python字符串格式化：不使用两个列表的方法？

Question

使用以下代码：

a = ['foo', 'bar', 'doh', 'rae']

我想要字符串SUM(foo) AS foo, SUM(bar) AS bar, SUM(doh) AS doh, SUM(rae) AS rae。这有效：

尝试像'SUM(%s) AS %s' % ([x for x in a], [x for x in a])这样聪明的东西，但显然它没有用，并且使用两个列表推导感觉效率很低。

任何提示？

Answer 1

为什么不使用str.format method？

", ".join(['SUM({n}) AS {n}'.format(n=x) for x in a])
# Returns SUM(foo) AS foo, SUM(bar) AS bar, SUM(doh) AS doh, SUM(rae) AS rae

如果a是一个大型列表，您可能需要使用生成器，以避免首先在内存中创建整个列表，如GWW所指出的那样。

", ".join('SUM({n}) AS {n}'.format(n=x) for x in a)

Answer 2

你可以使用str.format函数在一个字符串中传递一个两次争论，类似：

s = ', '.join(['SUM({0}) AS {0}'.format(x) for x in a])

并且通过一个列表推导和连接操作，它可以产生所需的输出

'SUM(foo) AS foo, SUM(bar) AS bar, SUM(doh) AS doh, SUM(rae) AS rae'

问候！