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TypedDict.get returns an object if a dictionary has more than one field and the types on those fields differ. #2612

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rowillia opened this issue Dec 27, 2016 · 1 comment
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TypedDict.get returns an object if a dictionary has more than one field and the types on those fields differ. #2612

rowillia opened this issue Dec 27, 2016 · 1 comment
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@JukkaL
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feature priority-0-high topic-typed-dict

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@rowillia
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rowillia commented Dec 27, 2016 •
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This appears to be due to TypedDict relying on a fallback.

from typing import List, Optional
from mypy_extensions import TypedDict

TaggedPoint = TypedDict('TaggedPoint', {'type': str, 'x': int, 'y': int})
Point3D = TypedDict('Point3D', {'x': int, 'y': int, 'z': int})
BadPointSet = TypedDict('BadPointSet', {
    'total_length': int,
    'points': List[TaggedPoint]
})
OKPointSet = TypedDict('OKPointSet', {
    'points': List[TaggedPoint]
})

def foo(point_3d: Point3D,
        tagged_point: TaggedPoint,
        bad_points: BadPointSet,
        ok_points: OKPointSet) -> None:
    reveal_type(point_3d.get('x'))  # error: Revealed type is 'builtins.int*
    reveal_type(tagged_point.get('x'))  # error: Revealed type is 'builtins.object*
    reveal_type(bad_points.get('points'))  # error: Revealed type is 'builtins.object*'
    reveal_type(ok_points.get('points'))  # Revealed type is 'builtins.list*[TypedDict(x=builtins.int, y=builtins.int, _fallback=test_typed_dict_get.TaggedPoint)]'
@rowillia rowillia changed the title TypedDict.get returns an object if a dictionary has more than one field and one of those fields is a Generic TypedDict.get returns an object if a dictionary has more than one field and the types on those fields differ. Dec 28, 2016
rowillia pushed a commit to rowillia/mypy that referenced this issue Dec 28, 2016
Implement type-aware get for TypedDict
0de22fc 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
@rowillia rowillia mentioned this issue Dec 28, 2016
Closed
rowillia pushed a commit to rowillia/mypy that referenced this issue Dec 28, 2016
Implement type-aware get for TypedDict
586c1fd 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
@JukkaL JukkaL mentioned this issue Jan 3, 2017
Closed
rowillia pushed a commit to rowillia/mypy that referenced this issue Jan 6, 2017
Implement type-aware get for TypedDict
e30a603 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
rowillia pushed a commit to rowillia/mypy that referenced this issue Jan 7, 2017
Implement type-aware get for TypedDict
fddf3da 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
rowillia pushed a commit to rowillia/mypy that referenced this issue Jan 11, 2017
Implement type-aware get for TypedDict
4028dfc 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
rowillia pushed a commit to rowillia/mypy that referenced this issue Jan 11, 2017
Implement type-aware get for TypedDict
21a28af 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
rowillia pushed a commit to lyft/mypy that referenced this issue Jan 12, 2017
Implement type-aware get for TypedDict
4c3cb1b 
Previously, `get` would simply fallback to the type of the underlying dictionary which made
TypedDicts hard to use with code that's parsing objects where fields may or may not be
present (for example, parsing a response).

This implementation _explicitly_ ignores the default parameter's type as it's quite useful to
chain together get calls (Until something like PEP 505 hits 😄)

```python
foo.get('a', {}).get('b', {}).get('c')
```

This fixes python#2612
@gvanrossum gvanrossum assigned JukkaL and unassigned rowillia May 22, 2017
@gvanrossum
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Jukka wants to redo this using a plugin.

@JukkaL JukkaL mentioned this issue Jun 6, 2017
Merged
JukkaL added a commit that referenced this issue Jun 7, 2017
@JukkaL
Refactor plugin system and special case TypedDict get and int.__pow__ (…
bcf89b1 
…#3501)

Implement a general-purpose way of extending type inference of
methods. Also special case TypedDict get and `int.__pow__`.
Implement a new plugin system that can handle both module-level 
functions and methods.

This an alternative to #2620 by @rowillia. I borrowed some test
cases from that PR. This PR has a few major differences:

* Use the plugin system instead of full special casing.
* Don't support `d.get('x', {})` as it's not type safe. Once we
  have #2632 we can add support for this idiom safely.
* Code like `f = foo.get` loses the special casing for get.

Fixes #2612. Work towards #1240.
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Implement type-aware get for TypedDict rowillia/mypy
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