Understanding pytz process ... Naive, Aware, UTC, then any timezone?

Question

I'm still wrapping my head on the process of taking a naive datetime, shifting to the correct timezone then UTC. From there we can shift to different timezones.
Is my understanding correct?
I notated Ken's code for the pytz challenge below. Hope this helps.
```python
Use pytz and datetime
take date and time in MY timezone
return in 6 different timezones using format string (fmt = '%Y-%m-%d %H:%M:%S %Z%z')
from datetime import datetime
import pytz
Create list of different timezones which can be iterated through.
OTHER_TIMEZONES = [
    pytz.timezone('US/Eastern'),
    pytz.timezone('Pacific/Auckland'),
    pytz.timezone('Asia/Calcutta'),
    pytz.timezone('UTC'),
    pytz.timezone('Europe/Paris'),
    pytz.timezone('Africa/Khartoum')
]
fmt = '%Y-%m-%d %H:%M:%S %Z%z' # format datetime object
while True: # run until condition is False (break)
    dateinput = input("When is your meeting? Please use MM/DD/YYYY HH:MM format.  ") # Ask user for specific date format and assign to dateinput variable
    try:
        localdate = datetime.strptime(dateinput, '%m/%d/%Y %H:%M') # assign local date and format in date object from a string (dateinput) # why can't this take a 'fmt' variable?
    except ValueError: # an invalid user inputted date format will return this error statement
        print(f"{dateinput} doesn't seem to be a valid date & time.")
    else:
        localdate = pytz.timezone('US/Pacific').localize(localdate) # transforming naive time (localdate) to aware and setting to timezone 'Pacific' 
        utcdate = localdate.astimezone(pytz.utc) # difficult for me to understand this step. Shifting localdate to UTC time and assigning to utc_date
    output = [] # empty list to store results which will be printed
    for timezone in OTHER_TIMEZONES: # loop to iterate through OTHER_TIMEZONES
        output.append(utc_date.astimezone(timezone)) # take utc_date, shift to each timezone in OTHER_TIMEZONES list, add result to output list 
    for appointment in output: # loop for printing results stored in output
        print(appointment.strftime(fmt)) # format datetime object using formating from above then print
    break # stop program (end While loop)
```

Chris Freeman · Accepted Answer

Hey @justlevy (https://teamtreehouse.com/justlevy) , Yes, you have the gist. One big reason to go to UTC first is to work around problems with localtime (http://pytz.sourceforge.net/#problems-with-localtime). Nicely documented code.
Code feedback: flow of the code could be simplified to:
```python
while True: # run until condition is False (break)
    dateinput = input("When is your meeting? Please use MM/DD/YYYY HH:MM format.  ") # Ask user for specific date format and assign to dateinput variable
    try:
        localdate = datetime.strptime(dateinput, '%m/%d/%Y %H:%M') # assign local date and format in date object from a string (dateinput) # why can't this take a 'fmt' variable?
        break # end While loop if finished with it
    except ValueError: # an invalid user inputted date format will return this error statement
        print(f"{dateinput} doesn't seem to be a valid date & time.")
none of the following needs to be within the while loop or the try/except/else block
localdate = pytz.timezone('US/Pacific').localize(localdate) # transforming naive time (localdate) to aware and setting to timezone 'Pacific' 
utcdate = localdate.astimezone(pytz.utc) # difficult for me to understand this step. Shifting localdate to UTC time and assigning to utc_date
output = [] # empty list to store results which will be printed
for timezone in OTHERTIMEZONES: # loop to iterate through OTHERTIMEZONES
    output.append(utcdate.astimezone(timezone)) # take utcdate, shift to each timezone in OTHER_TIMEZONES list, add result to output list 
for appointment in output: # loop for printing results stored in output
    print(appointment.strftime(fmt)) # format datetime object using formating from above then print
```

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justlevy

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Understanding pytz process ... Naive, Aware, UTC, then any timezone?

1 Answer

Chris Freeman

Chris Freeman

justlevy

justlevy