Unable to resolve unindent issue in python

Question

I am new to python ,searched alot for the error but still unable to resolve the issue but i am getting the following error :IndentationError: unindent does not match any outer indentation level

class Solution:
    def numDecodings(self,name):
        print(name)
        return self.helper(s)

    def helper(self,sentence):
        print(sentence)

if __name__ == "__main__":
   s=Solution()
   s.numDecodings('2263')

Error:

File "decode.py", line 21
    def helper(self,sentence):
                             ^
IndentationError: unindent does not match any outer indentation level