pipenv doesn't find correct python version on $PATH without pyenv

This is related to https://github.com/pypa/pipenv/issues/729 but I think I’ve found a different cause. When multiple versions of python 3 are installed on $PATH and pyenv is not available, then pipenv will only look at /usr/bin/python3 and not more explicit versions of python3 like /usr/bin/python3.6 even if python_version declares 3.6 as the target.

We’re using pipenv on our build server (jenkins) and haven’t quite figured out how to get pyenv working with jenkins pipelines yet.

Describe your environment

1. OS Type: Ubuntu 16.04
2. Python versions:

jenkins@jenkin:~/workspace$ /usr/bin/python3 --version
Python 3.5.2
jenkins@jenkins:~/workspace$ /usr/bin/python3.5 --version
Python 3.5.2
jenkins@jenkins:~/workspace$ /usr/bin/python3.6 --version
Python 3.6.3

1. Pipenv version: 9.0.3

Expected result

Virtualenv should be created using /usr/bin/python3.6 if it’s available on $PATH

Actual result

$ pipenv install --dev --three --verbose
Creating a virtualenv for this project…
Using /usr/bin/python3 to create virtualenv…
⠋Running virtualenv with interpreter /usr/bin/python3
Using base prefix '/usr'
New python executable in /var/lib/jenkins/.local/share/virtualenvs/venvnamehere/bin/python3
Also creating executable in /var/lib/jenkins/.local/share/virtualenvsvenvnamehere/bin/python
Installing setuptools, pip, wheel...done.

Virtualenv location: /var/lib/jenkins/.local/share/virtualenvs/venvnamehere

Warning: Your Pipfile requires python_version 3.6, but you are using 3.5.2 (/var/lib/j/.local/share/v/r/bin/python)

Files

Pipfile:

[[source]]

url = "https://pypi.python.org/simple"
verify_ssl = true
name = "pypi"


[dev-packages]

"flake8" = "*"
isort = "*"
werkzeug = "*"
pyopenssl = "*"
factory-boy = "<3.0,>=2.9"
"flake8-isort" = "*"
"flake8-builtins" = "*"
"flake8-comprehensions" = "*"
ipdb = "*"
responses = "*"


[packages]

django = ">=1.11.0,<2.0.0"
wagtail = "<1.14,>=1.13"
dj-database-url = "*"
gunicorn = "*"
"psycopg2" = "*"
whitenoise = "*"
raven = "*"
django-extensions = "*"
xmltodict = "*"
django-cloudinary-storage = "*"
newrelic = "*"
pygments = "<2.3.0,>=2.2.0"
django-fsm = "<3.0,>=2.5"
django-debug-toolbar = "*"


[requires]

python_version = "3.6"

[uranusjr]

The current rule works like this (if pyenv is not present):

1. --three is essentially a shorthand for --python=3 (and --two is --python=2).
2. If --python=X is specified, look for python{X} in PATH (if X looks like a version number).
3. Otherwise, if requires.python_version = Y look for python{Y} in PATH.
4. Otherwise use whatever Python Pipenv is on (sys.executable).

The logic is relatively straightforward by itself IMO, but not really what users would expect.

[jarshwah]

I think having --three and --python and requires.python_version all being independent confusing. Would a docs update to the requires.python_version or --three be welcome to explain the precedence and actual behaviour?