Is there any Pythonic or compact way to write the following if statement:
if head is None and tail is None:
print("Test")
Something like:
if (head and tail) is None:
4 Answers
If both head and tail are custom class instances (like Node() or similar) without a length or boolean value, then just use:
if not (head or tail):
This won't work if ether head or tail could be objects other than None with a false-y value (False, numeric 0, empty containers, etc.).
Otherwise, you are stuck with the explicit tests. There is no "English grammar" shortcut in boolean logic.
answered Dec 2, 2016 at 13:42
Martijn Pieters
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3 Comments
Moinuddin Quadri
Note, it will check value is not truthy (not just for
None value)
Kirill Bulygin
if not (head or tail) (or if not head and not tail)
Martijn Pieters
@KirillBulygin: I need more caffeine today.
if head is None and tail is None:
print("Test")
is clear and efficient. And if either head or tail can possibly take false-ish values apart from None but you only want "Test" to be printed when they're both None then what you've written is safer than
if not (head or tail):
print("Test")
A more compact version (than your code) which is still both safe & efficient is
if head is None is tail:
print("Test")
head is None is tail is actually equivalent to (head is None) and (None is tail). But I think it's a little less readable than your original version.
BTW, (head and tail) is None is valid Python syntax, but it's not recommended, since it doesn't do what you might at first expect it do:
from itertools import product
print('head, tail, head and tail, result')
for head, tail in product((None, 0, 1), repeat=2):
a = head and tail
print('{!s:>4} {!s:>4} {!s:>4} {!s:>5}'.format(head, tail, a, a is None))
output
head, tail, head and tail, result
None None None True
None 0 None True
None 1 None True
0 None 0 False
0 0 0 False
0 1 0 False
1 None None True
1 0 0 False
1 1 1 False
Comments
Your code is just about as Pythonic as it can be.
When it comes to these things, The Zen of Python is helpful in remembering that sometimes straightforward is the best option.
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
etc...
Comments
By the way, descriptions like (head and tail) is None are not allowed in programming for the same reason why (a and b) = 0 is not allowed in mathematics (to force each statement to have only one, canonical form; "There should be one obvious way to do each thing" is also an explicit Python motto).
2 Comments
PM 2Ring
What do you mean?
(head and tail) is None is perfectly valid in Python, but it doesn't do what one might expect it to do. :)Kirill Bulygin
I certainly mean
(head and tail) is None written with the same intent as (a and b) = 0.
'').if not head and not tail:headortailpossibly take on any other false-ish value?andshort-circuits, so the 2nd test will not be performed if the 1st one fails, i.e., ifheadisn'tNone. So your code is already quite efficient.