setting PIP_NO_CACHE_DIR=yes causes pip to crash

[njsmith]

~$ pip --version
pip 10.0.1 from /home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip (python 3.5)

~$ PIP_NO_CACHE_DIR=yes pip install
Exception:
Traceback (most recent call last):
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 228, in main
    status = self.run(options, args)
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/commands/install.py", line 241, in run
    with self._build_session(options) as session:
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 78, in _build_session
    if options.cache_dir else None
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/posixpath.py", line 89, in join
    genericpath._check_arg_types('join', a, *p)
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/genericpath.py", line 143, in _check_arg_types
    (funcname, s.__class__.__name__)) from None
TypeError: join() argument must be str or bytes, not 'int'

(Actually, it printed the exception twice: once in red text, and once in regular text.)

[pradyunsg]

How does it behave with 1 or 0?

[njsmith]

Same problem with 1, but 0 works ok:

~$ PIP_NO_CACHE_DIR=1 pip install
Exception:
Traceback (most recent call last):
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 228, in main
    status = self.run(options, args)
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/commands/install.py", line 241, in run
    with self._build_session(options) as session:
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 78, in _build_session
    if options.cache_dir else None
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/posixpath.py", line 89, in join
    genericpath._check_arg_types('join', a, *p)
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/genericpath.py", line 143, in _check_arg_types
    (funcname, s.__class__.__name__)) from None
TypeError: join() argument must be str or bytes, not 'int'
Traceback (most recent call last):
  File "/home/njs/.user-python3.5-64bit/bin/pip", line 11, in <module>
    sys.exit(main())
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/__init__.py", line 246, in main
    return command.main(cmd_args)
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 264, in main
    timeout=min(5, options.timeout)) as session:
  File "/home/njs/.user-python3.5-64bit/local/lib/python3.5/site-packages/pip/_internal/basecommand.py", line 78, in _build_session
    if options.cache_dir else None
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/posixpath.py", line 89, in join
    genericpath._check_arg_types('join', a, *p)
  File "/home/njs/.user-python3.5-64bit/lib/python3.5/genericpath.py", line 143, in _check_arg_types
    (funcname, s.__class__.__name__)) from None
TypeError: join() argument must be str or bytes, not 'int'

~$ PIP_NO_CACHE_DIR=0 pip install
ERROR: You must give at least one requirement to install (see "pip help install")

[jakirkham]

Appears to be the same as issue ( #2897 ).

[lietu]

The issue seems to be that something somewhere is badly messed up with this variable.

It seems when you set PIP_NO_CACHE_DIR to off/false it sets the "no cache dir" option on. This is obviously the wrong behavior.

This needs to be fixed: export PIP_NO_CACHE_DIR=true (or 1, on, etc.) must be equal to pip --no-cache-dir. Anything else is clearly broken functionality.

[pfmoore]

@lietu It's a pretty well known consequence of how pip's option parsing works (although when I checked the docs, I couldn't see anything explicitly noting it). I agree it's confusing - if you feel that strongly about it maybe you'd be willing to contribute a PR fixing it? (But be aware, it's not a simple fix - it's basically a limitation of the optparse parser that we use, the real fix is to switch to a more modern parser.) Or a doc fix noting the non-intuitive behaviour and explaining how to correctly set the value would be a useful interim fix.

[lietu]

Funny thing is that at this point if it's "well known", fixing it will break backwards compatibility with the plethora of custom scripts people have written with that setting. Basically the fix would include supporting the old behavior, and having a new flag that works better.

I.e. something like

pip --no-cache-dir
export PIP_NO_CACHE_DIR=off
pip --disable-cache
export PIP_DISABLE_CACHE=true

Should all be equal, with maybe the first two causing a warning saying something like "this functionality may be deprecated in the future over the --disable-cache and PIP_DISABLE_CACHE -options."