"Blockchain" on Python. Created using lessons by Oleg Molchanov (but code here is slightly improved and minified).

blockchain.py

import json as j, hashlib, os

def chinteg():
    res = []
    for f in [str(i) for i in sorted([int(ii) for ii in os.listdir('./blocks/')])][1:]:
        h = j.load(fi:=open('./blocks/'+f, 'r'))['hash']; fi.close()
        with open('./blocks/'+str(int(f)-1), 'rb') as fp: h2 =  hashlib.md5(fp.read()).hexdigest()
        res.append((int(f)-1, h2 == h))
    return res

def wbl(data: dict):
    fp = sorted([int(ii) for ii in os.listdir('./blocks/')])[-1]
    with open('./blocks/'+str(fp), 'rb') as f: data['hash'] =  hashlib.md5(f.read()).hexdigest()
    with open('./blocks/'+str(fp+1), 'w') as f: j.dump(data, f, ensure_ascii=False, indent=4)

def main():
    if not os.path.exists('./blocks/1'):
        if not os.path.exists('./blocks'): os.mkdir('./blocks')
        with open('1', 'w') as w: j.dump({}, w)
    # chech integrity of blockchain
    print(chinteg())
    # write block
    wbl({'name': 'aaa', 'id': 'bbb'})

if __name__ == "__main__": main()