运用循环求和（ sum operation in python)

1.for loop

 example 1: sum of 1+2+...+10

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>>> sum=0

>>> for x in [1,2,3,4,5,6,7,8,9,10]:

        sum=sum+x

>>> print(sum)

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example 2: sum of 1+2+...+100

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sum=0

for x in range (101):

   sum=sum+x

print(sum)

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