Lib/reprlib.py

Source:

cpython 3.14 @ ab2d84fe1023/Lib/reprlib.py ↗

reprlib provides a Repr class that generates size-limited string representations, truncating long sequences and strings with .... It is used by pprint, the interactive REPL, and logging infrastructure to prevent enormous outputs from hanging or flooding output.

Map

Lines	Symbol	Role
1-30	recursive_repr	Decorator that returns '...' for recursive calls
31-80	Repr class attributes	maxlevel, maxdict, maxlist, maxlong, maxstring, etc.
81-160	Repr.repr* methods	Per-type repr dispatch
161-178	aRepr, repr	Module-level singleton and top-level function

Reading

recursive_repr

Decorates __repr__ methods to detect and break recursion. On re-entry it returns fillvalue (default '...') instead of recursing.

# CPython: Lib/reprlib.py:9 recursive_repr
def recursive_repr(fillvalue='...'):
    def decorating_function(user_function):
        wrapper = _recursive_repr(fillvalue)(user_function)
        return wrapper
    return decorating_function

Internally uses a thread-local set of object IDs to detect when the same object is being repr'd while already repr'ing it.

Repr.repr1

The dispatcher. Calls repr_TYPE if defined, otherwise falls back to builtins.repr with a level check.

# CPython: Lib/reprlib.py:90 Repr.repr1
def repr1(self, x, level):
    typename = type(x).__name__
    if ' ' in typename:
        parts = typename.split()
        typename = '_'.join(parts)
    if hasattr(self, 'repr_' + typename):
        return getattr(self, 'repr_' + typename)(x, level)
    else:
        return self.repr_instance(x, level)

Repr.repr_list and truncation

# CPython: Lib/reprlib.py:108 Repr.repr_list
def repr_list(self, x, level):
    return self._repr_iterable(x, level, '[', ']', self.maxlist)

def _repr_iterable(self, x, level, left, right, maxitems, trail=''):
    n = len(x)
    if level <= 0 and n:
        s = '...'
    else:
        newlevel = level - 1
        repr1 = self.repr1
        pieces = [repr1(elem, newlevel) for elem in islice(x, maxitems)]
        if n > maxitems:
            pieces.append('...')
        s = ', '.join(pieces)
    return '%s%s%s' % (left, s, right)

maxlist (default 6) controls how many list items are shown before truncation.

aRepr singleton

aRepr = Repr() is the module-level instance used by the top-level repr() function (not builtins.repr). The interactive REPL uses it via sys.displayhook.

gopy notes

Status: not yet ported. reprlib is a pure-Python utility needed by pprint and the interactive loop. The recursive_repr decorator needs a goroutine-local set of uintptr (object addresses) rather than CPython's threading.local. The per-type repr_* dispatch is straightforward to port.