bug#19761: python.el: improved hideshow mode support

[Carlos Pita <carlosjosepita@gmail.com>]

X-Debbugs-CC: galli.87@gmail.com
Tags: patch

I've found two issues with the current hs configuration:

1) The hs-block-start-regexp wants to anchor at the beginning of line.
At least, this doesn't behave well with hs-hide-level-recursive. Try
C-c @ C-l on the line after the class statement below. The problem is
that the point is not always at the beginning of line when the regexp
is evaluated by hs.

2) The hs-forward-sexp-func is python-nav-end-of-defun. This is fine
as far as the function is separated by a blank line from the code that
follows it. Otherwise the closed fold is joined with the line
immediately following it. Try C-c @ C-h on the nested def below. This
is easily fixed going one char back when the point is not left in an
empty line after python-nav-end-of-defun.

So after the changes the new hs configuration is:

  (add-to-list 'hs-special-modes-alist
               `(python-mode "\\s-*\\(?:def\\|class\\)\\>" nil "#"
                             ,(lambda (_arg)
                                (python-nav-end-of-defun)
                                (unless (python-info-current-line-empty-p)
                                  (backward-char)))
                             nil))

Here is the (real life) example mentioned above:

class PivotReader:

    def __init__(self, file, num_cols):
        self._pr_file = open(file) if type(file) is str else file
        self._pr_reader = csv.reader(self._pr_file)
        header = next(self._pr_reader)
        self._pr_cols = {col: i for i, col in enumerate(header)}
        self._pr_nums = [col in num_cols for col in header]
        self._pr_vals = None

    def next_row(self):
        try:
            self._pr_vals = next(self._pr_reader)
            return True
        except:
            return False

    def __enter__(self):
        return self

    def __exit__(self, type, value, tb):
        self._pr_file.close()

    def __getattr__(self, col):
        return self[col]

    def __getitem__(self, cols):
        def get(col):
            idx = self._pr_cols[col]
            val = self._pr_vals[idx]
            num = self._pr_nums[idx]
            return float(val) if num else val
        if type(cols) is str:
            return get(cols)
        else:
            return tuple(map(get, cols))