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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 caller_trace(back=0):
 """ Trace caller stack and save info into global dicts, which are printed automatically at the end of SCons execution. """

    global caller_bases, caller_dicts
    import traceback
    tb = traceback.extract_stack(limit=3+back)
    tb.reverse()
    callee = tb[1][:3]
    caller_bases[callee] = caller_bases.get(callee, 0) + 1
    for caller in tb[2:]:
        caller = callee + caller[:3]
        try:
            entry = caller_dicts[callee]
        except KeyError:
            caller_dicts[callee] = entry = {}
        entry[caller] = entry.get(caller, 0) + 1
        callee = caller