What causes "No such file" in ytdl-org/youtube-dl?

Check what the class actually exposes: print(sorted(avm_class.methods)) and call the correct name.

ytdl-org/youtube-dl · error · HTTPError

No such file

Error message

No such file

What it means

Raised by SWFInterpreter.extract_function when the requested function is neither patched (patch_function), a previously interpreted pyfunction, a class name (constructor path), nor present in avm_class.methods. The interpreter only knows methods that were registered from the ABC's trait tables, so asking for anything else (an inherited member, a dynamic property, or a misspelled name) fails here.

Source

Thrown at devscripts/buildserver.py:359

        except subprocess.CalledProcessError as e:
            raise BuildError(e.output)

        super(YoutubeDLBuilder, self).build()


class DownloadBuilder(object):
    def __init__(self, **kwargs):
        self.handler = kwargs.pop('handler')
        self.srcPath = os.path.join(self.buildPath, *tuple(kwargs['path'][2:]))
        self.srcPath = os.path.abspath(os.path.normpath(self.srcPath))
        if not self.srcPath.startswith(self.buildPath):
            raise HTTPError(self.srcPath, 401)

        super(DownloadBuilder, self).__init__(**kwargs)

    def build(self):
        if not os.path.exists(self.srcPath):
            raise HTTPError('No such file', 404)
        if os.path.isdir(self.srcPath):
            raise HTTPError('Is a directory: %s' % self.srcPath, 401)

        self.handler.send_response(200)
        self.handler.send_header('Content-Type', 'application/octet-stream')
        self.handler.send_header('Content-Disposition', 'attachment; filename=%s' % os.path.split(self.srcPath)[-1])
        self.handler.send_header('Content-Length', str(os.stat(self.srcPath).st_size))
        self.handler.end_headers()

        with open(self.srcPath, 'rb') as src:
            shutil.copyfileobj(src, self.handler.wfile)

        super(DownloadBuilder, self).build()


class CleanupTempDir(object):
    def build(self):
        try:

View on GitHub (pinned to 956b8c5855)

Solutions

Check what the class actually exposes: print(sorted(avm_class.methods)) and call the correct name.
If the function lives on a superclass, extract that class first (extract_class(super_name)) and call extract_function on it.
Bypass interpretation with interpreter.patch_function(avm_class, 'name', python_replacement) — the mechanism swfinterp itself provides for exactly this gap.
Update youtube-dl / switch to yt-dlp; the extractor's expected function name may have been refreshed.

Example fix

# before
func = interpreter.extract_function(avm_class, 'decrypt')
sig = func([sig])

# after: patch the method with a Python implementation
interpreter.patch_function(avm_class, 'decrypt', lambda args: my_decrypt(args[0]))
func = interpreter.extract_function(avm_class, 'decrypt')
sig = func([sig])

Defensive patterns

Strategy: fallback

Validate before calling

# check all resolution paths extract_function uses, in order
func = (interpreter._patched_functions.get((avm_class, name))
        or avm_class.method_pyfunctions.get(name)
        or (interpreter._classes_by_name[name].make_object()
            if name in interpreter._classes_by_name else None)
        or avm_class.methods.get(name))
if func is None:
    raise ExtractorError('Cannot find function %s.%s' % (avm_class.name, name))

Type guard

def has_function(interp, avm_class, name: str) -> bool:
    return ((avm_class, name) in interp._patched_functions
            or name in avm_class.method_pyfunctions
            or name in interp._classes_by_name
            or name in avm_class.methods)

Try / catch

from youtube_dl.utils import ExtractorError
try:
    func = interpreter.extract_function(avm_class, 'decrypt')
except ExtractorError as e:
    if 'Cannot find function' in str(e):
        interpreter.patch_function(avm_class, 'decrypt', lambda args: py_decrypt(args[0]))
        func = interpreter.extract_function(avm_class, 'decrypt')
    else:
        raise

Prevention

Check avm_class.methods (and the superclass) for the function name before calling.
Use patch_function for any method you can implement in Python — it is the intended escape hatch.
Remember constructors resolve via _classes_by_name, not methods; a missing name may be a class, not a function.

When it happens

Trigger: Calling extract_function(avm_class, 'name') where 'name' is not in avm_class.methods. Common when the method lives on a superclass or was added as a script-level function; or when an extractor's expected function name changed after a player update.

Common situations: Player SWF refactors move the deciphering function to another class or rename it; extracting a function before class initialization (cinit) has registered dynamic methods; simple name typos in custom swfinterp code.

Related errors

AI-assisted analysis of ytdl-org/youtube-dl@956b8c5855 (2026-08-14). Data as JSON: /api/errors/24e4cc2c29b16171. Report an issue: GitHub.