False positive unreachable when variable is set and reset inside loop
#14987
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bug
mypy got something wrong
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Similar problem here while using mypy==1.3.0. My example code: data = """
{foo}
bar >
baz
"""
prompt = None
reponse = None
lines = data.splitlines()
for line in lines:
if prompt and reponse: # mypy error: Right operand of "and" is never evaluated [unreachable]
print("Break reached!") # mypy error: Statement is unreachable [unreachable]
break
if not prompt and line.endswith(">"):
prompt = line
continue
if not reponse and line.endswith("}"):
reponse = line
continueRun output: |
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|
+1 Here is a smaller example: state = None
for x in 'ab':
if state is not None:
print('reachable')
state = 'x'The script output: Mypy error: main.py:4:9: error: Statement is unreachable [unreachable]
print('reachable')
^~~~~~~~~~~~~~~~~~
Found 1 error in 1 file (checked 1 source file)
✕ mypy failed. |
|
Nice, thanks for the ping |
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I tend to think the problem underlying the initial example has nothing to do with loops but with promotions, because both So, maybe this is a simpler repro: x: float | None
y: int | None
z: int
reveal_type(x) # float | None
x = y
reveal_type(x) # None !!!!!!!!!
x = z
reveal_type(x) # intWith "normal" subtypes, the same type of type narrowing works: class A: ...
class B(A): ...
a: A | None
b: B | None
c: B
reveal_type(a) # A | None
a = b
reveal_type(a) # B | None
a = c
reveal_type(a) # BLikely, an attempt to solve this could start here: |
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Bug Report
mypy warns about the right side of a condition being unreachable when a variable is reset in an outer loop, then set again inside the inner loop.
To Reproduce
Expected Behavior
No error.
Actual Behavior
mypy outputs
error: Right operand of "or" is never evaluated. This is clearly because the type oftestis re-evaluated at some point, even though it was declared with a type and no statement narrows that type.This appears related to #7204, #8721, #8865, #13973, #14120, except it can't be solved by declaring the type of the variable before the loop in which it's updated (because that violates
no-redef).Note: I'm not sure why anyone would want to actually do this in practice. But I thought it might provide a useful test case.
Your Environment
mypy.ini(and other config files): NoneThe text was updated successfully, but these errors were encountered: