repr(key)) + 2, ...)
        if i != last_index:
            write(delimnl)

sort_dicts=True (the default before 3.8) sorts keys. Each value is formatted recursively with increased indentation. The allowance parameter is how many more characters can fit on the last line.

_pprint_list

# CPython: Lib/pprint.py:250 _pprint_list
def _pprint_list(self, object, stream, indent, allowance, context, level):
    stream.write('[')
    self._format_items(object, stream, indent + 1, allowance + 1, context, level)
    stream.write(']')

def _format_items(self, items, stream, indent, allowance, context, level):
    write = stream.write
    indent += self._indent_per_level - 1
    delimnl = ',\n' + ' ' * indent
    for i, ent in enumerate(items):
        if i:
            write(delimnl)
        self._format(ent, stream, indent, ...)

Each item is formatted on its own line when the list doesn't fit on one line. The indent + 1 for '[' accounts for the bracket character itself.

compact mode

# CPython: Lib/pprint.py:300 _format_items with compact
def _format_items(self, items, stream, indent, allowance, context, level):
    if self._compact:
        # Try to pack multiple items on a line
        max_width = self._width - indent + 1
        words = []
        for item in items:
            word = self._repr(item, context, level)
            if len(word) > max_width:
                break
            words.append(word)
        ...

pprint(data, compact=True) packs multiple short items on the same line. Items that don't fit on the current line start a new line. Items longer than max_width break out of compact mode.

_pprint_dataclass

# CPython: Lib/pprint.py:380 _pprint_dataclass (3.10+)
def _pprint_dataclass(self, object, stream, indent, allowance, context, level):
    cls_name = type(object).__name__
    stream.write(cls_name + '(')
    items = [(f.name, getattr(object, f.name))
             for f in dataclasses.fields(object)
             if f.repr]
    self._format_dict_items(items, stream, indent + len(cls_name) + 1, ...)
    stream.write(')')

Dataclasses are formatted as ClassName(field=value, ...). Only fields with repr=True (the default) are shown. Nested dataclasses are formatted recursively.

gopy notes

_pprint_dict is module/pprint.PrettyPrinter.pprintDict in module/pprint/module.go. Items are sorted via objects.DictKeys then sort.Slice. compact mode checks strings.Builder length vs width. _pprint_dataclass calls module/dataclasses.Fields to get the field list.