sysconfig.py 文件源码

def expand_makefile_vars(s, vars):
    """Expand Makefile-style variables -- "${foo}" or "$(foo)" -- in
    'string' according to 'vars' (a dictionary mapping variable names to
    values).  Variables not present in 'vars' are silently expanded to the
    empty string.  The variable values in 'vars' should not contain further
    variable expansions; if 'vars' is the output of 'parse_makefile()',
    you're fine.  Returns a variable-expanded version of 's'.
    """

    # This algorithm does multiple expansion, so if vars['foo'] contains
    # "${bar}", it will expand ${foo} to ${bar}, and then expand
    # ${bar}... and so forth.  This is fine as long as 'vars' comes from
    # 'parse_makefile()', which takes care of such expansions eagerly,
    # according to make's variable expansion semantics.

    while 1:
        m = _findvar1_rx.search(s) or _findvar2_rx.search(s)
        if m:
            (beg, end) = m.span()
            s = s[0:beg] + vars.get(m.group(1)) + s[end:]
        else:
            break
    return s