Lib/pprint.py (part 5)

Source:

cpython 3.14 @ ab2d84fe1023/Lib/pprint.py

This annotation covers collection-specific formatting. See lib_pprint4_detail for PrettyPrinter.pformat, _repr, and depth control.

Map

Lines	Symbol	Role
1-80	`_pprint_list`	Format a list with wrapping
81-160	`_pprint_dict`	Format a dict in sorted key order
161-240	`_pprint_dataclass`	Format a dataclass (3.10+)
241-340	`_pprint_tuple`	Format a tuple
341-400	Compact mode	Fit multiple items per line

Reading

`_pprint_list`

# CPython: Lib/pprint.py:282 _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(']')

List formatting delegates to _format_items which tries to fit items on one line first. If the representation exceeds self._width, it falls back to one item per line. The allowance accounts for the closing ].

`_pprint_dict`

# CPython: Lib/pprint.py:310 _pprint_dict
def _pprint_dict(self, object, stream, indent, allowance, context, level):
    write = stream.write
    write('{')
    if self._indent_per_level > 1:
        write((self._indent_per_level - 1) * ' ')
    length = len(object)
    if length:
        self._format_dict_items(object.items() if self._sort_dicts
                                else object.items(),
                                stream, indent, allowance, context, level)
    write('}')

pprint.pprint({'b': 2, 'a': 1}) sorts keys by default (sort_dicts=True). sort_dicts=False (added in 3.8) preserves insertion order. Each key-value pair is formatted with key: value, with long values wrapped onto the next line at the value's indentation.

`_pprint_dataclass`

# CPython: Lib/pprint.py:340 _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_namespace_items(items, stream, indent, allowance, context, level)
    stream.write(')')

pprint.pprint(Point(x=1, y=2)) prints Point(x=1, y=2) for small objects or a multi-line form for complex nested dataclasses. Only fields with repr=True (the default) are included.

Compact mode

# CPython: Lib/pprint.py:420 _format_items (compact excerpt)
def _format_items(self, items, stream, indent, allowance, context, level):
    write = stream.write
    indent += self._indent_per_level
    delimnl = ',\n' + ' ' * indent
    delim = ''
    max_width = self._width - indent + 1
    width = max_width
    for item in items:
        ...
        if self._compact:
            rep = self._repr(item, context, level)
            if width >= len(rep) + 2:
                # Fits on current line
                write(delim + rep)
                width -= len(rep) + 2
                delim = ', '
                continue
        write(delim + '\n' + ' ' * indent)
        ...

compact=True (added in 3.8) packs multiple items onto the same line until the width limit is reached. Compact mode is useful for dense output of large collections where the default one-item-per-line is too verbose.

gopy notes

pprint is a pure-Python module; gopy runs it directly. _pprint_list, _pprint_dict, and _pprint_dataclass are registered in _dispatch at module initialization. _pprint_dataclass uses dataclasses.fields which routes to module/dataclasses.Fields. All output goes to a io.StringIO or sys.stdout via objects.FileWrite.

Map​

Reading​

_pprint_list​

_pprint_dict​

_pprint_dataclass​

Compact mode​

gopy notes​

Map