py: Add PEP 750 template strings support #17557

koxudaxi · 2025-06-24T19:32:57Z

Summary

Implements PEP 750 template strings for MicroPython.

Started in discussion #17497. Template strings (t-strings) are new in Python 3.14 - they return Template objects instead of strings, so you can access the literal parts and expressions separately.

Changes:

t-string parsing in lexer/parser
Template and Interpolation objects
string.templatelib module
Conditional build with MICROPY_PY_TSTRINGS

Usage:

t = t"Hello {name}!"
str(t)  # "Hello World!"
t.args[1].expression  # "name" 
t.args[1].value  # "World"

Testing

Tested on unix port with both MICROPY_PY_TSTRINGS enabled and disabled.

Test coverage:

Basic template string functionality
Error handling and edge cases
Import system integration
Nested expression parsing

All existing tests continue to pass. New tests added in tests/basics/string_template*.py.

Ports tested: Unix (other ports need testing)

Trade-offs and Alternatives

Adds ~240 bytes when enabled on unix port. When disabled, no impact.

Worth it because:

Part of Python 3.14 standard
Optional feature (MICROPY_PY_TSTRINGS)
Useful for template processing

Config: Enabled by default when MICROPY_CONFIG_ROM_LEVEL >= EXTRA_FEATURES.
Needs MICROPY_PY_FSTRINGS=1.

To disable: make CFLAGS_EXTRA=-DMICROPY_PY_TSTRINGS=0

Implements template strings (t-strings) as specified in PEP 750 for Python 3.14. Template strings are a generalization of f-strings that return Template objects instead of strings, enabling safer string processing and custom formatting. Key changes: - Add lexer/parser support for t"..." and rt"..." literals - Implement Template and Interpolation object types - Create string.templatelib module - Add comprehensive test suite and documentation This feature is opt-in via MICROPY_PY_TSTRINGS configuration and has zero impact when disabled. It requires MICROPY_PY_FSTRINGS to be enabled. Signed-off-by: Koudai Aono <[email protected]>

WebReflection · 2025-06-24T19:54:35Z

for what is worth it, we'd love to have this available at least for the PyScript WASM variant as this unlocks tons of UI related use cases we'd like to deliver to our users.

/cc @dpgeorge @ntoll

Signed-off-by: Koudai Aono <[email protected]>

codecov · 2025-06-25T02:23:46Z

Codecov Report

Attention: Patch coverage is 37.57225% with 324 lines in your changes missing coverage. Please review.

Project coverage is 97.16%. Comparing base (e57aa7e) to head (16a0f73).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
py/modtstring.c	12.29%	214 Missing ⚠️
py/parse.c	70.89%	39 Missing ⚠️
py/objinterpolation.c	28.20%	28 Missing ⚠️
py/tstring_expr_parser.c	55.00%	18 Missing ⚠️
py/modstring.c	0.00%	13 Missing ⚠️
py/lexer.c	75.51%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #17557      +/-   ##
==========================================
- Coverage   98.57%   97.16%   -1.41%     
==========================================
  Files         169      173       +4     
  Lines       21968    22473     +505     
==========================================
+ Hits        21654    21835     +181     
- Misses        314      638     +324

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

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…are disabled Signed-off-by: Koudai Aono <[email protected]>

Signed-off-by: Koudai Aono <[email protected]>

github-actions · 2025-06-25T04:56:57Z

Code size report:

   bare-arm:   +28 +0.049% 
minimal x86:   +58 +0.031% [incl +32(data)]
   unix x64: +10056 +1.176% standard[incl +608(data) +32(bss)]
      stm32: +4884 +1.245% PYBV10[incl +4(bss)]
     mimxrt: +4872 +1.306% TEENSY40
        rp2: +4600 +0.501% RPI_PICO_W
       samd: +5060 +1.883% ADAFRUIT_ITSYBITSY_M4_EXPRESS[incl +8(bss)]
  qemu rv32: +5711 +1.260% VIRT_RV32[incl +1(bss)]

dpgeorge

Thanks for the contribution! This will be nice to have for the webassembly port.

I didn't do a review yet, but there will need to be tests to get full coverage of the new code.

dpgeorge · 2025-06-25T05:59:13Z

docs/library/btree.rst

@@ -130,31 +130,50 @@ Methods
   to get access to all keys in order.

 .. method:: btree.keys([start_key, [end_key, [flags]]])
-            btree.values([start_key, [end_key, [flags]]])


This is an unrelated change, so please put it in a separate PR.

(This PR itself will be big enough, so let's aim to make it as easy as possible to review.)

dpgeorge · 2025-06-25T06:01:29Z

py/modbuiltins.c

@@ -525,6 +525,326 @@ static mp_obj_t mp_builtin_sum(size_t n_args, const mp_obj_t *args) {
 }
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(mp_builtin_sum_obj, 1, 2, mp_builtin_sum);

+#if MICROPY_PY_TSTRINGS


I think this new code should go in its own, separate file.

koxudaxi · 2025-06-25T06:33:07Z

@dpgeorge Thank you for the feedback and for taking time to look at this! I'm glad this will be useful for the webassembly port.

I'll add more tests to ensure full coverage when I find time.

Signed-off-by: Koudai Aono <[email protected]>

…modtstring.c Signed-off-by: Koudai Aono <[email protected]>

ntoll · 2025-06-25T08:59:43Z

@koxudaxi slightly off topic - but I notice you'll be at EuroPython in Prague, as will I. We should look out for each other and have a coffee or lunch together! 🇪🇺 🐍

…s for template strings Signed-off-by: Koudai Aono <[email protected]>

…ion and concatenation support Signed-off-by: Koudai Aono <[email protected]>

…ings Signed-off-by: Koudai Aono <[email protected]>

koxudaxi added 2 commits June 25, 2025 05:12

py: Cast f-string arguments to unichar in lexer

190eb98

Signed-off-by: Koudai Aono <[email protected]>

py: ignore ruff check for PEP750 tests

05503a2

Signed-off-by: Koudai Aono <[email protected]>

koxudaxi changed the title ~~py: Add PEP 750 template strings support.~~ py: Add PEP 750 template strings support Jun 24, 2025

koxudaxi added 9 commits June 25, 2025 05:38

doc: Update btree methods documentation for key sub-range iteration

1588ee8

Signed-off-by: Koudai Aono <[email protected]>

py: Enable PEP 750 template strings support in configuration

01e5ef5

Signed-off-by: Koudai Aono <[email protected]>

py: Add support for PEP 750 template strings in test runner

7dfd85d

Signed-off-by: Koudai Aono <[email protected]>

py: Add documentation for t-string nesting behavior in MicroPython

e97faa7

Signed-off-by: Koudai Aono <[email protected]>

py: Exclude additional PEP 750 template string tests from Ruff checks

9763c65

Signed-off-by: Koudai Aono <[email protected]>

py: Fix missing newline at end of file in t-string nesting message

bcfcaf5

Signed-off-by: Koudai Aono <[email protected]>

py: fix format

ee6a1e2

Signed-off-by: Koudai Aono <[email protected]>

py: fix tests

5b8cbcd

Signed-off-by: Koudai Aono <[email protected]>

py: ignore ruff format check

69e0b46

Signed-off-by: Koudai Aono <[email protected]>

koxudaxi added 3 commits June 25, 2025 13:06

py: add stub implementations for interpolation when template strings …

80b5f82

…are disabled Signed-off-by: Koudai Aono <[email protected]>

py: refactor f-string character detection function

445e50e

Signed-off-by: Koudai Aono <[email protected]>

py: add objinterpolation and tstring_expr_parser to build configuration

0279def

Signed-off-by: Koudai Aono <[email protected]>

dpgeorge added the py-core Relates to py/ directory in source label Jun 25, 2025

dpgeorge reviewed Jun 25, 2025

View reviewed changes

koxudaxi added 3 commits June 25, 2025 16:13

doc: revert documentation for btree methods and their parameters

4fdc854

Signed-off-by: Koudai Aono <[email protected]>

py: create modstrings.c

a0ddc8d

Signed-off-by: Koudai Aono <[email protected]>

py: add forward declarations for template and interpolation types in …

0447560

…modtstring.c Signed-off-by: Koudai Aono <[email protected]>

koxudaxi added 3 commits June 25, 2025 18:05

py: update interpolation function declaration and include dependencie…

f9aaf49

…s for template strings Signed-off-by: Koudai Aono <[email protected]>

py: enhance template string functionality with format spec interpolat…

ceb55b2

…ion and concatenation support Signed-off-by: Koudai Aono <[email protected]>

py: add tests for implicit concatenation restrictions in template str…

16a0f73

…ings Signed-off-by: Koudai Aono <[email protected]>

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py: Add PEP 750 template strings support #17557

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koxudaxi commented Jun 24, 2025

Summary

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