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Problem saving datetime to file and reading it back for a calculation

Thanks for the response.

I must have spent hours looking on-line for a method to treat datetime
variables yet not one site mentioned the "pickle" module you indicatged.  I
did, however solve my problem.  It may be a kluge but it seems to work.

I learned that I cannot use print() to display the value of datetime but
once I saved it to a file, I could see it.  If I used "d3 = d2.isoformat" it
could be sent to a file with a write statement.  Apparently, it gives a
write/read format and places a T between the date and time as a separator. 

In trying to read it back into the program and work the calculation, I had
to replace the T with a space and some formatting. It all worked.

d2 =
d2i = d2.isoformat()

with open("TimeDate.txt", 'r') as infile:
     for BottleInfo in infile: # loop to find each line in the file for that
       BottleInfo = BottleInfo.strip()

       if ((BottleInfo[0:3]== "LBD")):
            BottleData = BottleInfo[0:43].strip()

BottleDataA = BottleData[4:14].strip()
BottleDataB = BottleData[16:30].strip()
BottleDataC = BottleDataA + " " + BottleDataB
print("BottleDataC = <" + BottleDataC + ">")
# I guess I could have searched for the "T" and replaced it.            
d1 = BottleDataC

import datetime
dto = datetime.datetime.strptime(d1, '%Y-%m-%d %H:%M:%S.%f')
dti = dto.isoformat()

HoursDiff = int((d2-dto).total_seconds()/3600)
print("HoursDiff = " + str(HoursDiff))

TimeDateInfo=open("TimeDate.txt", "a") 
TimeDateInfo.write("{0:>5} {1:>25} {2:>5}\n".format (LBD, d2i, HoursDiff))

# ===========================================

Granted, there may be other ways to do this but I actually enjoy the
Still, I would like to see other methods.

-----Original Message-----
From: Dieter Maurer <dieter at> 
Sent: Sunday, October 11, 2020 12:48 PM
To: Steve <Gronicus at SGA.Ninja>
Subject: Re: Problem saving datetime to file and reading it back for a

Steve wrote at 2020-10-10 18:17 -0400:
>I would like to use the line:
>HoursDiff = int((d2-d1).total_seconds()/3600) to determine the 
>difference in hours between two timedate entries.
>The variable d2 is from
>and d1 is read from a text file.
>I can save d2 to the file only if I convert it to string and, at a later
>date, it gets read back in as d1 as string.   The variable d1 as string
>not work in the HoursDiff statement.

Python's "pickle" module provides support for storing (most) objects to
files and read them back.