bug#34266: pypi importer cannot handle [ and ] correctly

[swedebugia]

$ ./pre-inst-env guix import pypi beaker

following redirection to `https://pypi.org/pypi/Beaker/json'...

Starting download of /tmp/guix-file.p15GJZ
From 
https://files.pythonhosted.org/packages/c2/21/b052b2fbfee3def06670923d5d34b0d353d4c278013e4a714c3fb663f150/Beaker-1.10.0.tar.gz...
 ...0.0.tar.gz  40KiB                 521KiB/s 00:00 
[##################] 100.0%
(package
  (name "python-beaker")
  (version "1.10.0")
  (source
    (origin
      (method url-fetch)
      (uri (pypi-uri "beaker" version))
      (sha256
        (base32
          "0l047yl3n9b3w7ba0wrqdb5fpww5y8pjy20kah2mlpr230lqjwk0"))))
  (build-system python-build-system)
  (propagated-inputs
    `(("python-[crypto]" ,#{python-\x5b;crypto\x5d;}#)
      ("python-[cryptography]"
       ,#{python-\x5b;cryptography\x5d;}#)
      ("python-[pycrypto]"
       ,#{python-\x5b;pycrypto\x5d;}#)
      ("python-[pycryptodome]"
       ,#{python-\x5b;pycryptodome\x5d;}#)
      ("python-[testsuite]"
       ,#{python-\x5b;testsuite\x5d;}#)
      ("python-coverage" ,python-coverage)
      ("python-cryptography" ,python-cryptography)
      ("python-cryptography" ,python-cryptography)
      ("python-funcsigs" ,python-funcsigs)
      ("python-memcached" ,python-memcached)
      ("python-mock" ,python-mock)
      ("python-nose" ,python-nose)
      ("python-pycrypto" ,python-pycrypto)
      ("python-pycryptodome" ,python-pycryptodome)
      ("python-pycryptodome" ,python-pycryptodome)
      ("python-pycryptopp" ,python-pycryptopp)
      ("python-pylibmc" ,python-pylibmc)
      ("python-pymongo" ,python-pymongo)
      ("python-redis" ,python-redis)
      ("python-sqlalchemy" ,python-sqlalchemy)
      ("python-webtest" ,python-webtest)))
  (home-page "https://beaker.readthedocs.io/";)
  (synopsis
    "A Session and Caching library with WSGI Middleware")
  (description
    "A Session and Caching library with WSGI Middleware")
  (license license:bsd-3))