Invalid dev dependency

• I am on the latest Poetry version.
• I have searched the issues of this repo and believe that this is not a duplicate.
• If an exception occurs when executing a command, I executed it again in debug mode (-vvv option).

• OS version and name: Ubuntu 18.04
• Poetry version: Poetry 0.11.5
• Link of a Gist with the contents of your pyproject.toml file: None

Issue

Doing the following:

git clone https://github.com/sdispater/poetry && cd poetry
poetry install

Poetry fails to install black 18.6b4 with this error using -vvv:

Installing dependencies from lock file


Package operations: 8 installs, 0 updates, 1 removal, 53 skipped

  - Skipping six (1.11.0) Already installed
  - Skipping atomicwrites (1.2.1) Already installed
  - Skipping attrs (18.2.0) Already installed
  - Skipping certifi (2018.8.24) Already installed
  - Skipping chardet (3.0.4) Already installed
  - Skipping colorama (0.3.9) Not needed for the current platform
  - Skipping idna (2.7) Already installed
  - Skipping markupsafe (1.0) Already installed
  - Skipping more-itertools (4.3.0) Already installed
  - Skipping pluggy (0.7.1) Already installed
  - Skipping py (1.6.0) Already installed
  - Skipping pyyaml (3.13) Already installed
  - Skipping tornado (5.1) Already installed
  - Skipping urllib3 (1.23) Already installed
  - Skipping appdirs (1.4.3) Already installed
  - Skipping aspy.yaml (1.1.1) Already installed
  - Skipping cached-property (1.5.1) Already installed
  - Skipping cfgv (1.1.0) Already installed
  - Skipping click (6.7) Already installed
  - Skipping coverage (4.5.1) Already installed
  - Skipping identify (1.1.5) Already installed
  - Skipping jinja2 (2.10) Already installed
  - Skipping livereload (2.5.2) Already installed
  - Skipping lockfile (0.12.2) Already installed
  - Skipping markdown (2.6.11) Already installed
  - Skipping msgpack (0.5.6) Already installed
  - Skipping nodeenv (1.3.2) Already installed
  - Skipping pastel (0.1.0) Already installed
  - Skipping pygments (2.2.0) Already installed
  - Skipping pylev (1.3.0) Already installed
  - Skipping pytest (3.8.0) Already installed
  - Skipping requests (2.19.1) Already installed
  - Skipping toml (0.9.6) Already installed
  - Skipping virtualenv (16.0.0) Already installed
  - Skipping webencodings (0.5.1) Already installed
  - Installing black (18.6b4)
                                                                                                
[VenvCommandError]                                                               
Command ['pip', 'install', '--no-deps', 'black==18.6b4'] errored with the following output:   
Collecting black==18.6b4                                                                      
  Could not find a version that satisfies the requirement black==18.6b4 (from versions: )     
No matching distribution found for black==18.6b4                                              
                                                                                                
Exception trace:
 /home/dimitris/.local/lib/python3.6/site-packages/cleo/application.py in run() at line 94
   status_code = self.do_run(input_, output_)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/console/application.py in do_run() at line 88
   return super(Application, self).do_run(i, o)
 /home/dimitris/.local/lib/python3.6/site-packages/cleo/application.py in do_run() at line 197
   status_code = command.run(input_, output_)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/console/commands/command.py in run() at line 77
   return super(BaseCommand, self).run(i, o)
 /home/dimitris/.local/lib/python3.6/site-packages/cleo/commands/base_command.py in run() at line 146
   status_code = self.execute(input_, output_)
 /home/dimitris/.local/lib/python3.6/site-packages/cleo/commands/command.py in execute() at line 107
   return self.handle()
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/console/commands/install.py in handle() at line 50
   return installer.run()
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/installer.py in run() at line 76
   self._do_install(local_repo)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/installer.py in _do_install() at line 286
   self._execute(op)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/installer.py in _execute() at line 294
   getattr(self, "_execute_{}".format(method))(operation)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/installer.py in _execute_install() at line 319
   self._installer.install(operation.package)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/pip_installer.py in install() at line 76
   self.run(*args)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/installation/pip_installer.py in run() at line 91
   return self._venv.run("pip", *args, **kwargs)
 /home/dimitris/.local/lib/python3.6/site-packages/poetry/utils/venv.py in run() at line 274
   raise VenvCommandError(e)

The issue is that pip2 doesn’t find the version 18.6b4

/usr/bin/pip2 install -U black==18.6b4                                                               
Collecting black==18.6b4
  Could not find a version that satisfies the requirement black==18.6b4 (from versions: )
No matching distribution found for black==18.6b4

Pip3 does find the version:

 /usr/bin/pip3 install -U black==18.6b4                                                             1 master
Collecting black==18.6b4
  Using cached https://files.pythonhosted.org/packages/4e/b5/575cdaabf1f98ebe50c0ee85b202fcce3b8df1f21d6ed02708bc539674c3/black-18.6b4-py36-none-any.whl
Collecting toml>=0.9.4 (from black==18.6b4)
  Using cached https://files.pythonhosted.org/packages/c7/19/76c3cb84949a0593767b32b9be83a604d8a68c3580ff5d0ee64856b39ade/toml-0.9.6-py2.py3-none-any.whl
Collecting attrs>=17.4.0 (from black==18.6b4)
  Using cached https://files.pythonhosted.org/packages/3a/e1/5f9023cc983f1a628a8c2fd051ad19e76ff7b142a0faf329336f9a62a514/attrs-18.2.0-py2.py3-none-any.whl
Collecting appdirs (from black==18.6b4)
  Using cached https://files.pythonhosted.org/packages/56/eb/810e700ed1349edde4cbdc1b2a21e28cdf115f9faf263f6bbf8447c1abf3/appdirs-1.4.3-py2.py3-none-any.whl
Collecting click>=6.5 (from black==18.6b4)
  Using cached https://files.pythonhosted.org/packages/34/c1/8806f99713ddb993c5366c362b2f908f18269f8d792aff1abfd700775a77/click-6.7-py2.py3-none-any.whl
Installing collected packages: toml, attrs, appdirs, click, black
Successfully installed appdirs-1.4.3 attrs-18.2.0 black-18.6b4 click-6.7 toml-0.9.6

[pmav99]

Black doesn’t have a stable release yet. You need to install it with:

poetry add --dev --allow-prereleases black

[M5oul]

Corresponding ticket in Black https://github.com/python/black/issues/517.