[Tutor] How to convert string to date time format?

[Steven D'Aprano]

On Fri, Jul 19, 2019 at 10:44:36PM -0400, C W wrote:
> Hello all,
> 
> I have a date time string that looks like the following.
> 
> 0    2015-07-01 00:01:44.538420-08:00
> 1    2015-07-01 00:27:58.717530-08:00
> 2    2017-07-01 07:07:48.391376-08:00

I assume that the leading number and spaces "0    " etc are NOT part of 
the strings.

 
> I have tried the following two different methods, both did not work.
> Method one: pandas
> import pandas as pd
> stamp = pd.to_datetime(my_string, format='%Y%m%d %H:%M:%S')
> 
> Method two: datetime package
> from datetime import datetime
> datetime.strptime(my_string, '%Y-%m-%d %H:%M:%S')
> 
> 
> Are both ways suppose to work?

Not unless the string format matches the actual string. You can't expect 
to convert a string unless it matches the format.


> Also, does it matter if there are decimals
> after seconds?

Of course it matters.

Did you read the error message? The single most important skill for a 
programmer is to READ THE ERROR MESSAGE and pay attention to what it 
tells you went wrong:

py> datetime.strptime('2015-07-01 00:01:44.538420-08:00', '%Y-%m-%d %H:%M:%S')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/_strptime.py", line 510, in _strptime_datetime
    tt, fraction = _strptime(data_string, format)
  File "/usr/local/lib/python3.5/_strptime.py", line 346, in _strptime
    data_string[found.end():])
ValueError: unconverted data remains: .538420-08:00


See how the error message tells you that it couldn't convert the string 
because there is data left over at the end. The first thing to do is 
handle the microseconds.

Googling gets the answer: use "%f" as the code for fractional seconds.

https://duckduckgo.com/?q=strptime+seconds+with+decimals


py> datetime.strptime('2015-07-01 00:01:44.538420-08:00', '%Y-%m-%d %H:%M:%S.%f')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/local/lib/python3.5/_strptime.py", line 510, in _strptime_datetime
    tt, fraction = _strptime(data_string, format)
  File "/usr/local/lib/python3.5/_strptime.py", line 346, in _strptime
    data_string[found.end():])
ValueError: unconverted data remains: -08:00


Now we're making progress! The error message has changed. Now you just 
need to decide what the "-08:00" part means, and change the format 
string appropriately.



-- 
Steve