Python has a great documentation section called “what’s new in Python” that discusses new features added in each version of Python. I recently read through all of them and learned several new tricks! From now on, I’ll be sure to read these each time a new version of Python is released.

Invalid numbers

One fun lesson: “01” is not a valid number in Python.

>>> (00, 01, 10, 11)
  File "<stdin>", line 1
    (00, 01, 10, 11)
SyntaxError: invalid token

Why? Python previously treated numbers starting with 0 as octal. As of Python 3, such numbers must now be prefixed with 0o, as in 0o31. In order to avoid subtle bugs, integers other than 0 are no longer allowed to start with 0 or -0.


Unpacking support has been improved multiple times over the past several releases. The following now works nicely.

>>> (a, *rest, b) = range(5)
>>> a
>>> rest
[1, 2, 3]
>>> b


>>> x
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
NameError: name 'x' is not defined
>>> exec("x = 5")
>>> x

JavaScript’s eval function, known primarily for horrifying security-minded programmers the world over, has a Python equivalent! “This function supports dynamic execution of Python code.” Read more in the docs, then forget that this exists.


Taking a slice of a generator, like range, can return another generator. Cool!

>>> range(0, 100, 2)[0:5]
range(0, 10, 2)

yield from expressions allow deferring to other generators within a generator.

>>> def g(x):
...     yield from range(x, 0, -1)
...     yield from range(x)
>>> list(g(5))
[5, 4, 3, 2, 1, 0, 1, 2, 3, 4]


The list of Python modules is also remarkably short and worth skimming. Modules that I was at most vaguely aware of, and inspired by the list to investigate more, include: