Comment 1 for bug 812845

This is why pydoc says for me;

    class EnvironmentVariableFixture(fixtures.fixture.Fixture)
     | Isolate a specific environment variable.
     |
     | Method resolution order:
     | EnvironmentVariableFixture
     | fixtures.fixture.Fixture
     | __builtin__.object
     |
     | Methods defined here:
     |
     | __init__(self, varname, newvalue=None)
     | Create an EnvironmentVariableFixture.
     |
     | :param varname: the name of the variable to isolate.
     | :param newvalue: A value to set the variable to. If None, the variable
     | will be deleted.
     |
     | During setup the variable will be deleted or assigned the requested
     | value, and this will be restored in cleanUp.
     |

That seems pretty clear to me. Was it unclear? Or did you go from 'README' -> source code without looking at the API docs ?