python变量在使用前可以不赋值即使用_关于python：在赋值之前引用的局部变量..有时候...
>>> from riverwarn import get_river>>> mississippi = 'http://water.weather.gov/ahps2/river.php?wfo=jan&wfoid=18743&riverid=203833&pt%5B%5D=all&allpoints=143846%2C142736%2C143816%2C143998%2C145144%2C14...
