为什么一些简短形式的条件在python中有效，有些则不然？

Question

Take the example:

 a = "foo" if True else "bar"

This executes fine and without problems. now take:

print("foo") if True else print("bar")

This throws an error.

I assume the first one works like a ternary operator. Is there a way to write the second statement without resorting to the full length:

if True:
    print("foo")
else:
    print("bar")

Something akin to Perl's

print("foo") if True

Answer 1

1. All paths of a conditional expression , must be evaluatable.

2. In Python 2.7, print is a statement , not a function. So, it cannot be evaluated as an expression.

Since print statement violates point 2, it cannot be used. But you can do

print "foo" if True else "bar"

In Python 3.x, print is a function , so you can write as you mentioned in the question

print("foo") if True else print("bar")

Since print is a function in Python 3.x, the result of the function call will be the result of the evaluation of the function call expression. You can check this like this

print(print("foo") if True else print("bar"))
# foo
# None

print function doesn't explicitly return anything. So, by default, it returns None . The result of evaluating print("foo") is None .