使用setuptools（pip）时如何打印警告和错误

Question

I am using setuptools to package code such that it can be easily installed using

cd project_name && pip install .

During the setup process, I want to warn the user about pre-existing config files and print some post install instructions on the system. For example

/etc/project_name/project.conf exists. Not copying default config file.

I have tried to use print and logging.warning() but still the warnings don't appear when installing using pip. I have a feeling I am missing something obvious.

We are trying to support 3.0 > python >= 2.6 on Redhat family >= el6 and Ubuntu >= 14.04LTS

Answer 1

If you take a look at the pip source, in the function responsible for running the setup script, call_subprocess ( source here ), it says:

def call_subprocess(cmd, show_stdout=True, cwd=None, ...
    ...
    # The obvious thing that affects output is the show_stdout=
    # kwarg. show_stdout=True means, let the subprocess write directly to our
    # stdout. Even though it is nominally the default, it is almost never used
    # inside pip (and should not be used in new code without a very good
    # reason); as of 2016-02-22 it is only used in a few places inside the VCS
    # wrapper code. Ideally we should get rid of it entirely, because it
    # creates a lot of complexity here for a rarely used feature.
    #
    # Most places in pip set show_stdout=False. What this means is:
    # - We connect the child stdout to a pipe, which we read.
    # - By default, we hide the output but show a spinner -- unless the
    #   subprocess exits with an error, in which case we show the output.
    # - If the --verbose option was passed (= loglevel is DEBUG), then we show
    #   the output unconditionally. (But in this case we don't want to show
    #   the output a second time if it turns out that there was an error.)

In short, you can see the output only if:

• your setup exits with an error, or
• user calls pip with -v , the verbose flag