Unravelling Python's syntactic sugar source code.
There are accompanying blog posts to go with all of the code in this repository.
obj.attr➠builtins.getattr(obj, "attr")(includingobject.__getattribute__())a + b➠operator.__add__(a, b)a - b➠operator.__sub__(a, b)a * b➠operator.__mul__(a, b)a @ b➠operator.__matmul__(a, b)a / b➠operator.__truediv__(a, b)a // b➠operator.__floordiv__(a, b)a % b➠operator.__mod__(a, b)a ** b➠operator.__pow__(a, b)a << b➠operator.__lshift__(a, b)a >> b➠operator.__rshift__(a, b)a & b➠operator.__and__(a, b)a ^ b➠operator.__xor__(a, b)a | b➠operator.__or__(a, b)a += b➠a = operator.__iadd__(a, b)a -= b➠a = operator.__isub__(a, b)a *= b➠a = operator.__imul__(a, b)a @= b➠a = operator.__imatmul__(a, b)a /= b➠a = operator.__itruediv__(a, b)a //= b➠a = operator.__ifloordiv__(a, b)a %= b➠a = operator.__imod__(a, b)a **= b➠a = operator.__ipow__(a, b)a <<= b➠a = operator.__ilshift__(a, b)a >>= b➠a = operator.__irshift__(a, b)a &= b➠a = operator.__iand__(a, b)a ^= b➠a = operator.__ixor__(a, b)a |= b➠a = operator.__ior__(a, b)~ a➠operator.__invert__(a)- a➠operator.__neg__(a)+ a➠operator.__pos__(a)a == b➠operator.__eq__(a, b)(includingobject.__eq__())a != b➠operator.__ne__(a, b)(includingobject.__ne__())a < b➠operator.__lt__(a, b)a <= b➠operator.__le__(a, b)a > b➠operator.__gt__(a, b)a >= b➠operator.__ge__(a, b)a is b➠operator.is_(a, b)a is not b➠operator.is_not(a, b)not a➠operator.not_(a)a in b➠operator.__contains__(b, a)a not in b➠operator.not_(operator.__contains__(b, a))a or b➠_temp if (_temp := a) else ba and b➠_temp if not (_temp := a) else bimport a.b➠a = __import__('a.b', globals(), locals())import a.b as c➠c = __import__('a', globals(), locals(), ['b'], 0).bfrom .a import b➠b = __import__('a', globals(), locals(), ['b'], 1).bfrom .a import b as c➠c = __import__('a', globals(), locals(), ['b'], 1).bassert ...➠ see below (post)for ...➠ see below (includingbuiltins.iter()andbuiltins.next())pass➠"pass"with ...➠ see below (post)async def ...➠ see below (post)await ...➠desugar.builtins._await(...)async for➠ see below (includingbuiltins.aiter()andbuiltins.anext())async with➠ see below (post)(c for b in a)➠ see below (post)[c for b in a]➠list(c for b in a){c for b in a}➠set(c for b in a){c: d for b in a}➠dict((c, d) for b in a)[a, b]➠list((a, b))(includes iterable unpacking){a, b}➠set((a, b))(includes iterable unpacking)(a, b)) ➠(lambda *args: args)(a, b)(includes iterable unpacking){a: b, c: d}) ➠dict(((a, b), (c, d)))(include dictionary unpacking)@decorator➠ see below (post)break➠ see below (post)continue➠ see below (post)elseclause onwhile➠ see below (post)elifandelseclauses onif➠ see below (post)elseclause ontry➠ see below (post)finallyclause ontry➠ see below (post)raise A from B➠ see below (post)x[A, B]➠type(x).__getitem__(x, (A, B))x[A, B] = C➠type(x).__setitem__(x, (A, B), C)del x[A, B]➠type(x).__delitem__(x, (A, B))A:B:C➠slice(A, B, C)4+3j➠complex(4, 3)True➠bool(1)False➠bool(0)None➠ see below (post)b"ABC"➠bytes([65, 66, 67])"ABC"➠bytes([65, 66, 67]).decode("utf-8")...➠Ellipsisclass A: ...➠ see below (post).;` ➠ newline plus proper indentationif ...: ...➠ see below (post)a := bsee the postlambda a: b➠ see below (post)global A; A = 42➠getattr(dict, "__setitem__")(globals(), "A", 42)del A➠ see below (post)
assert a, b➠
if __debug__:
if not a:
raise AssertionError(b)assert a➠
if __debug__:
if not a:
raise AssertionErrorfor a in b:
c➠
_iter = iter(b)
while True:
try:
a = next(_iter)
except StopIteration:
break
else:
c
del _iterfor 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, _loopingwith 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 spam():
...➠
@types.coroutine
def spam():
...async for a in b:
c➠
_iter = aiter(b)
while True:
try:
a = await anext(_iter)
except StopAsyncIteration:
break
else:
c
del _iterasync 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, _loopingasync 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)(c for b in a)➠
def _gen_exp(_leftmost_iterable):
for b in _leftmost_iterable:
yield c
_gen_exp(a)@decorator
def func():
...➠
def func():
...
_temp_func_name = func
del func
func = decorator(_temp_func_name)while x:
break➠
class _BreakStatement(Exception):
pass
try:
while x:
raise _BreakStatement
except BreakStatement:
passwhile x:
continue➠
class _ContinueStatement(Exception):
pass
while x:
try:
raise _ContinueStatement
except ContinueStatement:
passwhile x:
break
else:
...➠
class _BreakStatement(Exception):
pass
try:
while x:
raise _BreakStatement
except _BreakStatement:
pass
else:
...if A:
B➠
class _Done(Exception):
pass
try:
while A:
B
raise _Done
except _Done:
passif A:
B
elif C:
D
else:
E➠
_B_ran = _D_ran = False
if A:
_B_ran = True
B
if not _B_ran and C:
_D_ran = True
D
if not (_B_ran or _D_ran):
Etry:
A
except:
B
else:
C➠
_A_finished = False
try:
A
_A_finished = True
except:
B
if _A_finished:
Ctry:
A
except Exception:
B
finally:
C➠
try:
try:
A
except Exception:
B
except BaseException:
C
raise
Craise A from B➠
_raise = A
if isinstance(_raise, type) and issubclass(_raise, BaseException):
_raise = _raise()
elif not isinstance(_raise, BaseException):
raise TypeError("exceptions must derive from BaseException")
_from = B
if isinstance(_from, type) and issubclass(_from, BaseException):
_from = _from()
if _from is not None:
_raise.__cause__ = _from
raise _raiseNone➠
def _None():
pass
_None()class Example(SuperClass):
"""Docstring."""
a: int = 3
def c(self): return 42➠
def _exec_Example(_ns):
_temp_ns = {}
_temp_ns["__module__"] = _ns["__module__"] = __name__
_temp_ns[__"qualname__"] = _ns["__qualname__"] = "Example"
_temp_ns["__doc__"] = _ns["__doc__"] = """Docstring."""
_temp_ns["__annotations__"] = _ns["__annotations__"] = {"a": int}
_temp_ns["a"] = _ns["a"] = 3
def _method_c(self):
return 42
_method_c.__name__ = "c"
_method_c.__qualname__ = "Example.c"
temp_ns["c"] = _ns["c"] = _method_c
del _method_c
def _class_Example():
# Resolving MRO entries.
bases = types.resolve_bases((SuperClass, ))
# Determining the appropriate metaclass **and**
# preparing the class namespace.
meta, ns, kwds = types.prepare_class("Example", bases)
# Executing the class body.
_exec_Example(ns)
# Creating the class object.
cls = meta("Example", bases, ns)
## Class decorators, if there were any.
## Make the namespace read-only.
cls.__dict__ = read_only_proxy(ns)
return cls
Example = _class_Example()lambda A: B➠
def _lambda(A):
return B
_lambda.__name__ = "<lambda>"del A➠
_DELETED = object()
# `del A`
A = _DELETED
# Referencing `A`
if A is _DELETED:
raise UnboundLocalError("cannot access local variable 'A' where it is not associated with a value")try:
gettattr(globals(), "__delitem__")("A")
except KeyError:
raise NameError("name 'A' is not defined")Taken from the keyword module.
Nothing; all unravelled!
Taken from the token module.