reprlib (used by pytest) infers builtin types based on class __name__

[jpivarski]

Bug report

Bug description:

Code like the following:

import reprlib

class array:
    def __repr__(self):
        return "not array.array!"

reprlib.repr(array())

raises

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/jpivarski/mambaforge/lib/python3.10/reprlib.py", line 52, in repr
    return self.repr1(x, self.maxlevel)
  File "/home/jpivarski/mambaforge/lib/python3.10/reprlib.py", line 60, in repr1
    return getattr(self, 'repr_' + typename)(x, level)
  File "/home/jpivarski/mambaforge/lib/python3.10/reprlib.py", line 86, in repr_array
    header = "array('%s', [" % x.typecode
AttributeError: 'array' object has no attribute 'typecode'

because reprlib uses type(x).__name__ to infer that x has type array.array, rather than my user-defined class:

cpython/Lib/reprlib.py

Lines 62 to 70 in cf34b77

	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)

Perhaps there's good reason to check the __name__ string instead of isinstance(x, array.array), to avoid unnecessarily importing the array module for start-up time or for minimizing clutter in the sys.modules. However, this test should check both the __name__ string and the __module__ string.

This affects any user-defined classes with the following names:

• tuple
• list
• array
• set
• frozenset
• deque
• dict
• str
• int
• instance

Some of these, admittedly, would be bad names for user-defined classes, but others are more reasonable, such as array and deque.¹

Since these methods are publicly available on class reprlib.Repr, the method names can't change, but the lookup could be replaced using a dict like

class Repr:
    _lookup = {
        ("builtins", "tuple"): repr_tuple,
        ("builtins", "list"): repr_list,
        ("array", "array"): repr_array,
        ("builtins", "set"): repr_set,
        ("builtins", "frozenset"): repr_frozenset,
        ("collections", "deque"): repr_deque,
        ("builtins", "dict"): repr_dict,
        ("builtins", "str"): repr_str,
        ("builtins", "int"): repr_int,
    }

---

I encountered this in pytest. My error output contained

x          = <[ValueError('the truth value of an array whose length is not 1 is ambiguous; use ak.any() or ak.all()') raised in repr()] array object at 0x779b54763700>
y          = array([1, 2, 3])

or

x          = <[AttributeError("'array' object has no attribute 'typecode'") raised in repr()] array object at 0x728278bacd60>
y          = array([1, 2, 3])

for reasons that had nothing to do with the actual error, and the array.__repr__ code itself is error-free. (pytest overrides reprlib to provide a SafeRepr.)

Thanks!

CPython versions tested on:

3.10

Operating systems tested on:

Linux

Linked PRs

• gh-113570: reprlib.repr does not use builtin __repr__ for reshadowed builtins #113577
• [3.13] gh-113570: reprlib.repr does not use builtin __repr__ for reshadowed builtins (GH-113577) #125654
• [3.12] gh-113570: reprlib.repr does not use builtin __repr__ for reshadowed builtins (GH-113577) #125655

Footnotes

1. In my case, I want the ragged library to provide a ragged.array because it reads like English that way. I also don't want to change the __name__ of my class to differ from its actual name. In particular, the Array API specification uses "array" as a type name. ↩

[jpivarski]

This is what I'm using as a workaround for pytest, in my conftest.py file:

import reprlib
import pytest
import my_own_library

@pytest.fixture(scope="session", autouse=True)
def _patch_reprlib():
    if not hasattr(reprlib.Repr, "repr1_original"):

        def repr1(self, x, level):
            if isinstance(x, ragged.array):
                return self.repr_instance(x, level)
            return self.repr1_original(x, level)

        reprlib.Repr.repr1_original = reprlib.Repr.repr1
        reprlib.Repr.repr1 = repr1