Error map

NameError NameError: name 'x' is not defined

Python · layer 4, Application & API

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1 · On your device 4 · Application & API 5 · Data 6 · Platform & cloud
NameError — NameError: name 'x' is not defined (Python)NameErrorModuleNotFoundError — ModuleNotFoundError: No module named 'x' (Python)ModuleNotFoundErrorReferenceError — ReferenceError: x is not defined (JavaScript)ReferenceErrorUnboundLocalError — UnboundLocalError: cannot access local variable 'x' where it is not associated with a value (Python)UnboundLocalErrorIndentationError — IndentationError: unexpected indent / expected an indented block (Python)IndentationErroralready declared — SyntaxError: Identifier 'x' has already been declared (JavaScript)already declaredCS0103 — error CS0103: The name 'x' does not exist in the current context (.NET)CS0103TDZ — ReferenceError: Cannot access 'x' before initialization (JavaScript)TDZMODULE_NOT_FOUND — Error: Cannot find module 'x' (MODULE_NOT_FOUND) (Node.js)MODULE_NOT_FOUNDClass not found — PHP Fatal error: Uncaught Error: Class "X" not found (PHP)Class not foundImportError — ImportError: cannot import name 'x' from 'y' (Python)ImportErrorTypeError — TypeError: Cannot read properties of undefined (reading 'x') (JavaScript)TypeErrorTypeError: not a function — TypeError: x is not a function (JavaScript)TypeError: not a fu…Hydration failed — Error: Hydration failed because the initial UI does not match what was rendered on the server (React)Hydration failedAttributeError — AttributeError: 'X' object has no attribute 'y' (Python)AttributeErrorConnectionRefusedError — ConnectionRefusedError: [Errno 111] Connection refused (Python)ConnectionRefusedEr…Event loop is closed — RuntimeError: Event loop is closed (Python)Event loop is closedParse error — PHP Parse error: syntax error, unexpected … (PHP)Parse errorcompose validation — docker compose: services.x Additional property y is not allowed / yaml: line N: mapping values are not allowed (Docker)compose validationawait outside async — SyntaxError: await is only valid in async functions and the top level bodies of modules (JavaScript)await outside asyncUnexpected token < — SyntaxError: Unexpected token '<' (HTML served instead of JavaScript) (JavaScript)Unexpected token <unexpected end of input — SyntaxError: Unexpected end of input (JavaScript)unexpected end of i…missing ) — SyntaxError: missing ) after argument list (JavaScript)missing )CS0246 — error CS0246: The type or namespace name 'X' could not be found (are you missing a using directive or an assembly reference?) (.NET)CS0246CS1061 — error CS1061: 'X' does not contain a definition for 'Y' and no accessible extension method 'Y' accepting a first argument of type 'X' could be found (.NET)CS1061CS8618 — warning CS8618: Non-nullable property 'X' must contain a non-null value when exiting constructor. Consider declaring the property as nullable (.NET)CS8618not a constructor — TypeError: x is not a constructor (JavaScript)not a constructor1046 — MySQL ERROR 1046 (3D000): No database selected (MySQL)10461153 — MySQL ERROR 1153 (08S01): Got a packet bigger than 'max_allowed_packet' bytes (MySQL)1153

Directly related (7)

ModuleNotFoundErrorPython

ModuleNotFoundError: No module named 'x'

Python can’t find the module you import — it isn’t installed in the interpreter/virtualenv that’s running, or the import path is…

ReferenceErrorJavaScript

ReferenceError: x is not defined

Code refers to a variable or function name that doesn’t exist in the current scope.

UnboundLocalErrorPython

UnboundLocalError: cannot access local variable 'x' where it is not associated with a value

A function assigns to a variable somewhere, which makes it local everywhere in that function — so reading it before the assignmen…

IndentationErrorPython

IndentationError: unexpected indent / expected an indented block

Python’s block structure is broken — inconsistent indentation or mixed tabs and spaces.

already declaredJavaScript

SyntaxError: Identifier 'x' has already been declared

The same let/const/class name was declared twice in the same scope.

CS0103.NET

error CS0103: The name 'x' does not exist in the current context

The identifier isn’t declared in scope — typo, variable declared in another block, missing using static, or a Razor/partial class…

TDZJavaScript

ReferenceError: Cannot access 'x' before initialization

A let/const/class was used before its declaration line ran (temporal dead zone) — often a circular import.

Two steps away (21)

MODULE_NOT_FOUNDNode.js

Error: Cannot find module 'x' (MODULE_NOT_FOUND)

Node can’t resolve the module path — the package isn’t installed, or a relative path/extension is wrong.

Class not foundPHP

PHP Fatal error: Uncaught Error: Class "X" not found

PHP couldn’t load the class — autoloading failed, the namespace is wrong, or the dependency isn’t installed.

ImportErrorPython

ImportError: cannot import name 'x' from 'y'

The module was found, but the name you’re importing from it doesn’t exist — usually a version change or a circular import.

TypeErrorJavaScript

TypeError: Cannot read properties of undefined (reading 'x')

You tried to access a property on a value that is `undefined` (or `null`) — usually data that hasn’t loaded yet or a wrong proper…

TypeError: not a functionJavaScript

TypeError: x is not a function

You called something as a function, but its value is not a function (it’s undefined, a string, an object…).

Hydration failedReact

Error: Hydration failed because the initial UI does not match what was rendered on the server

The HTML rendered on the server differs from the first client render, so React (Next.js/Remix) can’t attach to it.

AttributeErrorPython

AttributeError: 'X' object has no attribute 'y'

You accessed an attribute or method that doesn’t exist on that object type.

ConnectionRefusedErrorPython

ConnectionRefusedError: [Errno 111] Connection refused

Nothing is listening on the host/port Python tried to connect to.

Event loop is closedPython

RuntimeError: Event loop is closed

Async code tried to use an event loop that has already been shut down.

Parse errorPHP

PHP Parse error: syntax error, unexpected …

PHP can’t parse the file because of a syntax mistake — the real error is often on the line before the one reported.

compose validationDocker

docker compose: services.x Additional property y is not allowed / yaml: line N: mapping values are not allowed

The compose file is invalid YAML or uses a key Compose doesn’t recognise at that level (usually an indentation mistake).

await outside asyncJavaScript

SyntaxError: await is only valid in async functions and the top level bodies of modules

await was used inside a function that isn’t async (or in a classic, non-module script).

Unexpected token <JavaScript

SyntaxError: Unexpected token '<' (HTML served instead of JavaScript)

The browser loaded a .js file but received HTML (an error page or the SPA index.html).

unexpected end of inputJavaScript

SyntaxError: Unexpected end of input

The parser reached the end of the code (or JSON) while still expecting more — a missing } ) ] or empty JSON.

missing )JavaScript

SyntaxError: missing ) after argument list

A function call’s parentheses are unbalanced — often an unescaped quote or a missing comma/plus.

CS0246.NET

error CS0246: The type or namespace name 'X' could not be found (are you missing a using directive or an assembly reference?)

The compiler doesn’t know the type — missing using, missing NuGet package/project reference, or a target framework mismatch.

CS1061.NET

error CS1061: 'X' does not contain a definition for 'Y' and no accessible extension method 'Y' accepting a first argument of type 'X' could be found

The member you call doesn’t exist on that type — typo, wrong type, missing using for an extension method, or an API removed in a…

CS8618.NET

warning CS8618: Non-nullable property 'X' must contain a non-null value when exiting constructor. Consider declaring the property as nullable

With nullable reference types enabled, a non-nullable reference property isn’t initialised by the constructor.

not a constructorJavaScript

TypeError: x is not a constructor

new was used with something that isn’t a class/constructor — usually a wrong import.

1046MySQL

MySQL ERROR 1046 (3D000): No database selected

A query referenced tables without a database selected (no USE and no db in the connection).

1153MySQL

MySQL ERROR 1153 (08S01): Got a packet bigger than 'max_allowed_packet' bytes

A single statement or row exceeded max_allowed_packet — big BLOBs, huge INSERTs or large dump lines.

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