Python multiple nested ternary expression

Question

With the Python (2.7) ternary expression x if cond else y what is the logical order when evaluating multiple expressions of these nested in order: e.g.

1 if A else 2 if B else 3

Drawing out the truth table for this is appears this is evaluated as 1 if A else (2 if B else 3) rather than (1 if A else 2) if B else 3:

A      True  False
B                 
True      1      2
False     1      3

Could someone please explain why this is executed in this order, and possibly suggest some material that gives an intuition about why this is used/preferred?

This doesn't seem obvious when considering the ordering using the inline for statement:

>>>[(i, j, k) for i in range(1) for j in range(2) for k in range(3)]
[(0, 0, 0), (0, 0, 1), (0, 0, 2), (0, 1, 0), (0, 1, 1), (0, 1, 2)]

Answer 1

1 if A else 2 if B else 3 translates to this:

def myexpr(A, B):
    if A:
        return 1
    else:
        if B:
            return 2
        else:
            return 3

Your ternary expression can be interpreted with parentheses as follows:

(
 (1 if A) else (
                (2 if B) else 3
               )
)