Add the --python option to the debug:resolve command

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Added
 
 - Added a new, more efficient dependency resolver.
+- Added the `--extras` and `--python` options to `debug:resolve` to help debug dependency resolution.
 
 
 ## [0.9.1] - 2018-05-18

poetry/console/commands/debug/resolve.py

@@ -12,6 +12,7 @@ class DebugResolveCommand(Command):
     debug:resolve
         { package?* : packages to resolve. }
         { --E|extras=* : Extras to activate for the dependency. }
+        { --python= : Python version(s) to use for resolution. }
     """
 
     _loggers = [
@@ -49,7 +50,8 @@ class DebugResolveCommand(Command):
                 self.poetry.package.name,
                 self.poetry.package.version
             )
-            package.python_versions = self.poetry.package.python_versions
+
+            package.python_versions = self.option('python') or self.poetry.package.python_versions
             for dep in dependencies:
                 package.requires.append(dep)