Sometimes you have to insert a string into the middle of another string, like "C" into "ABDE" so it becomes "ABCDE".html
def insert(original, new, pos):
'''Inserts new inside original at pos.'''
return original[:pos] + new + original[pos:]
引自：http://twigstechtips.blogspot.com/2010/02/python-insert-string-into-another.html
python