there is no inbuilt zfill but I use this zfl function

def zfl(s, width):
# Pads the provided string with leading 0's to suit the specified 'chrs' length
# Force # characters, fill with leading 0's
return '{:0>{w}}'.format(s, w=width)

This might be useful to you? Just pass the string and the string width you require.

When you use

for i in t:

i is not index, each item.

>>> for i in t:
...     print(i)
...
2019
10
11
3
40
8
686538
None

If you want to use index, do like following:

>>> for i, v in enumerate(t):
...     print("{} is {}".format(i,v))
...
0 is 2019
1 is 10
2 is 11
3 is 3
4 is 40
5 is 8
6 is 686538
7 is None

another way to create '191011034008'

>>> t = (2019, 10, 11, 3, 40, 8, 686538, None)
>>> "".join(map(lambda x: "%02d" % x, t[:6]))
'20191011034008'
>>> "".join(map(lambda x: "%02d" % x, t[:6]))[2:]
'191011034008'

note that:

1. %02d add leading zero when argument is lower than 10 otherwise (greater or equal 10) use itself. So year is still 4digit string.

2. This lambda does not expect that argument is None.

I tested this code at https://micropython.org/unicorn/

edited :

str.format method version:

"".join(map(lambda x: "{:02d}".format(x), t[:6]))[2:]

or

"".join(map(lambda x: "{0:02d}".format(x), t[:6]))[2:]

second example's 0 is parameter index. You can use parameter index if you want to specify it (ex: position mismatch between format-string and params, want to write same parameter multiple times...and so on) .

>>> print("arg 0: {0}, arg 2: {2}, arg 1: {1}, arg 0 again: {0}".format(1, 11, 111))
arg 0: 1, arg 2: 111, arg 1: 11, arg 0 again: 1