import os.path
import sys

from flask import current_app

def format_fname(value):
    # If the value is not an absolute path, the it is a builtin or
    # a relative file (thus a project file).
    if not os.path.isabs(value):
        if value.startswith(('{', '<')):
            return value
        if value.startswith('.' + os.path.sep):
            return value
        return '.' + os.path.sep + value

    # If the file is absolute and within the project root handle it as
    # a project file
    if value.startswith(current_app.root_path):
        return "." + value[len(current_app.root_path):]

    # Loop through sys.path to find the longest match and return
    # the relative path from there.
    paths = sys.path
    prefix = None
    prefix_len = 0
    for path in sys.path:
        new_prefix = os.path.commonprefix([path, value])
        if len(new_prefix) > prefix_len:
            prefix = new_prefix
            prefix_len = len(prefix)

    if not prefix.endswith(os.path.sep):
        prefix_len -= 1
    path = value[prefix_len:]
    return '<%s>' % path

Add a format_fname function which translates a absolute filename to a filename relative to the sys.path or relative to the project root
Add a format_fname function which translates a absolute filename to a filename relative to the sys.path or relative to the project root