Unfortunately I have encountered another problem.
I have installed python 2.7.5 with pyenv install 2.7.5 and then pyenv rehash
Now if I type python2.7 I get

pyenv: python2.7: command not found
The `python2.7' command exists in these Python versions:
2.7.5

I think this message should appear if there are others pythonx.y or pythonx version and the command is ambiguous but I have only one python version.
If I set pyenv local 2.7.5 then python2 or python2.7will start python correctly.

Am I missing something? Is possible to set the default pythonx version?