Turn an indented block of text into a 'tree' view with unicode lines

treeify.py

#!/usr/bin/env python3
'''
Treeify takes a file (on stdin or passed as the first argument) and converts
it's indentation into a 'tree' representation. As an example:

    what
        is
        this
            thing
        that's
        happening

becomes the following "tree" structure:


    └ what
        ├ is
        ├ this
        │   └ thing
        ├ that's
        └ happening

Note that treeify requires all indentation to be done using spaces and only
accepts four spaces as one 'indentation level'.
'''

import fileinput


def count_indent(line):
    for idx, c in enumerate(line):
        if not c.isspace():
            return idx // 4
    return 0


def get_tree(lines, depth):
    level = list()
    while True:
        if len(lines) < 1:
            return level
        if not lines[0].strip():
            lines.pop(0)
            continue
        curdepth = count_indent(lines[0])
        if curdepth > depth:
            level.append(get_tree(lines, curdepth))
        elif curdepth == depth:
            level.append(lines.pop(0).strip())
        elif curdepth < depth:
            return level


def non_lists_exist(collection):
    for x in collection:
        if not isinstance(x, list):
            return True
    return False


def print_level(level, prefix=''):
    PARENT_CONTINUATION_PREFIX = '│   '
    NOPARENT_PREFIX = '    '
    ITEM_MARK = '├ '
    END_LEVEL = '└ '
    while True:
        if len(level) < 1:
            return
        cur = level[0]
        nxt = None
        if len(level) > 1:
            nxt = level[1]

        if isinstance(cur, list):
            if len(level) > 1:
                print_level(cur, '{}{}'.format(prefix,
                                               PARENT_CONTINUATION_PREFIX))
            else:
                print_level(cur, '{}{}'.format(prefix, NOPARENT_PREFIX))
        elif nxt is None:
            print('{}{}{}'.format(prefix, END_LEVEL, cur))
            return
        else:
            # Handle the case where there aren't any more strings at this level
            cur_prefix = END_LEVEL
            if non_lists_exist(level[1:]):
                cur_prefix = ITEM_MARK
            print('{}{}{}'.format(prefix, cur_prefix, cur))
        level.pop(0)


def main():
    docs_structure_lines = list()
    docs_structure_lines = [x for x in fileinput.input()]
    tree = get_tree(docs_structure_lines, 0)
    print_level(tree)


if __name__ == '__main__':
    main()