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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def replace_braces(s, env):
 """Makes tox substitutions to s, with respect to environment env. Example ------- "echo andy passed no posargs" Note: first "{env:USER:}" is replaced with os.environ.get("USER", ""), the "{posargs:andy}" is replaced with "andy" (since no posargs were passed). """

    def replace(m):
        return _replace_match(m, env)
    for _ in range(DEPTH):
        s = re.sub(r"{[^{}]*}", replace, s)
    return s