first: The function you always missed in Python
first is a MIT licensed Python package with a simple function that returns
the first true value from an iterable, or
None if there is none. If you need
more power, you can also supply a predicate whose result will be returned iff
I’m using the term “true” consistently with Python docs for
all()— it means that the value evaluates to true like:
[None]. But not:
A simple example first:
>> from first import first >> first([0, None, False, , (), 42]) 42
However, it’s especially useful for dealing with regular expressions in
import re from first import first re1 = re.compile('b(.*)') re2 = re.compile('a(.*)') m = first(regexp.match('abc') for regexp in [re1, re2]) if not m: print('no match!') elif m.re is re1: print('re1', m.group(1)) elif m.re is re2: print('re2', m.group(1))
The optional predicate gives you even more power. If you want to return the square of the first even number from a list, just do the following:
>>> from first import first >>> first([1, 1, 3, 4, 5], lambda x: (x ** 2) if (x % 2) == 0 else False) 16
The package consists of one module consisting of one function:
from first import first first(iterable, pred=None)
This function returns the first element of
iterable that is true if
None. If there is no true element,
None is returned.
If a callable is supplied in
pred, the result of
returned, if the result it true.
first has no dependencies and should work with any Python available. Of course, it works with the awesome Python 3 everybody should be using.
The idea for first goes back to a discussion I had with Łukasz Langa about
re example above is painful in Python. We figured such a function
is missing Python, however it’s rather unlikely we’d get it in and even if, it
wouldn’t get in before 3.4 anyway, which is years away as of yours truly is
So I decided to release it as a package for now. If it proves popular enough, it may even make it into Python’s stdlib in the end.