Python导入语句引发异常

Question

我有一些代码是这样的

try:
  import calvin.reasoning.rule_list
except:
  print "rule_list exception"

我把规则中的每一个导入语句都注释掉了_列表.py，看起来像这样

^{2}$

如果我删除rule_list的内容，我的程序运行，但是如果没有循环导入，python为什么会抛出异常呢？在

这是回溯

Traceback (most recent call last):
  File "/home/paul/projects/branchCalvin/Calvin/src/cscience/components/c_calibration.py", line 18, in <module>
    import calvin.reasoning.rule_list
  File "/home/paul/projects/branchCalvin/Calvin/src/calvin/reasoning/rule_list.py", line 37, in <module>
    import rules
  File "/home/paul/projects/branchCalvin/Calvin/src/calvin/reasoning/rules.py", line 32, in <module>
    import engine
  File "/home/paul/projects/branchCalvin/Calvin/src/calvin/reasoning/engine.py", line 33, in <module>
    import conclusions
  File "/home/paul/projects/branchCalvin/Calvin/src/calvin/reasoning/conclusions.py", line 31, in <module>
    import samples
  File "/home/paul/projects/branchCalvin/Calvin/src/calvin/reasoning/samples.py", line 30, in <module>
    from cscience import datastore
ImportError: cannot import name datastore
problem importing module components.c_calibration
(<type 'exceptions.ImportError'>, ImportError('cannot import name datastore',), <traceback object at 0x9ebc554>)