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[3.14] gh-132661: Document t-strings and templatelib (GH-135229) #136974

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7 changes: 6 additions & 1 deletion Doc/glossary.rst
Original file line number Diff line number Diff line change
Expand Up @@ -462,7 +462,7 @@ Glossary
core and with user code.

f-string
String literals prefixed with ``'f'`` or ``'F'`` are commonly called
String literals prefixed with ``f`` or ``F`` are commonly called
"f-strings" which is short for
:ref:`formatted string literals <f-strings>`. See also :pep:`498`.

Expand Down Expand Up @@ -1322,6 +1322,11 @@ Glossary

See also :term:`borrowed reference`.

t-string
String literals prefixed with ``t`` or ``T`` are commonly called
"t-strings" which is short for
:ref:`template string literals <t-strings>`.

text encoding
A string in Python is a sequence of Unicode code points (in range
``U+0000``--``U+10FFFF``). To store or transfer a string, it needs to be
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54 changes: 51 additions & 3 deletions Doc/library/ast.rst
Original file line number Diff line number Diff line change
Expand Up @@ -290,9 +290,9 @@ Literals
* ``conversion`` is an integer:

* -1: no formatting
* 115: ``!s`` string formatting
* 114: ``!r`` repr formatting
* 97: ``!a`` ascii formatting
* 115 (``ord('s')``): ``!s`` string formatting
* 114 (``ord('r')``): ``!r`` repr formatting
* 97 (``ord('a')``): ``!a`` ASCII formatting

* ``format_spec`` is a :class:`JoinedStr` node representing the formatting
of the value, or ``None`` if no format was specified. Both
Expand Down Expand Up @@ -326,6 +326,54 @@ Literals
Constant(value='.3')]))]))


.. class:: TemplateStr(values)

A t-string, comprising a series of :class:`Interpolation` and :class:`Constant`
nodes.

.. doctest::

>>> print(ast.dump(ast.parse('t"{name} finished {place:ordinal}"', mode='eval'), indent=4))
Expression(
body=TemplateStr(
values=[
Interpolation(
value=Name(id='name', ctx=Load()),
str='name',
conversion=-1),
Constant(value=' finished '),
Interpolation(
value=Name(id='place', ctx=Load()),
str='place',
conversion=-1,
format_spec=JoinedStr(
values=[
Constant(value='ordinal')]))]))

.. versionadded:: 3.14


.. class:: Interpolation(value, str, conversion, format_spec)

Node representing a single interpolation field in a t-string.

* ``value`` is any expression node (such as a literal, a variable, or a
function call).
* ``str`` is a constant containing the text of the interpolation expression.
* ``conversion`` is an integer:

* -1: no conversion
* 115: ``!s`` string conversion
* 114: ``!r`` repr conversion
* 97: ``!a`` ascii conversion

* ``format_spec`` is a :class:`JoinedStr` node representing the formatting
of the value, or ``None`` if no format was specified. Both
``conversion`` and ``format_spec`` can be set at the same time.

.. versionadded:: 3.14


.. class:: List(elts, ctx)
Tuple(elts, ctx)

Expand Down
42 changes: 42 additions & 0 deletions Doc/library/dis.rst
Original file line number Diff line number Diff line change
Expand Up @@ -1120,6 +1120,48 @@ iterations of the loop.
.. versionadded:: 3.12


.. opcode:: BUILD_TEMPLATE

Constructs a new :class:`~string.templatelib.Template` from a tuple
of strings and a tuple of interpolations and pushes the resulting instance
onto the stack::

interpolations = STACK.pop()
strings = STACK.pop()
STACK.append(_build_template(strings, interpolations))

.. versionadded:: 3.14


.. opcode:: BUILD_INTERPOLATION (format)

Constructs a new :class:`~string.templatelib.Interpolation` from a
value and its source expression and pushes the resulting instance onto the
stack.

If no conversion or format specification is present, ``format`` is set to
``2``.

If the low bit of ``format`` is set, it indicates that the interpolation
contains a format specification.

If ``format >> 2`` is non-zero, it indicates that the interpolation
contains a conversion. The value of ``format >> 2`` is the conversion type
(``0`` for no conversion, ``1`` for ``!s``, ``2`` for ``!r``, and
``3`` for ``!a``)::

conversion = format >> 2
if format & 1:
format_spec = STACK.pop()
else:
format_spec = None
expression = STACK.pop()
value = STACK.pop()
STACK.append(_build_interpolation(value, expression, conversion, format_spec))

.. versionadded:: 3.14


.. opcode:: BUILD_TUPLE (count)

Creates a tuple consuming *count* items from the stack, and pushes the
Expand Down
6 changes: 3 additions & 3 deletions Doc/library/stdtypes.rst
Original file line number Diff line number Diff line change
Expand Up @@ -2675,9 +2675,9 @@ For example:
lead to a number of common errors (such as failing to display tuples and
dictionaries correctly). Using the newer :ref:`formatted string literals
<f-strings>`, the :meth:`str.format` interface, or :ref:`template strings
<template-strings>` may help avoid these errors. Each of these
alternatives provides their own trade-offs and benefits of simplicity,
flexibility, and/or extensibility.
($-strings) <template-strings-pep292>` may help avoid these errors.
Each of these alternatives provides their own trade-offs and benefits of
simplicity, flexibility, and/or extensibility.

String objects have one unique built-in operation: the ``%`` operator (modulo).
This is also known as the string *formatting* or *interpolation* operator.
Expand Down
25 changes: 19 additions & 6 deletions Doc/library/string.rst
Original file line number Diff line number Diff line change
Expand Up @@ -198,8 +198,9 @@ Format String Syntax
The :meth:`str.format` method and the :class:`Formatter` class share the same
syntax for format strings (although in the case of :class:`Formatter`,
subclasses can define their own format string syntax). The syntax is
related to that of :ref:`formatted string literals <f-strings>`, but it is
less sophisticated and, in particular, does not support arbitrary expressions.
related to that of :ref:`formatted string literals <f-strings>` and
:ref:`template string literals <t-strings>`, but it is less sophisticated
and, in particular, does not support arbitrary expressions.

.. index::
single: {} (curly brackets); in string formatting
Expand Down Expand Up @@ -264,6 +265,8 @@ Some simple format string examples::
"Weight in tons {0.weight}" # 'weight' attribute of first positional arg
"Units destroyed: {players[0]}" # First element of keyword argument 'players'.

.. _formatstrings-conversion:

The *conversion* field causes a type coercion before formatting. Normally, the
job of formatting a value is done by the :meth:`~object.__format__` method of the value
itself. However, in some cases it is desirable to force a type to be formatted
Expand Down Expand Up @@ -306,7 +309,7 @@ Format Specification Mini-Language

"Format specifications" are used within replacement fields contained within a
format string to define how individual values are presented (see
:ref:`formatstrings` and :ref:`f-strings`).
:ref:`formatstrings`, :ref:`f-strings`, and :ref:`t-strings`).
They can also be passed directly to the built-in
:func:`format` function. Each formattable type may define how the format
specification is to be interpreted.
Expand Down Expand Up @@ -789,10 +792,20 @@ Nesting arguments and more complex examples::



.. _template-strings:
.. _template-strings-pep292:

Template strings
----------------
Template strings ($-strings)
----------------------------

.. note::

The feature described here was introduced in Python 2.4. It is unrelated
to, and should not be confused with, the newer
:ref:`template strings <template-strings>` and
:ref:`t-string literal syntax <t-strings>` introduced in Python 3.14.
T-string literals evaluate to instances of a different
:class:`~string.templatelib.Template` class, found in the
:mod:`string.templatelib` module.

Template strings provide simpler string substitutions as described in
:pep:`292`. A primary use case for template strings is for
Expand Down
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