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desugar Unravelled syntax assert ... With message Without a message for ... Without else With else with ... async def ... async for ... Without else With else async with ... Syntax to (potentially) unravel Keywords Expressions Statements Tokens Literals

README.md

desugar

Unravelling Python's syntactic sugar source code.

There are accompanying blog posts to go with all of the code in this repository.

Unravelled syntax

  1. obj.attr ➠ builtins.getattr(obj, "attr") (including object.__getattribute__())
  2. a + b ➠ operator.__add__(a, b)
  3. a - b ➠ operator.__sub__(a, b)
  4. a * b ➠ operator.__mul__(a, b)
  5. a @ b ➠ operator.__matmul__(a, b)
  6. a / b ➠ operator.__truediv__(a, b)
  7. a // b ➠ operator.__floordiv__(a, b)
  8. a % b ➠ operator.__mod__(a, b)
  9. a ** b ➠ operator.__pow__(a, b)
  10. a << b ➠ operator.__lshift__(a, b)
  11. a >> b ➠ operator.__rshift__(a, b)
  12. a & b ➠ operator.__and__(a, b)
  13. a ^ b ➠ operator.__xor__(a, b)
  14. a | b ➠ operator.__or__(a, b)
  15. a += b ➠ a = operator.__iadd__(a, b)
  16. a -= b ➠ a = operator.__isub__(a, b)
  17. a *= b ➠ a = operator.__imul__(a, b)
  18. a @= b ➠ a = operator.__imatmul__(a, b)
  19. a /= b ➠ a = operator.__itruediv__(a, b)
  20. a //= b ➠ a = operator.__ifloordiv__(a, b)
  21. a %= b ➠ a = operator.__imod__(a, b)
  22. a **= b ➠ a = operator.__ipow__(a, b)
  23. a <<= b ➠ a = operator.__ilshift__(a, b)
  24. a >>= b ➠ a = operator.__irshift__(a, b)
  25. a &= b ➠ a = operator.__iand__(a, b)
  26. a ^= b ➠ a = operator.__ixor__(a, b)
  27. a |= b ➠ a = operator.__ior__(a, b)
  28. ~ a ➠ operator.__invert__(a)
  29. - a ➠ operator.__neg__(a)
  30. + a ➠ operator.__pos__(a)
  31. a == b ➠ operator.__eq__(a, b) (including object.__eq__())
  32. a != b ➠ operator.__ne__(a, b) (including object.__ne__())
  33. a < b ➠ operator.__lt__(a, b)
  34. a <= b ➠ operator.__le__(a, b)
  35. a > b ➠ operator.__gt__(a, b)
  36. a >= b ➠ operator.__ge__(a, b)
  37. a is b ➠ operator.is_(a, b)
  38. a is not b ➠ operator.is_not(a, b)
  39. not a ➠ operator.not_(a)
  40. a in b ➠ operator.__contains__(b, a)
  41. a not in b ➠ operator.not_(operator.__contains__(b, a))
  42. a or b ➠ _temp if (_temp := a) else b
  43. a and b ➠ _temp if not (_temp := a) else b
  44. import a.b ➠ a = __import__('a.b', globals(), locals())
  45. import a.b as c ➠ c = __import__('a', globals(), locals(), ['b'], 0).b
  46. from .a import b ➠ b = __import__('a', globals(), locals(), ['b'], 1).b
  47. from .a import b as c ➠ c = __import__('a', globals(), locals(), ['b'], 1).b
  48. assert ... ➠ see below (post)
  49. for ... ➠ see below (including builtins.iter() and builtins.next())
  50. pass ➠ "pass"
  51. with ... ➠ see below (post)
  52. async def ... ➠ see below (post)
  53. await ... ➠ desugar.builtins._await(...)
  54. async for ➠ see below (including builtins.aiter() and builtins.anext())
  55. async with ➠ see below (post)
  56. [c for b in a] ➠ list(c for b in a)
  57. {c for b in a} ➠ set(c for b in a)
  58. {c: d for b in a} ➠ dict((c, d) for b in a)
  59. [a, b] ➠ list((a, b)) (includes iterable unpacking)
  60. {a, b} ➠ set((a, b)) (includes iterable unpacking)
  61. (a, b)) ➠ (lambda *args: args)(a, b) (includes iterable unpacking)
  62. {a: b, c: d}) ➠ dict(((a, b), (c, d))) (include dictionary unpacking)

assert ...

With message

assert a, b

➠

if __debug__:
    if not a:
        raise AssertionError(b)

Without a message

assert a

➠

if __debug__:
    if not a:
        raise AssertionError

for ...

Without else

for a in b:
    c

➠

_iter = iter(b)
while True:
    try:
        a = next(_iter)
    except StopIteration:
        break
    else:
        c
del _iter

With else

for a in b:
    c
else:
    d

➠

_iter = iter(b)
_looping = True
while _looping:
    try:
        a = next(_iter)
    except StopIteration:
        _looping = False
        continue
    else:
        c
else:
    d
del _iter, _looping

with ...

with a as b:
    c

➠

_enter = type(a).__enter__
_exit = type(a).__exit__
b = _enter(a)

try:
    c
except:
    if not _exit(a, *sys.exc_info()):
        raise
else:
    _exit(a, None, None, None)

async def ...

async def spam():
    ...

➠

@types.coroutine
def spam():
    ...

async for ...

Without else

async for a in b:
    c

➠

_iter = aiter(b)
while True:
    try:
        a = await anext(_iter)
    except StopAsyncIteration:
        break
    else:
        c
del _iter

With else

async for a in b:
    c
else:
    d

➠

_iter = aiter(b)
_looping = True
while _looping:
    try:
        a = await anext(_iter)
    except StopAsyncIteration:
        _looping = False
        continue
    else:
        c
else:
    d
del _iter, _looping

async with ...

async with a as b:
    c

➠

_enter = type(a).__aenter__
_exit = type(a).__aexit__
b = await _enter(a)

try:
    c
except:
    if not await _exit(a, *sys.exc_info()):
        raise
else:
    await _exit(a, None, None, None)

Syntax to (potentially) unravel

Keywords

Taken from the keyword module.

Expressions

  1. yield
  2. lambda

Statements

  1. break

  2. continue

  3. if/elif/else

  4. while/else

  5. def

  6. class ~

  7. try/except/else/finally

  8. global

  9. nonlocal

  10. del

  11. raise/from

  12. return

Tokens

Taken from the token module.

  1. =

  2. :=

  3. [] for subscriptions (get, set, del), : for slicing *

  4. () for generator expressions (and why they can't be unravelled)

  5. () for calls

  6. @ for decorators *

  7. ,

  8. ; *

  9. ... *

Literals

The list below ignores literals which are represented via syntax above. For instance, lists are ignored as they are represented by [] tokens.

  1. None
  2. False
  3. True
  4. Bytes (b, r)
  5. Strings (u, f, r; single line, multi-line) *
  6. Integers (base-10, b, o, x)
  7. Floats (point, e)
  8. Complex/imaginary numbers

About

Unravelling Python source code

pypi.org/project/desugar/

Resources

Readme

License

MIT License

Releases

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