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#2164·pytube

[BUG - RegexMatchError in `cypher.py`]

Author: posfr2Created Nov 6, 2025Updated Nov 7, 2025
Labelsbug

RegexMatchError in cypher.py

Both a very simple Python script and the command line utility give the same error; namely:

File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 209, in get_initial_function_name raise RegexMatchError(caller="get_initial_function_name", pattern="multiple") pytube.exceptions.RegexMatchError: get_initial_function_name: could not find match for multiple

The error appears to occur in file cipher.py.

Below is the Powershell log of the run via the command line. As shown at the top of the log, the versions are:

Python 3.14.0 pytube 15.0.16

The PowerShell Log now follows:

powershell
PS Thu 06/11 15:48 C:\Users\Home\tmp > python --version
Python 3.14.0
PS Thu 06/11 15:48 C:\Users\Home\tmp > pytube --version
python.exe C:\Users\Home\AppData\Local\Programs\Python\Python314\Scripts\pytube 15.0.16
PS Thu 06/11 15:48 C:\Users\Home\tmp > pytube https://youtube.com/watch?v=2lAe1cqCOXo
Loading video...
Traceback (most recent call last):
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\__main__.py", line 184, in fmt_streams
    extract.apply_signature(stream_manifest, self.vid_info, self.js)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\extract.py", line 401, in apply_signature
    cipher = Cipher(js=js)
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 30, in __init__
    self.transform_plan: List[str] = get_transform_plan(js)
                                     ~~~~~~~~~~~~~~~~~~^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 232, in get_transform_plan
    name = re.escape(get_initial_function_name(js))
                     ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 209, in get_initial_function_name
    raise RegexMatchError(caller="get_initial_function_name", pattern="multiple")
pytube.exceptions.RegexMatchError: get_initial_function_name: could not find match for multiple

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Scripts\pytube.exe\__main__.py", line 6, in <module>
    sys.exit(main())
             ~~~~^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cli.py", line 53, in main
    _perform_args_on_youtube(youtube, args)
    ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cli.py", line 60, in _perform_args_on_youtube
    download_highest_resolution_progressive(
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^
        youtube=youtube, resolution="highest", target=args.target
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cli.py", line 474, in download_highest_resolution_progressive
    stream = youtube.streams.get_highest_resolution()
             ^^^^^^^^^^^^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\__main__.py", line 312, in streams
    return StreamQuery(self.fmt_streams)
                       ^^^^^^^^^^^^^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\__main__.py", line 191, in fmt_streams
    extract.apply_signature(stream_manifest, self.vid_info, self.js)
    ~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\extract.py", line 401, in apply_signature
    cipher = Cipher(js=js)
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 30, in __init__
    self.transform_plan: List[str] = get_transform_plan(js)
                                     ~~~~~~~~~~~~~~~~~~^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 232, in get_transform_plan
    name = re.escape(get_initial_function_name(js))
                     ~~~~~~~~~~~~~~~~~~~~~~~~~^^^^
  File "C:\Users\Home\AppData\Local\Programs\Python\Python314\Lib\site-packages\pytube\cipher.py", line 209, in get_initial_function_name
    raise RegexMatchError(caller="get_initial_function_name", pattern="multiple")
pytube.exceptions.RegexMatchError: get_initial_function_name: could not find match for multiple
PS Thu 06/11 15:49 C:\Users\Home\tmp >

Source: pytube/pytube

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