Added Python2/Python3 support

Separated Python file from vim script, added logic for selecting
available python interpreter compiled in vim.

ftplugin/python/pep8_fn.py

@@ -0,0 +1,58 @@
+"""
+Get pep8 output on current vim buffer using pep8.Checker object
+"""
+try:
+    import pep8
+except ImportError:
+    raise AssertionError('Error: pep8_fn.vim requires module pep8')
+
+import vim
+
+
+class VImPep8(object):
+    """Vim PEP8 checker"""
+
+    def __init__(self):
+        self.fname = vim.current.buffer.name
+        self.bufnr = vim.current.buffer.number
+        self.output = []
+        self.exclude_list = vim.eval("g:pep8_exclude")
+
+    def reporter(self, lnum, col, text, check):
+        """Custom reporter for checker report_error method"""
+        self.output.append([lnum, col, text])
+
+    def run(self):
+        """Run the checker"""
+        pep8.process_options(['-r', vim.current.buffer.name])
+        checker = pep8.Checker(vim.current.buffer.name)
+        checker.report_error = self.reporter
+        checker.check_all()
+        self.process_output()
+
+    def process_output(self):
+        """Transform checker output into quickfix list"""
+        vim.command('call setqflist([])')
+        qf_list = []
+        qf_dict = {}
+
+        for line in self.output:
+            skip = False
+            for exclude_pattern in self.exclude_list:
+                if exclude_pattern in line[2]:
+                    skip = True
+                    break
+            if skip:
+                continue
+            qf_dict['bufnr'] = self.bufnr
+            qf_dict['lnum'] = line[0]
+            qf_dict['col'] = line[1]
+            qf_dict['text'] = line[2]
+            qf_dict['type'] = line[2][0]
+            qf_list.append(qf_dict)
+            qf_dict = {}
+
+        self.output = []
+        vim.command('call setqflist(%s)' % str(qf_list))
+        if qf_list:
+            vim.command('copen')