Python - some useful small functions

# find substring within a string
def find_between(s, first, last):
    try:
        start = s.index(first) + len(first)
        end = s.index(last, start)
        return s[start:end]
    except ValueError:
        return ""

# find index of certain charactor
def find(str, ch):
    for i, ltr in enumerate(str):
        if ltr == ch:
            yield i

# reformat epoch_time to YYYY-mm-dd
def format_date(data):
    if data == None or data == 'null' or find_between(data, "(", ")") == '':
        return ''    
    else:
        epoch_time = int(find_between(data,"(",")"))
        if epoch_time < 0 and epoch_time >= -1262304000:
            data = datetime(1970, 1, 1) + timedelta(seconds=epoch_time)
        else:
            if epoch_time >= 0 and epoch_time <= 2145916800:
                data = datetime.utcfromtimestamp(epoch_time)
            else:
                if epoch_time < -1262304000:
                    data = datetime(1970, 1, 1) + timedelta(milliseconds=epoch_time)
                else:
                    if epoch_time > 2145916800:
                        data = datetime.utcfromtimestamp(epoch_time / 1000)

        data = f"{data:%Y-%m-%d}"        
        return data