python - 为什么在表达式字段中不允许生成器中未加括号的元组？

Question

# why is the following invalid
x = (k, v for k, v in some_dict.items())

# but if we wrap the expression part in parentheses it works
x = ((k, v) for k, v in some_dict.items())

查看文档后，我找不到有关此问题的任何信息。在不允许语法的范围内，什么可能导致解析器混淆？这看起来很奇怪，因为尽管如此，更复杂的语法也能正常工作:

# k, v somehow confuses the parser but this doesn't???
x = ('%s:%s:%s' % (k, v, k) for k, v in some_dict.items())

如果真的有歧义。为什么我们也不需要将 %s:%s:%s % (k, v, k) 也用括号括起来？

Answer 1

看x = (k, v for k, v in some_dict.items()):

x = (k, v for k, v in some_dict.items())
x = ((k, v) for k, v in some_dict.items())
x = (k, (v for k, v in some_dict.items()))

需要括号来消除歧义。

x = ('%s:%s:%s' % (k, v, k) for k, v in some_dict.items()) 也需要括号:

x = ('%s:%s:%s' % k, v, k for k, v in some_dict.items())
x = ('%s:%s:%s' % k, (v, k) for k, v in some_dict.items())
x = ('%s:%s:%s' % (k, v, k) for k, v in some_dict.items())

碰巧你已经有足够的括号来解决那里的歧义，使其能够以预期的方式运行。