Why is time conversion between epoch seconds and string changing time by 1 calendar year? - python-3.x

Question

I am using the time module of python3 to convert time between seconds and formatted string. Python functions used to generate string are localtime and strftime. To generate the time in seconds, I use string splicing followed by mktime. As I call these repeatedly on each result, only the year changes, always incrementing the seconds by a full year.
Code used is as below:
import time
def time_string(t):
#t is second obtained by time.mktime((yr, mn, dy, hr, mn, sec, 0, 0, 0))
time_struct = time.localtime(t)
time_string = time.strftime("%Y-%m-%d %H:%M:%S", time_struct)
return time_string
def string_time(t_string):
#t_string has format '2020-01-31 08:23:35'
yr = int(t_string[:4])
mn = int(t_string[5:7])
dy = int(t_string[8:10])
hr = int(t_string[11:13])
mn = int(t_string[14:16])
se = int(t_string[17:])
t=int(time.mktime((yr, mn, dy, hr, mn, se, 0, 0, 0)))
return t
t = int(time.mktime((2020, 3, 19, 18, 15, 20, 0, 0, 0)))
print (t)
for x in range(5):
t_st = time_string(t)
print(t_st)
t = string_time(t_st)
print(t)
sys.exit("stopping..")
The results I get from above code execution is as follows:
1584621920
2020-03-19 18:15:20
1616157920
2021-03-19 18:15:20
1647693920
2022-03-19 18:15:20
1679229920
2023-03-19 18:15:20
1710852320
2024-03-19 18:15:20
1742388320
SystemExit: stopping..
What am I doing wrong? Why does this happen?
What is a better way of converting time-string to seconds?

Answer 1

I do not get the purpose of the question, so what you're actually trying to do, however if you have a string of a time, and you want to have the seconds of it, try using datetime.timestamp() instead of a time-string-splicing...
Your code is increasing in the year by one beacuse in your method string_time(t_string) you set the variable mn twice! One time at mn = int(t_string[5:7]) and once at mn = int(t_string[14:16]) which will result in a month of 15 which will adapt the year by 1 year and 3 month which will result in the one year for you

Answer 2

Found time.strptime to solve the problem of converting back from string using the right formatters. The following code eliminated the need to do string splicing
def string_time(t_string):
#t_string has format '2020-01-31 08:23:35'
t_struct = time.strptime(t_string,"%Y-%m-%d %H:%M:%S")
t = int(time.mktime(t_struct))
return t
Korbinian had already found the error in my code. Is there a reason why I should use the datetime module instead of the date module?