Lazy import cache

This is a pure Python file with no dependencies so it can be used in setup.py.

sage.misc.lazy_import_cache.get_cache_file()

Return the canonical filename for caching names of lazily imported modules.

EXAMPLES:

sage: from sage.misc.lazy_import_cache import get_cache_file
sage: get_cache_file()
'...-lazy_import_cache.pickle'
sage: get_cache_file().startswith(DOT_SAGE)
True
sage: 'cache' in get_cache_file()
True

It should not matter whether DOT_SAGE ends with a slash:

sage: OLD = DOT_SAGE
sage: sage.misc.lazy_import_cache.DOT_SAGE = '/tmp'
sage: get_cache_file().startswith('/tmp/')
True
sage: sage.misc.lazy_import_cache.DOT_SAGE = OLD