Getting the first non None value from list

Question

Given a list, is there a way to get the first non-None value? And, if so, what would be the pythonic way to do so?

For example, I have:

• a = objA.addr

Answer 1

first_true is an itertools recipe found in the Python 3 docs:

def first_true(iterable, default=False, pred=None):
    """Returns the first true value in the iterable.

    If no true value is found, returns *default*

    If *pred* is not None, returns the first item
    for which pred(item) is true.

    """
    # first_true([a,b,c], x) --> a or b or c or x
    # first_true([a,b], x, f) --> a if f(a) else b if f(b) else x
    return next(filter(pred, iterable), default)

One may choose to implement the latter recipe or import more_itertools, a library that ships with itertools recipes and more:

> pip install more_itertools

Use:

import more_itertools as mit

a = [None, None, None, 1, 2, 3, 4, 5]
mit.first_true(a, pred=lambda x: x is not None)
# 1

a = [None, None, None]
mit.first_true(a, default="All are None", pred=lambda x: x is not None)
# 'All are None'

---

Why use the predicate?

"First non-None" item is not the same as "first True" item, e.g. [None, None, 0] where 0 is the first non-None, but it is not the first True item. The predicate allows first_true to be useable, ensuring any first seen, non-None, falsey item in the iterable is still returned (e.g. 0, False) instead of the default.

a = [None, None, None, False]
mit.first_true(a, default="All are None", pred=lambda x: x is not None)
# 'False'