Variable used before definition

Environment data

VS Code version: 1.29.1 (1.29.1)
Extension version (available under the Extensions sidebar): 2018.11.0
OS and version: macOS Mojave 10.14.1 (18B75)
Python version (& distribution if applicable, e.g. Anaconda): Python 3.7.1 64-bit
Type of virtual environment used (N/A | venv | virtualenv | conda | ...): venv
Relevant/affected Python packages and their versions: -

Expected behaviour

When running provided code snippet there should be no warning.

from typing import Dict

fallbackName: Dict[str, str] = {"firstName": "First", "lastName": "Last"}

NAME = " ".join(str(x) for x in fallbackName.values())

print(f"Hi, {NAME}!")

Actual behaviour

A warning is generated: 'fallbackName' used before definition

{
	"resource": "/Users/_____/Projects/python/sandbox/index.py",
	"owner": "_generated_diagnostic_collection_name_#0",
	"code": "use-before-def",
	"severity": 4,
	"message": "'fallbackName' used before definition",
	"source": "Python",
	"startLineNumber": 5,
	"startColumn": 33,
	"endLineNumber": 5,
	"endColumn": 45
}

Additional Info

This does not happen when type hinting is removed:

FALLBACK_NAME = {"first_name": "First", "last_name": "Last"}

NAME = " ".join(str(x) for x in FALLBACK_NAME.values())

print(f"Hi, {NAME}!")

Steps to reproduce:

Create a new project, python3 -m venv new/venv.
Insert code into new/index.py.
Lint.

Logs

Output for Python in the Output panel (View→Output, change the drop-down the upper-right of the Output panel to Python)

Starting Microsoft Python language server.
Microsoft Python Language Server version 0.1.66.0
Initializing for /Users/_____/Projects/python/sandbox/venv/bin/python
##########Linting Output - prospector##########
{
  "summary": {
    "started": "2018-12-08 12:13:01.666245",
    "libraries": [],
    "strictness": "from profile",
    "profiles": ".prospector.yaml, full_pep8, doc_warnings, strictness_veryhigh, no_member_warnings",
    "tools": [
      "dodgy",
      "mccabe",
      "mypy",
      "pep257",
      "pep8",
      "profile-validator",
      "pyflakes",
      "pylint"
    ],
    "message_count": 0,
    "completed": "2018-12-08 12:13:02.171521",
    "time_taken": "0.51",
    "formatter": "json"
  },
  "messages": []
}

Output from Console under the Developer Tools panel (toggle Developer Tools on under Help)

 INFO no standard startup: not a new window
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Create file systemwatcher with pattern */python
console.ts:134 [Extension Host] Python Extension: Create file systemwatcher with pattern */*/python
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Register Intepreter Watcher, Arg 1: {"$mid":1,"fsPath":"/Users/_____/Projects/python/sandbox","external":"file:///Users/_____/Projects/python/sandbox","path":"/Users/_____/Projects/python/sandbox","scheme":"file"}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Create file systemwatcher with pattern */python
console.ts:134 [Extension Host] Python Extension: Create file systemwatcher with pattern */*/python
console.ts:134 [Extension Host] Python Extension: Display locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Notify locators are locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Detected refreshing of Interpreters, Arg 1: {}, Return Value: 
console.ts:134 [Extension Host] Python Extension: Build the workspace interpreter watcher, Arg 1: {"$mid":1,"fsPath":"/Users/_____/Projects/python/sandbox","external":"file:///Users/_____/Projects/python/sandbox","path":"/Users/_____/Projects/python/sandbox","scheme":"file"}, Return Value: UNABLE TO DETERMINE VALUE
console.ts:134 [Extension Host] Python Extension: Register Intepreter Watcher, Arg 1: undefined, Return Value: 
console.ts:134 [Extension Host] Python Extension: Build the workspace interpreter watcher, Arg 1: undefined, Return Value: UNABLE TO DETERMINE VALUE
console.ts:134 [Extension Host] Python Extension: Get language server folder name, , Return Value: "languageServer.0.1.66"
6console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Hide locator refreshing progress, , Return Value: 
console.ts:134 [Extension Host] Python Extension: All locators have completed locating, , Return Value: 
console.ts:134 [Extension Host] Python Extension: Checking whether locactors have completed locating, , Return Value:

I have a similar issue with my Python.
VS Code version: 1.29.1 (1.29.1)
Extension version (available under the Extensions sidebar): 2018.11.0
OS and version: Ubuntu 18.04.1 LTS
Python version (& distribution if applicable, e.g. Anaconda): Python 3.6.7 64-bit
Type of virtual environment used (N/A | venv | virtualenv | conda | ...): conda
Relevant/affected Python packages and their versions: not relevant

Issues disappear if you reload window, but reappear if I make even the slightest edit to the code written. Sometimes they appear as I type (e.g. I type "return True" and issues are " 're' used before definition", " 'ret' used before definition" and so on).

Issue appears to occur more in longer files.

Yehor Borkov (@yehorb)

Yehor Borkov (@yehorb) Could you create a minimal Github repo with a reproducible error? It will help a lot in fixing this issue.

In my case, this happens because of typing.

Here:
https://github.com/yehorb/VSCode-use-before-def-bug

This is the output I get:

Yehor Borkov (@yehorb)

Yehor Borkov (@yehorb) Awesome, thanks! Now it's just waiting for a maintainer to triage this issue. 🤷‍♂️

I'm encountering a very similar problem with class variable type annotations.

class TestClass:
    instance_var: str

    def __init__(self) -> None:
        self.instance_var = ""

produces

{
	"owner": "_generated_diagnostic_collection_name_#1",
	"code": "use-before-def",
	"severity": 4,
	"message": "'instance_var' used before definition",
	"source": "Python",
	"startLineNumber": 2,
	"startColumn": 5,
	"endLineNumber": 2,
	"endColumn": 17
}

By adding a typed class variable, the error disappears (no problems are detected):

from typing import ClassVar

class TestClass:
    instance_var: str
    class_var: ClassVar[int] = 0

    def __init__(self) -> None:
        self.instance_var = ""

Omitting the type annotation on the class variable will cause the previous error on the instance variable to show up again:

class TestClass:
    instance_var: str
    class_var = 0

    def __init__(self) -> None:
        self.instance_var = ""

produces

{
	"owner": "_generated_diagnostic_collection_name_#1",
	"code": "use-before-def",
	"severity": 4,
	"message": "'instance_var' used before definition",
	"source": "Python",
	"startLineNumber": 2,
	"startColumn": 5,
	"endLineNumber": 2,
	"endColumn": 17
}

VS Code version: 1.31.0
Extension version (available under the Extensions sidebar): 2019.1.0
OS and version: Windows 10 1803
Python version (& distribution if applicable, e.g. Anaconda): CPython 3.7.0
Python Language Server version: 0.1.78

Having a similar issue... It's really frustrating.

Doing some very basic DRF stuff with django rest and these things keep popping up :(

I'm also having the same issue but with dataclasses. Every attribute gets unterlined with a use-before-def message.

Interestingly, assigning a default value makes the Language Server stop complaning:

Philipp Weidenhiller (@phwh)

Philipp Weidenhiller (@phwh) reported in microsoft/python-language-server#399 .

If an even more minimal example would help:

test: list = [1, 2]

a = [2*i for i in test]

@millsyman please report on the upstream issue.

Original issue is fixed upstream (microsoft/python-language-server#475)

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Variable used before definition #3598

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Variable used before definition #3598

Description

Environment data

Expected behaviour

Actual behaviour

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Steps to reproduce:

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yehorb commented on Dec 8, 2018

azdanov commented on Dec 9, 2018

yehorb commented on Dec 10, 2018

azdanov commented on Dec 10, 2018

mcpower commented on Feb 7, 2019

mr-katsini commented on Feb 11, 2019

phwh commented on Feb 14, 2019

brettcannon commented on Feb 15, 2019

inthesmall commented on Mar 6, 2019

brettcannon commented on Mar 7, 2019

luabud commented on Sep 11, 2019

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