Constant fold more unary and binary expressions #15202
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Unfortunately mypy can't easily support storing the bytes value for final references. Other than preventing b"foo" + CONST_BYTES from being folded, it also means this commit is mypyc-only.
| try: | ||
| ret = left**right | ||
| except OverflowError: | ||
| return None |
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Digging through the CPython source, only power ops can raise an OverflowError.
| @@ -3356,7 +3356,7 @@ def analyze_simple_literal_type(self, rvalue: Expression, is_final: bool) -> Typ | |||
| return None | |||
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| value = constant_fold_expr(rvalue, self.cur_mod_id) | |||
| if value is None: | |||
| if value is None or isinstance(value, complex): | |||
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I have no idea whether complex literals make any sense in mypy. PTAL.
| value = node.final_value | ||
| if isinstance(value, (CONST_TYPES)): | ||
| return value | ||
| final_value = node.final_value |
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The value local name should support ConstantValue | None, but Var.final_value does not support bytes. To avoid causing type errors later in the function from this assignment implicitly setting value's type, these variables were renamed.
| real = 1 | ||
| return 5j+real |
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The intent of this change is to preserve the old test case behavior where constant folding wasn't performed.
| div = 2.0 / 0.0 | ||
| floor_div = 2.0 // 0.0 | ||
| power_imag = (-2.0)**0.5 | ||
| power_overflow = 2.0**10000.0 |
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While floats usually don't raise an error on overflow, this is the one exception I know of. This is why there's a guard against OverflowError in mypy/constant_fold.py.
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A good catch! We could also generate a compile-time error, but it's not important.
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Great, thanks! Finally got around to reviewing this. Looks good, just a few minor comments.
With these changes we probably have pretty much all the constant folding we need in the medium term at least. math constant support in final expressions might still be a good thing to have at some point, if it doesn't work yet (e.g. X: Final = math.pi * 2, see #15324).
mypy/constant_fold.py
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| if right != 0: | ||
| return left % right | ||
| elif op == "**": | ||
| if (left < 0 and right >= 1 or right == 0) or (left >= 0 and right >= 0): |
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This could return a complex number, but the return type doesn't include complex (not sure if supporting complex results is worth it):
>>> (-1.2) ** 1.5
(-2.414760036730213e-16-1.3145341380123985j)
I used this fragment to look for other interesting cases, maybe it's helpful here:
values = -1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5
for x in values:
for y in values:
try:
print(x, y, x**y)
except Exception:
print(f'error: {x} ** {y}')| add_mul = (1.5 + 3.5) * 5.0 | ||
| sub = 7.0 - 7.5 | ||
| div = 3.0 / 2.0 | ||
| floor_div = 3.0 // 2.0 |
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Test with negative operands as well?
| div = 2.0 / 0.0 | ||
| floor_div = 2.0 // 0.0 | ||
| power_imag = (-2.0)**0.5 | ||
| power_overflow = 2.0**10000.0 |
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A good catch! We could also generate a compile-time error, but it's not important.
| from typing_extensions import Final | ||
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| N: Final = 1 | ||
| FLOAT_N: Final = 1.5 |
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Is there a test case specific to a final float? If not, it would be good to add. Also test complex initializers such as N: Final = 1.5 * 2.
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According to mypy_primer, this change doesn't affect type check results on a corpus of open source code. ✅ |
(#14838 had a lot of conflicts and it was easier to fix them in a new PR)
Now mypy can constant fold these additional operations:
While this can be useful with literal types, the main goal is to improve constant folding in mypyc (mypyc/mypyc#772).
mypyc can also fold bytes addition and multiplication, but mypy cannot as byte values can't be easily stored anywhere.