当我尝试进行字符串格式化时，出现了关键错误
In [9]: template = "%(key_1)s(%(key_2)s, %(key_3)s)"
In [10]: map_var = {"key_2": "some_value"}
In [11]: template % map_var
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
<ipython-input-11-b19f23cee642> in <module>()
----> 1 template % map_var
KeyError: 'key_1'
但是，我期望是一个字符串，
"%(key_1)s(some_value, %(key_3)s)"
如何获取此字符串？