django1/django/utils/_os.py

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from os.path import join, normcase, abspath, sep
def safe_join(base, *paths):
"""
Joins one or more path components to the base path component intelligently.
Returns a normalized, absolute version of the final path.
The final path must be located inside of the base path component (otherwise
a ValueError is raised).
"""
# We need to use normcase to ensure we don't false-negative on case
# insensitive operating systems (like Windows).
final_path = normcase(abspath(join(base, *paths)))
base_path = normcase(abspath(base))
base_path_len = len(base_path)
# Ensure final_path starts with base_path and that the next character after
# the final path is os.sep (or nothing, in which case final_path must be
# equal to base_path).
if not final_path.startswith(base_path) \
or final_path[base_path_len:base_path_len+1] not in ('', sep):
raise ValueError('the joined path is located outside of the base path'
' component')
return final_path