Error map
UnboundLocalError UnboundLocalError: cannot access local variable 'x' where it is not associated with a value
Python · layer 4, Application & API
Centre: this error. First ring: errors it is linked with (8). Outer ring: what those are linked with. Colours show the layer of a request each error belongs to. Click any dot to re-centre the map on it; hover to follow its connections. The centre dot opens the error page.
Directly related (8)
ReferenceError: x is not defined
Code refers to a variable or function name that doesn’t exist in the current scope.
ConnectionRefusedError: [Errno 111] Connection refused
Nothing is listening on the host/port Python tried to connect to.
AttributeError: 'X' object has no attribute 'y'
You accessed an attribute or method that doesn’t exist on that object type.
NameError: name 'x' is not defined
Python doesn’t know the name — it was never assigned/imported in this scope, or it’s misspelled.
SyntaxError: Identifier 'x' has already been declared
The same let/const/class name was declared twice in the same scope.
RuntimeError: Event loop is closed
Async code tried to use an event loop that has already been shut down.
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…
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 (23)
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: 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…).
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.
Error: connect ECONNREFUSED 127.0.0.1:5432
Nothing is listening at that host:port — the target service is down or you’re connecting to the wrong address.
Cloudflare Error 521: Web Server Is Down
Cloudflare couldn’t connect to your origin — the connection was refused.
API Request Timed Out (ETIMEDOUT / ReadTimeout / timeout of 30000ms exceeded)
The client gave up waiting — either for the connection to open or for the response to arrive.
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.
KeyError: 'x'
You accessed a dictionary key that doesn’t exist.
TypeError: 'NoneType' object is not subscriptable
You used `[ ]` on a value that is `None` — typically a function that returned nothing.
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…
IndentationError: unexpected indent / expected an indented block
Python’s block structure is broken — inconsistent indentation or mixed tabs and spaces.
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).
SyntaxError: Unexpected end of input
The parser reached the end of the code (or JSON) while still expecting more — a missing } ) ] or empty JSON.
SyntaxError: missing ) after argument list
A function call’s parentheses are unbalanced — often an unescaped quote or a missing comma/plus.
Node.js: [UnhandledPromiseRejection] — This error originated either by throwing inside of an async function without a catch block
A promise rejected and nothing handled it; since Node 15 this crashes the process.
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).
AbortError: The user aborted a request. / signal is aborted without reason
A fetch was cancelled through an AbortController (or the browser cancelled it).
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.
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…
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.
TypeError: x is not a constructor
new was used with something that isn’t a class/constructor — usually a wrong import.
MySQL ERROR 1046 (3D000): No database selected
A query referenced tables without a database selected (no USE and no db in the connection).
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.
Map another error
Popular: 4035004000xC000007BTypeErrorCritical error404NullPointerException