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gh-151099: Better repr output for template strings. #151104

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654ff70
gh-151099: Better repr output for template strings.
doerwalter Jun 8, 2026
16f8ca3
Don't hardcode the class name in case of a cycle.
doerwalter Jun 10, 2026
8ab352e
Update pprint implementation to mirror the new repr format for string…
doerwalter Jun 17, 2026
ae95a48
Omit conversion and format_spec in t-string repr and pprint output if…
doerwalter Jun 25, 2026
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31 changes: 15 additions & 16 deletions Lib/pprint.py
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Original file line number Diff line number Diff line change
Expand Up @@ -737,18 +737,13 @@ def _pprint_user_string(self, object, stream, indent, allowance, context, level)

def _pprint_template(self, object, stream, indent, allowance, context, level):
cls_name = object.__class__.__name__
if self._expand:
indent += self._indent_per_level
else:
indent += len(cls_name) + 1

items = (
("strings", object.strings),
("interpolations", object.interpolations),
)
if not self._expand:
indent += len(cls_name)

stream.write(self._format_block_start(cls_name + "(", indent))
self._format_namespace_items(
items, stream, indent, allowance, context, level
self._format_items(
object, stream, indent, allowance, context, level
)
stream.write(
self._format_block_end(")", indent - self._indent_per_level)
Expand All @@ -758,13 +753,15 @@ def _pprint_interpolation(self, object, stream, indent, allowance, context, leve
cls_name = object.__class__.__name__
if self._expand:
indent += self._indent_per_level
stream.write(self._format_block_start(cls_name + "(", indent))
items = (
("value", object.value),
("expression", object.expression),
("conversion", object.conversion),
("format_spec", object.format_spec),
)
stream.write(self._format_block_start(cls_name + "(", indent))
if object.conversion is not None or object.format_spec:
items += (("conversion", object.conversion),)
if object.format_spec:
items += (("format_spec", object.format_spec),)
self._format_namespace_items(
items, stream, indent, allowance, context, level
)
Expand All @@ -773,13 +770,15 @@ def _pprint_interpolation(self, object, stream, indent, allowance, context, leve
)
else:
indent += len(cls_name)
stream.write(cls_name + "(")
items = (
object.value,
object.expression,
object.conversion,
object.format_spec,
)
stream.write(cls_name + "(")
if object.conversion is not None or object.format_spec:
items += (object.conversion,)
if object.format_spec:
items += (object.format_spec,)
self._format_items(
items, stream, indent, allowance, context, level
)
Expand Down
159 changes: 114 additions & 45 deletions Lib/test/test_pprint.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1517,56 +1517,129 @@ def test_user_string(self):

def test_template(self):
d = t""
self.assertEqual(pprint.pformat(d),
"Template(strings=('',), interpolations=())")
self.assertEqual(pprint.pformat(d), "Template()")
self.assertEqual(pprint.pformat(d), repr(d))
self.assertEqual(pprint.pformat(d, width=1),
"""\
Template(strings=('',),
interpolations=())""")
self.assertEqual(pprint.pformat(d, width=1), "Template()")
name = "World"
d = t"Hello {name}"
self.assertEqual(pprint.pformat(d),
"""\
Template(strings=('Hello ', ''),
interpolations=(Interpolation('World', 'name', None, ''),))""")
Template('Hello ', Interpolation('World', 'name'))""")
d = t"Hello {name!r}"
self.assertEqual(pprint.pformat(d),
"""\
Template('Hello ', Interpolation('World', 'name', 'r'))""")
d = t"Hello {name:0}"
self.assertEqual(pprint.pformat(d),
"""\
Template('Hello ', Interpolation('World', 'name', None, '0'))""")
d = t"Hello {name!r:0}"
self.assertEqual(pprint.pformat(d),
"""\
Template('Hello ', Interpolation('World', 'name', 'r', '0'))""")
d = t"Hello {name}"
self.assertEqual(pprint.pformat(d, width=10),
"""\
Template('Hello ',
Interpolation('World',
'name'))""")
d = t"Hello {name!r}"
self.assertEqual(pprint.pformat(d, width=10),
"""\
Template('Hello ',
Interpolation('World',
'name',
'r'))""")
d = t"Hello {name:0}"
self.assertEqual(pprint.pformat(d, width=10),
"""\
Template('Hello ',
Interpolation('World',
'name',
None,
'0'))""")
d = t"Hello {name!r:0}"
self.assertEqual(pprint.pformat(d, width=10),
"""\
Template('Hello ',
Interpolation('World',
'name',
'r',
'0'))""")
ver = {3.13: False, 3.14: True}
d = t"Hello { {"name": "Python", "version": ver}!s:z}!"
self.assertEqual(pprint.pformat(d, width=1),
"""\
Template(strings=('Hello ',
'!'),
interpolations=(Interpolation({'name': 'Python',
'version': {3.13: False,
3.14: True}},
' '
'{"name": '
'"Python", '
'"version": '
'ver}',
's',
'z'),))""")
Template('Hello ',
Interpolation({'name': 'Python',
'version': {3.13: False,
3.14: True}},
' '
'{"name": '
'"Python", '
'"version": '
'ver}',
's',
'z'),
'!')""")

def test_expand_template(self):
d = t""
self.assertEqual(
pprint.pformat(d, expand=True),
"Template(strings=('',), interpolations=())",
"Template()",
)
name = "World"
d = t"Hello {name}"
self.assertEqual(
pprint.pformat(d, width=40, indent=4, expand=True),
pprint.pformat(d, width=30, indent=4, expand=True),
"""\
Template(
strings=('Hello ', ''),
interpolations=(
Interpolation(
value='World',
expression='name',
conversion=None,
format_spec='',
),
'Hello ',
Interpolation(
value='World',
expression='name',
),
)""",
)
d = t"Hello {name!r}"
self.assertEqual(
pprint.pformat(d, width=30, indent=4, expand=True),
"""\
Template(
'Hello ',
Interpolation(
value='World',
expression='name',
conversion='r',
),
)""",
)
d = t"Hello {name:0}"
self.assertEqual(
pprint.pformat(d, width=30, indent=4, expand=True),
"""\
Template(
'Hello ',
Interpolation(
value='World',
expression='name',
conversion=None,
format_spec='0',
),
)""",
)
d = t"Hello {name!r:0}"
self.assertEqual(
pprint.pformat(d, width=30, indent=4, expand=True),
"""\
Template(
'Hello ',
Interpolation(
value='World',
expression='name',
conversion='r',
format_spec='0',
),
)""",
)
Expand All @@ -1576,22 +1649,18 @@ def test_expand_template(self):
pprint.pformat(d, width=40, indent=4, expand=True),
"""\
Template(
strings=('Hello ', '!'),
interpolations=(
Interpolation(
value={
'name': 'Python',
'version': {
3.13: False,
3.14: True,
},
},
expression=' {"name": "Python", '
'"version": ver}',
conversion='s',
format_spec='z',
),
'Hello ',
Interpolation(
value={
'name': 'Python',
'version': {3.13: False, 3.14: True},
},
expression=' {"name": "Python", '
'"version": ver}',
conversion='s',
format_spec='z',
),
'!',
)""",
)

Expand Down
27 changes: 27 additions & 0 deletions Lib/test/test_string/test_templatelib.py
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Original file line number Diff line number Diff line change
Expand Up @@ -101,6 +101,33 @@ def test_template_values(self):
t = t'Hello, {name}, {age} from {country}'
self.assertEqual(t.values, ("Lys", 0, "GR"))

def test_repr(self):
self.assertEqual(repr(t''), 'Template()')
self.assertEqual(repr(t'foo'), "Template('foo')")

# Test various combination for present/absent conversion and format_spec
x = 42
self.assertEqual(
repr(t'{x}'),
"Template(Interpolation(42, 'x'))")
self.assertEqual(
repr(t'{x!r}'),
"Template(Interpolation(42, 'x', 'r'))")
self.assertEqual(
repr(t'{x:02}'),
"Template(Interpolation(42, 'x', None, '02'))")
self.assertEqual(
repr(t'a{x!r:02}b'),
"Template('a', Interpolation(42, 'x', 'r', '02'), 'b')")

# Test a "recursive" template
x = []
t = t'a{x}b'
x.append(t)
self.assertEqual(
repr(t),
"Template('a', Interpolation([Template(...)], 'x'), 'b')")

def test_pickle_template(self):
user = 'test'
for template in (
Expand Down
2 changes: 2 additions & 0 deletions Misc/NEWS.d/next/Library/2026-06-08-20-38-28.gh-issue-151099.6Opls1.rst
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Original file line number Diff line number Diff line change
@@ -0,0 +1,2 @@
Change :func:`repr` output of :class:`string.templatelib.Template` objects
to list the parts of the template in their original source order.
28 changes: 25 additions & 3 deletions Objects/interpolationobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -112,9 +112,31 @@ static PyObject *
interpolation_repr(PyObject *op)
{
interpolationobject *self = interpolationobject_CAST(op);
return PyUnicode_FromFormat("%s(%R, %R, %R, %R)",
_PyType_Name(Py_TYPE(self)), self->value, self->expression,
self->conversion, self->format_spec);

/* Only emit trailing arguments that differ from their default values
(conversion=None and format_spec=""). We never use keyword arguments, so
if 'format_spec' is non-default, 'conversion' has to be emitted too even
when it still has its default value. */
int show_format_spec = PyUnicode_GET_LENGTH(self->format_spec) > 0;
int show_conversion = show_format_spec || self->conversion != Py_None;

if (show_format_spec) {
return PyUnicode_FromFormat("%s(%R, %R, %R, %R)",
_PyType_Name(Py_TYPE(self)),
self->value, self->expression,
self->conversion, self->format_spec);
}
else if (show_conversion) {
return PyUnicode_FromFormat("%s(%R, %R, %R)",
_PyType_Name(Py_TYPE(self)),
self->value, self->expression,
self->conversion);
}
else {
return PyUnicode_FromFormat("%s(%R, %R)",
_PyType_Name(Py_TYPE(self)),
self->value, self->expression);
}
}

static PyMemberDef interpolation_members[] = {
Expand Down
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