[Python] Using Python dateutil, how to judge a timezone string is "valid" or not?

I am using the following code to do the UTC time to local time conversion:

def UTC_to_local(timezone_str, datetime_UTC):
"""
convert UTC datetime to local datetime. Input datetime is naive
"""
try:
from_zone = dateutil.tz.gettz('UTC')
to_zone = dateutil.tz.gettz(timezone_str)

datetime_UTC = datetime_UTC.replace(tzinfo=from_zone)

# Convert time zone
datetime_local = datetime_UTC.astimezone(to_zone)

except Exception as e:
raise

return datetime_local


If I gave the correct timezone_str (e.g., 'America/Chicago'), it works as expected. But even I give the unexpected timezone_str (e.g., 'America/Chicago1' or 'Americaerror/Chicago'), there is still no exception and it just returns different numbers! I think it's more reasonable to get an exception for an unexpected timezone string than just "making the best guess".

Furthermore, I have found(using IPYTHON):

In [171]: tz.gettz("America/Chicago")
Out[171]: tzfile('/usr/share/zoneinfo/America/Chicago')

In [172]: tz.gettz("America/Chicago1")
Out[172]: tzstr('America/Chicago1')

In [173]: tz.gettz("Americaerror/Chicago")
(None)

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