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Sunday, August 19, 2012

Running pep8 and pylint programatically

Having tools like pep8 and pylint are great, especially given the huge amount of dynamism involved in Python - which results in many opportunities to shooting yourself in the foot. Sometimes however you want to invoke these tools in more specialized ways, for example only on the files which changed since the last commit. Here is how you can do this from a python script and capture their output for later post-processing (maybe you want merge the output from both tools, or maybe you want to show only the lines which changed since the last commit, etc):

import pep8
  sys.stdout = StringIO()
  pep8_checker = pep8.StyleGuide(config_file=config, format='pylint')
  pep8_checker.check_files(paths=[ ...path to files/dirs to check... ])
  output = sys.stdout.getvalue()
  sys.stdout = sys.__stdout__

from pylint.lint import Run
from pylint.reporters.text import ParseableTextReporter

reporter = ParseableTextReporter()
result = StringIO()
Run(['--rcfile=pylint.config'] + [ ...files.., ], reporter=reporter, exit=False)
output = result.getvalue()

It is recommended that you use pylint/pep8 installed trough pip/easy_install rather than the Linux distribution repositories, since they are known to contain outdated software. You can check for this via code like the following:

if pkg_resources.get_distribution('pep8').parsed_version < parse_version('1.3.3'):
    logging.error('pep8 too old. At least version 1.3.3 is required')
if pkg_resources.get_distribution('pylint').parsed_version < parse_version('0.25.1'):
    logging.error('pylint too old. At least version 0.25.1 is required')

Finally, if you have to use an old version of pep8, the code needs to be modified to the following (however, this older version probably won't be of much use and will most likely annoy you - you should really try to use an up-to-date version - for example you could isolate this version using virtualenv):

result = []
import pep8
pep8.message = lambda msg: result.append(msg)
for code_dir in [ ...files or dirs... ]:


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