New in Python: Underscores in Numeric Literals

Python 3.6 added some interesting new features. The one that we will be looking at in this article comes from PEP 515: Underscores in Numeric Literals. As the name of the PEP implies, this basically gives you the ability to write long numbers with underscores where the comma normally would be. In other words, 1000000 can now be written as 1_000_000. Let’s take a look at some simple examples:

>>> 1_234_567
>>> '{:_}'.format(1234567)

The first example just shows how Python interprets a large number with underscores in it. The second example demonstrates that we can now give Python a string formatter, the “_” (underscore), in place of a comma. The results speak for themselves.

The numeric literals that include underscores behave the same way as normal numeric literals when doing calculations:

>>> 120_000 + 30_000
>>> 120_000 - 30_000

The Python documentation and the PEP also mention that you can use the underscores after any base specifier. Here are a couple of examples taken from the PEP and the documentation:

>>> flags = 0b_0011_1111_0100_1110
>>> flags
>>> 0x_FF_FF_FF_FF
>>> flags = int('0b_1111_0000', 2)
>>> flags

There are some notes about the underscore that need to be mentioned:

  • You can only use one consecutive underscore and it has to be between digits and after any base specifier
  • Leading and trailing underscores are not allowed

This is kind of a fun new feature in Python. While I personally don’t have any use cases for this in my current job, hopefully you will have one at yours.

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