how to directly import now() from datetime.datetime submodule

Question

Background: I have a few tight loops in a Python program that are called repeatedly, which include the datetime.datetime.now() method, as well as the datetime.datetime.min and datetime.datetime.max attributes. For optimization, I would like to import them into the local namespace, avoiding the repeated, unnecessary module hierarchy name look-up, like so:

from datetime.datetime import now, min, max

However, Python complains:

Traceback (most recent call last):
  File "my_code.py", line 1, in <module>
    from datetime.datetime import now, min, max
ImportError: No module named datetime

Question: Why doesn't the above submodule import work?

Workaround: I can instead do this:

import datetime
dt_now = datetime.datetime.now
dt_min = datetime.datetime.min
dt_max = datetime.datetime.max

But, I'm curious why the more traditional approach does not work? Why can I not import methods and properties directly from the datetime.dateime submodule? ... And, is there any reason to avoid the above workaround (besides readability, outsmarting myself, etc.)?

Thanks!

Answer 1

datetime.datetime is not a submodule. datetime is a class within the datetime module. now is a method of that class. You can't use from...import... to import individual methods of a class. You can only use it to import individual modules from a package, or individual objects that exist at the top level of a module.

As for your workaround, if you want shorthand, I find it more readable to do this:

from datetime import datetime as dt
dt.now()
# you can also use dt.max, dt.min, etc.

If you really want to put those methods directly in local variables, then your workaround makes sense.