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Error accessing named tuple defined within import cycle #3054

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JukkaL opened this issue Mar 24, 2017 · 1 comment · Fixed by #3952
Closed

Error accessing named tuple defined within import cycle #3054

JukkaL opened this issue Mar 24, 2017 · 1 comment · Fixed by #3952

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@JukkaL
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JukkaL commented Mar 24, 2017

Mypy doesn't recognize access to a named tuple defined in another module within an import cycle, if the other module is processed later than the module that contains the reference to the named tuple.

Example:

# a.py
from collections import namedtuple
from b import f
N = namedtuple('N', 'a')
# b.py
import a
def f(x: a.N) -> None: ...  # Invalid type "a.N"

A potential fix is to process references to types in a later phase of semantic analysis than type definitions.

This is related to #3016.

@ilevkivskyi
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The same is true for TypedDicts and probably for all other "made-up" TypoInfos created during the second pass (not during the first, like for normal classes).

JukkaL pushed a commit that referenced this issue Sep 27, 2017
Forward references didn't work with anything apart from classes, for example 
this didn't work:

```
x: A
A = NamedTuple('A', [('x', int)])
```

The same situation was with `TypedDict`, `NewType`, and type aliases. The 
root problem is that these synthetic types are neither detected in first pass, 
nor fixed in third pass. In certain cases this can lead to crashes (first six issues 
below are various crash scenarios). This fixes these crashes by applying some 
additional patches after third pass.

Here is the summary of the PR:

* New simple wrapper type `ForwardRef` with only one field `link` is introduced 
  (with updates to type visitors)
* When an unknown type is found in second pass, the corresponding 
  `UnboundType` is wrapped in `ForwardRef`, it is given a "second chance" in 
  third pass.
* After third pass I record the "suspicious" nodes, where forward references and 
  synthetic types have been encountered and append patches (callbacks) to fix 
  them after third pass. Patches use the new visitor `TypeReplacer` (which is the 
  core of this PR).

Fixes #3340
Fixes #3419
Fixes #3674
Fixes #3685
Fixes #3799
Fixes #3836
Fixes #3881
Fixes #867
Fixes #2241
Fixes #2399
Fixes #1701
Fixes #3016
Fixes #3054
Fixes #2762
Fixes #3575
Fixes #3990
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