I need some feedback ... I wrote that code a while ago and can't read it anymore.

From: https://py.checkio.org/mission/find-sequence/solve/

def checkio(matrix):
    count = 0;
    digits = []
    # create set of symbols called digits
    for array in matrix:
        for elem in array:
            if elem not in digits:
                digits.append(elem)
    #check for horizontal lines
    horiz = find4(matrix, digits)
    #transpose matrix to use same method again
    transposedMatrix = transpose(matrix)
    #check for vertical lines
    vert = find4(transposedMatrix, digits)
    #check for diagonal lines
    stringBox = []
    stringBox2 = []
    stringBox3 = []
    diag = findDiagonal(matrix, digits, stringBox, stringBox2)
    diagT = findDiagonal(transposedMatrix, digits, stringBox, stringBox2)
    return horiz or vert or diag or diagT

def transpose(matrix):
    #stackoverflow transposed this
    new_matrix = [*zip(*matrix)]
    return new_matrix

def find4(matrix, digits):
    count = 0
    for symbol in digits:
        for row in matrix:
            for vector in row:
                if vector == symbol:
                    count += 1
                    if count == 4:
                        return True
                else:
                    count = 0
            count = 0  
    return False

def findDiagonal(matrix, digits, stringBox, stringBox2):
    length = len(matrix)
    box1 = []
    for item in digits:
        for elem in matrix:
            for e in elem:
                if e == item:
                    box1.append(elem.index(e))
    box2 = []
    resultBox = []
    length_subset(length, box2, stringBox, stringBox2)
    anotherString = toString(box1)
    #print(stringBox2)
    for elemString in stringBox2:
        elemString2 = str(box1)
        #print('start')
        print(elemString)      #TEST
        print(anotherString)   #TEST
        diag = seq_in_seq2(elemString,anotherString)
        elemStringR = elemString[::-1]
        #diagR = seq_in_seq2(elemStringR,anotherString)
        resultBox.append(diag)
        #resultBox.append(diagR)
    return True in resultBox
def seq_in_seq2(subseq, seq):
    if subseq in seq:
        return True
        print('TRUE')
    else:
        #print('FALSE')
        return False    
def seq_in_seq(subseq, seq):
     #print(subseq)         TEST
     #print(seq)
     while subseq[0] in seq:
         index = seq.index(subseq[0])
         #print(subseq)
         #print(seq)
         if subseq == seq[index:index + len(subseq)]:
             return True
         else:
             # 5432 is a False Negative in Assert Diagonal
             return 0
     else:
         return False
def length_subset(length, result, stringBox, stringBox2):
    if length < 3:
        flatten_me(result, stringBox2)
        return stringBox2
    else:
        newString = []
        newString.append(length)
        length2 = length - 1
        newString.append(length2)
        length3 = length2 - 1
        newString.append(length3)
        length4 = length3 - 1
        newString.append(length4)
        str1 = ''.join(str(e) for e in newString)
        result.append(str1)
        length_subset(length - 1, result, stringBox, stringBox2)
def flatten_me(listt, stringBox2):
    ans = []
    for elem in listt:
        if (elem.__class__ is list):
            for e in elem:
                if (e.__class__ is list):
                    for f in e:
                        if (f.__class__ is list):
                            stringBox2.append((f))
                        else:
                            stringBox2.append((f))                            
                else:
                    stringBox2.append((e))
        else:
            stringBox2.append(elem)
    return ans
def toString(myList):
    str1 = ''.join(str(e) for e in myList)
    return str1
def findDiagonal2():
    return False
'''
Test 11/12 (5x5)
False Positive 4321
This matrix is 6x6
011110
000000
440000
000021
443212  here
254345

test12/12
your result: false:
right result: true
2365628374
6959768516
6826193664
5832387464
2314512569
5487558495 eight
9799599812 eight
5174834188 eight
5332614388 eight
4814588747
'''
if __name__ == '__main__':
    #These "asserts" using only for self-checking and not necessary for auto-testing
    assert checkio([
        [1, 2, 1, 1],
        [1, 1, 4, 1],
        [1, 3, 1, 6],
        [1, 7, 2, 5]
    ]) == True, "Vertical"
    assert checkio([
        [7, 1, 4, 1],
        [1, 2, 5, 2],
        [3, 4, 1, 3],
        [1, 1, 8, 1]
    ]) == False, "Nothing here"
    assert checkio([
        [2, 1, 1, 6, 1],
        [1, 3, 2, 1, 1],
        [4, 1, 1, 3, 1],
        [5, 5, 5, 5, 5],
        [1, 1, 3, 1, 1]
    ]) == True, "Long Horizontal"
    assert checkio([
        [7, 1, 1, 8, 1, 1],
        [1, 1, 7, 3, 1, 5],
        [2, 3, 1, 2, 5, 1],
        [1, 1, 1, 5, 1, 4],
        [4, 6, 5, 1, 3, 1],
        [1, 1, 9, 1, 2, 1]
    ]) == True, "Diagonal"