gh-151099: Better repr output for template strings.

[doerwalter]

This changes the repr ouput for template strings to list the template parts in their original order (which is the same order in which those parts can be passed to the Template constructor to recreate the Template object).

This has been discussed here: https://discuss.python.org/t/repr-output-of-t-strings/107653/8

The issue is here: #151099

• Issue: Better repr for string.templatelib.Template. #151099

[loic-simon]

We should update pprint functions output accordingly (introduced here, I can lend a hand if needed!)

[loic-simon]

should we use _PyType_Name(Py_TYPE(self)) instead of hardcoding Template here?

[doerwalter]

I've updated the patch to do that.

And I also changed the call to Py_ReprEnter/Py_ReprLeave to pass op instead of self to avoid compiler warnings.

[doerwalter]

I tried updating pprint.PrettyPrinter._pprint_template() like this

--- a/Lib/pprint.py
+++ b/Lib/pprint.py
@@ -742,13 +742,9 @@ def _pprint_template(self, object, stream, indent, allowance, context, level):
         else:
             indent += len(cls_name) + 1

-        items = (
-            ("strings", object.strings),
-            ("interpolations", object.interpolations),
-        )
         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
         )

but somehow this gives me an extra level of indentation

>>> import pprint
>>> print(pprint.pformat(t'Hello {'world'}', width=40, indent=4, expand=True))
Template(
        'Hello ',
        Interpolation(
            value='world',
            expression="'world'",
            conversion=None,
            format_spec='',
        ),
)
>>> print(pprint.pformat(t'Hello {'world'}', width=40, indent=4, expand=False))
Template(   'Hello ',
             Interpolation(   'world',
                              "'world'",
                              None,
                              ''))

What am I doing wrong?

[loic-simon]

Hm, I believe that's the indented output! If you try

>>> print(pprint.pformat(['Hello', 'foo'*10], width=40, indent=4, expand=False))
[   'Hello',
    'foofoofoofoofoofoofoofoofoofoo']

the extra indentation is the same, even if I would not have expected it either 😅

[doerwalter]

The expand=False output is indeed unexpected, but the expand=True output is wrong, since the first indentation level is 8 spaces and the second level is 4.

[loic-simon]

Okay, I think it's because we don't need the indent += self._indent_per_level with self.format_items, otherwise we ident twice:

--- a/Lib/pprint.py
+++ b/Lib/pprint.py
@@ -739,7 +739,5 @@ def _pprint_template(self, object, stream, indent, allowance, context, level):
         cls_name = object.__class__.__name__
-        if self._expand:
-            indent += self._indent_per_level
-        else:
+        if not self._expand:
             indent += len(cls_name) + 1

That still doesn't look super nice, but not worse than today!