Subtraction of two datetime objects in Python:
- It is allowed to subtract one datetime object from another datetime object
- The resultant object from subtraction of two datetime objects is an object of type timedelta
Example:
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import datetime
d1 = datetime.datetime.now() d2 = datetime.datetime.now() x = d2-d1 print(type(x)) print(x) |
Output:
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<class 'datetime.timedelta'> 0:00:00.000008 |
- The subtraction operation of two datetime objects succeeds, if both the objects are naive objects, or both the objects are aware objects. i.e., Both the objects have their tzinfo as None
- If one datetime object is a naive object and another datetime object is an aware object then python raises an exception of type TypeError stating TypeError: can't subtract offset-naive and offset-aware datetimes.
Example:
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import datetime
# Time difference for pacific time pacificTimeDelta = datetime.timedelta(hours=-8)
# Create a PST timezone in instance tzPST = datetime.timezone(pacificTimeDelta, name="PST")
# create a datetime for 1 PM PST - 31Dec2017 - An aware Object OnePMyearEnd = datetime.datetime(2017,12,31,1,0,0,0,tzPST)
# create a dateobject for current time - without any timezone attached - A naive object todaysDate = datetime.datetime.now()
# Try subtracting the naive object from the aware object # This will raise a Type Error todaysDate = OnePMyearEnd - todaysDate
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Output:
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todaysDate = OnePMyearEnd - todaysDate TypeError: can't subtract offset-naive and offset-aware datetimes |
- If both the datetime objects are aware objects and each object is having a different time zone information – then both the time quantity of the objects are converted into UTC first and the subtraction is applied on the two UTC time quantities.
Example:
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import datetime
# Time difference for pacific time pacificTimeDelta = datetime.timedelta(hours=-8)
# Create a PST timezone in instance tzPST = datetime.timezone(pacificTimeDelta, name="PST")
# create a datetime for 1 PM PST - 31Dec2017 - An aware Object OnePMyearEndPST = datetime.datetime(2017,12,31,1,0,0,0,tzPST)
# Time difference for EST time nycTimeDelta = datetime.timedelta(hours=-8)
# Create a PST timezone in instance tzEST = datetime.timezone(nycTimeDelta, name="EST")
# create a datetime for 1 PM PST - 31Dec2017 - An aware Object TwoPMyearEndEST = datetime.datetime(2017,12,31,2,0,0,0,tzEST)
print(TwoPMyearEndEST-OnePMyearEndPST)
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Output:
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1:00:00 |