python 评估打印结果之谜。评估（'3+4' + '6.5'）

Question

我不明白下面代码的结果。谁能解释一下？

x = eval('3+4' + '6.5')
print(x)
=> 49.5

x = eval('3+4' + '6.5')
print(x)
=> 49.5

y = eval('3'+'4' + '5.5')
print(y)
=> 345.5

z = eval('3+1' + '1.2')
print(z)
=> 14.2