Variable used before definition

[azdanov]

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:

1. Create a new project, python3 -m venv new/venv.
2. Insert code into new/index.py.
3. 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: 

[yehorb]

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.

[azdanov]

@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.

[yehorb]

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

This is the output I get:

[azdanov]

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

[mcpower]

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

[mr-katsini]

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

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

[phwh]

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:

[brettcannon]

@phwh reported in microsoft/python-language-server#399 .

[inthesmall]

If an even more minimal example would help:

test: list = [1, 2]

a = [2*i for i in test]

[brettcannon]

@millsyman please report on the upstream issue.

[luabud]

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