rref of an augmented matrix without using numpy in python

main.py
def rref(matrix):
    lead = 0
    rowCount = len(matrix)
    columnCount = len(matrix[0])
    for r in range(rowCount):
        if lead >= columnCount:
            return
        i = r
        while matrix[i][lead] == 0:
            i += 1
            if i == rowCount:
                i = r
                lead += 1
                if columnCount == lead:
                    return
        matrix[i], matrix[r] = matrix[r], matrix[i]
        lv = matrix[r][lead]
        matrix[r] = [mrx / float(lv) for mrx in matrix[r]]
        for i in range(rowCount):
            if i != r:
                lv = matrix[i][lead]
                matrix[i] = [iv - lv*rv for rv,iv in zip(matrix[r],matrix[i])]
        lead += 1
    return matrix
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