[Bug]: Failure when installing example on Windows

[vserdyuk]

Bug description

Command

aqt install-example --outputdir D:\Qt2 windows 6.8.0

fails to complete on Windows 11 with aqt v3.1.21. Was working fine with v3.1.19.

I had some modifications in settings.ini:

• different baseurl: https://ftp.fau.de/qtproject/
• INSECURE_NOT_FOR_PRODUCTION_ignore_hash: True
• https://download.qt.io and https://master.qt.io/ moved to blacklist

[DEFAULTS]

[aqt]
concurrency: 4
baseurl: https://ftp.fau.de/qtproject/
7zcmd: 7z
print_stacktrace_on_error: False
always_keep_archives: False
archive_download_location: .
min_module_size: 41

[requests]
connection_timeout: 3.5
response_timeout: 30
max_retries_on_connection_error: 5
retry_backoff: 0.1
max_retries_on_checksum_error: 5
max_retries_to_retrieve_hash: 5
hash_algorithm: sha1
INSECURE_NOT_FOR_PRODUCTION_ignore_hash: True

[mirrors]
trusted_mirrors:
    https://ftp.fau.de/qtproject/
blacklist:
    https://download.qt.io
    http://mirrors.ocf.berkeley.edu
    http://mirrors.tuna.tsinghua.edu.cn
    http://mirrors.geekpie.club
    https://master.qt.io/
fallbacks:
    https://qtproject.mirror.liquidtelecom.com/
    https://mirrors.aliyun.com/qt/
    https://mirrors.ustc.edu.cn/qtproject/
    https://ftp.jaist.ac.jp/pub/qtproject/
    https://ftp.yz.yamagata-u.ac.jp/pub/qtproject/
    https://qt-mirror.dannhauer.de/
    https://ftp.fau.de/qtproject/
    https://mirror.netcologne.de/qtproject/
    https://mirrors.dotsrc.org/qtproject/
    https://www.nic.funet.fi/pub/mirrors/download.qt-project.org/
    https://mirrors.ukfast.co.uk/sites/qt.io/
    https://ftp2.nluug.nl/languages/qt/
    https://ftp1.nluug.nl/languages/qt/
    https://qt.mirror.constant.com/

Expected behavior

Successful download of examples

aqt and python version

aqtinstall(aqt) v3.1.21 on Python 3.12.6 [CPython MSC v.1940 64 bit (AMD64)]

Operating System

Windows

Relevant log output

D:\>aqt install-example --outputdir D:\Qt2 windows 6.8.0
INFO    : aqtinstall(aqt) v3.1.21 on Python 3.12.6 [CPython MSC v.1940 64 bit (AMD64)]
ERROR   : cannot access local variable 'extensions_xml_text' where it is not associated with a value
Traceback (most recent call last):
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\installer.py", line 180, in run
    args.func(args)
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\installer.py", line 485, in run_install_example
    self._run_src_doc_examples("examples", args, cmd_name="example")
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\installer.py", line 444, in _run_src_doc_examples
    srcdocexamples_archives: SrcDocExamplesArchives = retry_on_bad_connection(
                                                      ^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\helper.py", line 176, in retry_on_bad_connection
    return function(base_url)
           ^^^^^^^^^^^^^^^^^^
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\installer.py", line 445, in <lambda>
    lambda base_url: SrcDocExamplesArchives(
                     ^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\archives.py", line 612, in __init__
    super(SrcDocExamplesArchives, self).__init__(
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\archives.py", line 322, in __init__
    self._get_archives()
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\archives.py", line 647, in _get_archives
    self._get_archives_base(name, self._target_packages())
  File "C:\Users\Vladimir\AppData\Local\Programs\Python\Python312\Lib\site-packages\aqt\archives.py", line 447, in _get_archives_base
    if extensions_xml_text:
       ^^^^^^^^^^^^^^^^^^^
UnboundLocalError: cannot access local variable 'extensions_xml_text' where it is not associated with a value
ERROR   : aqtinstall(aqt) v3.1.21 on Python 3.12.6 [CPython MSC v.1940 64 bit (AMD64)]
Working dir: `D:\`
Arguments: `['C:\\Users\\Vladimir\\AppData\\Local\\Programs\\Python\\Python312\\Scripts\\aqt', 'install-example', '--outputdir', 'D:\\Qt2', 'windows', '6.8.0']` Host: `uname_result(system='Windows', node='MAIN-PC', release='11', version='10.0.22631', machine='AMD64')`
===========================PLEASE FILE A BUG REPORT===========================
You have discovered a bug in aqt.
Please file a bug report at https://github.com/miurahr/aqtinstall/issues
Please remember to include a copy of this program's output in your report.

Code of Conduct

• I agree to follow this project's Code of Conduct

[miurahr]

Thank you for the report.
I checked the code and the variable extensions_xml_text can be undefined when exception is occurred.

aqtinstall/aqt/archives.py

Lines 440 to 447 in 5ee98ef

	extensions_xml_url = posixpath.join(extensions_target_folder, "Updates.xml")
	# The extension may or may not exist for this version and arch.
	try:
	extensions_xml_text = self._download_update_xml(extensions_xml_url, True)
	except ArchiveDownloadError:
	# In case _download_update_xml ignores the hash and tries to get the url.
	pass
	if extensions_xml_text:

[miurahr]

The change of the chunk is by #852