Merge pull request #4133 from HypothesisWorks/DRMacIver/better-record…

…-printing

Add better support for pretty-printing record types

hypothesis-python/RELEASE.rst

@@ -0,0 +1,4 @@
+RELEASE_TYPE: minor
+
+This improves the formatting of dataclasses and attrs classes when printing
+falsifying examples.

hypothesis-python/src/hypothesis/vendor/pretty.py

@@ -214,6 +214,24 @@ def pretty(self, obj):
  meth = cls._repr_pretty_
  if callable(meth):
  return meth(obj, self, cycle)
+ if hasattr(cls, "__attrs_attrs__"):
+ return pprint_fields(
+ obj,
+ self,
+ cycle,
+ [at.name for at in cls.__attrs_attrs__ if at.init],
+ )
+ if hasattr(cls, "__dataclass_fields__"):
+ return pprint_fields(
+ obj,
+ self,
+ cycle,
+ [
+ k
+ for k, v in cls.__dataclass_fields__.items()
+ if v.init
+ ],
+ )
  # Now check for object-specific printers which show how this
  # object was constructed (a Hypothesis special feature).
  printers = self.known_object_printers[IDKey(obj)]
@@ -714,6 +732,20 @@ def _repr_pprint(obj, p, cycle):
  p.text(output_line)
 
 
+def pprint_fields(obj, p, cycle, fields):
+ name = obj.__class__.__name__
+ if cycle:
+ return p.text(f"{name}(...)")
+ with p.group(1, name + "(", ")"):
+ for idx, field in enumerate(fields):
+ if idx:
+ p.text(",")
+ p.breakable()
+ p.text(field)
+ p.text("=")
+ p.pretty(getattr(obj, field))
+
+
 def _function_pprint(obj, p, cycle):
  """Base pprint for all functions and builtin functions."""
  from hypothesis.internal.reflection import get_pretty_function_description

hypothesis-python/tests/cover/test_pretty.py

@@ -49,11 +49,14 @@
 
 import re
 import struct
+import sys
 import warnings
 from collections import Counter, OrderedDict, defaultdict, deque
+from dataclasses import dataclass, field
 from enum import Enum, Flag
 from functools import partial
 
+import attrs
 import pytest
 
 from hypothesis import given, strategies as st
@@ -758,3 +761,118 @@ def test_pprint_extremely_large_integers():
  got = p.getvalue()
  assert got == f"{x:#_x}" # hexadecimal with underscores
  assert eval(got) == x
+
+
+class ReprDetector:
+ def _repr_pretty_(self, p, cycle):
+ """Exercise the IPython callback interface."""
+ p.text("GOOD")
+
+ def __repr__(self):
+ return "BAD"
+
+
+@dataclass
+class SomeDataClass:
+ x: object
+
+
+def test_pretty_prints_data_classes():
+ assert pretty.pretty(SomeDataClass(ReprDetector())) == "SomeDataClass(x=GOOD)"
+
+
+@attrs.define
+class SomeAttrsClass:
+ x: ReprDetector
+
+
+@pytest.mark.skipif(sys.version_info[:2] >= (3, 14), reason="FIXME-py314")
+def test_pretty_prints_attrs_classes():
+ assert pretty.pretty(SomeAttrsClass(ReprDetector())) == "SomeAttrsClass(x=GOOD)"
+
+
+@attrs.define
+class SomeAttrsClassWithCustomPretty:
+ def _repr_pretty_(self, p, cycle):
+ """Exercise the IPython callback interface."""
+ p.text("I am a banana")
+
+
+def test_custom_pretty_print_method_overrides_field_printing():
+ assert pretty.pretty(SomeAttrsClassWithCustomPretty()) == "I am a banana"
+
+
+@attrs.define
+class SomeAttrsClassWithLotsOfFields:
+ a: int
+ b: int
+ c: int
+ d: int
+ e: int
+ f: int
+ g: int
+ h: int
+ i: int
+ j: int
+ k: int
+ l: int
+ m: int
+ n: int
+ o: int
+ p: int
+ q: int
+ r: int
+ s: int
+
+
+@pytest.mark.skipif(sys.version_info[:2] >= (3, 14), reason="FIXME-py314")
+def test_will_line_break_between_fields():
+ obj = SomeAttrsClassWithLotsOfFields(
+ **{
+ at.name: 12345678900000000000000001
+ for at in SomeAttrsClassWithLotsOfFields.__attrs_attrs__
+ }
+ )
+ assert "\n" in pretty.pretty(obj)
+
+
+@attrs.define
+class SomeDataClassWithNoFields: ...
+
+
+def test_prints_empty_dataclass_correctly():
+ assert pretty.pretty(SomeDataClassWithNoFields()) == "SomeDataClassWithNoFields()"
+
+
+def test_handles_cycles_in_dataclass():
+ x = SomeDataClass(x=1)
+ x.x = x
+
+ assert pretty.pretty(x) == "SomeDataClass(x=SomeDataClass(...))"
+
+
+@dataclass
+class DataClassWithNoInitField:
+ x: int
+ y: int = field(init=False)
+
+
+def test_does_not_include_no_init_fields_in_dataclass_printing():
+ record = DataClassWithNoInitField(x=1)
+ assert pretty.pretty(record) == "DataClassWithNoInitField(x=1)"
+ record.y = 1
+ assert pretty.pretty(record) == "DataClassWithNoInitField(x=1)"
+
+
+@attrs.define
+class AttrsClassWithNoInitField:
+ x: int
+ y: int = attrs.field(init=False)
+
+
+@pytest.mark.skipif(sys.version_info[:2] >= (3, 14), reason="FIXME-py314")
+def test_does_not_include_no_init_fields_in_attrs_printing():
+ record = AttrsClassWithNoInitField(x=1)
+ assert pretty.pretty(record) == "AttrsClassWithNoInitField(x=1)"
+ record.y = 1
+ assert pretty.pretty(record) == "AttrsClassWithNoInitField(x=1)"