Question

Is there a way to either:

• Always have -t enabled by default (warn about inconsistent tab usage)
• Be able to enable it programmatically on startup (eg. in a sitecustomize.py module)

It would need to work for embedded Python too (so aliasing python or similar solutions will be of no use). Use of sitecustomize.py allows us to hook into embedded Python instances, so this seems like a good place for it.

I thought the warnings module would provide a way to turn this warning on but I don’t see anything.

For reference:

usage: python [option] ... [-c cmd | -m mod | file | -] [arg] ...
Options and arguments (and corresponding environment variables):
...
-t     : issue warnings about inconsistent tab usage (-tt: issue errors)
...

Any suggestions on how this might be done?

Thanks.

Answer 1

The only solution I was able to come to involves import hooks. While this is somewhat beyond what I’d hoped to have to do, I felt it was a good excuse for me to learn how they work.

This solution doesn’t check for “inconsistent whitespace” it just checks for tabs, but it would be easy to extend.

Here is the result:

import sys
import imp
import warnings


class TabCheckImporter(object):

    """Finder and loader class for checking for the presence of tabs

    """

    def find_module(self, fullname, path=None):
        """Module finding method

        """
        # Save the path so we know where to look in load_module
        self.path = path
        return self

    def load_module(self, name):
        """Module loading method.

        """
        # Check if it was already imported
        module = sys.modules.get(name)
        if module is not None:
            return module

        # Find the module and check for tabs
        file_, pathname, description = imp.find_module(name, self.path)
        try:
            content = file_.read()
            tab = content.find("\t")
            if tab > -1:
                lineno = content[:tab].count("\n") + 1
                warnings.warn_explicit(
                        "module '{0}' contains a tab character".format(name),
                        ImportWarning,
                        pathname,
                        lineno)
        except Exception as e:
            warnings.warn("Module '{0}' could not be checked".format(name),
                          ImportWarning)

        # Import the module
        try:
            module = imp.load_module(name, file_, pathname, description)
        finally:
            if file_:
                file_.close()

        sys.modules[name] = module
        return module


# Register the hook
sys.meta_path = (sys.meta_path or []) + [TabCheckImporter()]

# Enable ImportWarnings
warnings.simplefilter("always", ImportWarning)

Importing this file (replacing ->| with a literal tab):

# File: test_tabbed.py
if True:
->| print "This line starts with a tab"

Yields this output:

$ python -c 'import hook; import test_normal; import test_tabbed;'
test_tabbed.py:3: ImportWarning: module 'test_tabbed' contains a tab character
  print "This line starts with a tab"