Matrix Diagonal Sum LeetCode solution in Python

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class Solution:
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    def diagonalSum(self, mat: List[List[int]]) -> int:
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        n = len(mat)
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        mid = n // 2
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        summation = 0
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        for i in range(n):
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            # primary diagonal
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            summation += mat[i][i]
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            # secondary diagonal
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            summation += mat[n - 1 - i][i]
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        if n % 2 == 1:
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            # remove center element (repeated) on odd side-length case
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            summation -= mat[mid][mid]
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        return summation