python一行函数定义
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python one line function definition
提问by guthrie
This must be simple, but as an only occasional python user, fighting some syntax. This works:
这一定很简单，但作为一个偶尔的 python 用户，与一些语法作斗争。这有效：
def perms (xs):
for x in itertools.permutations(xs): yield list(x)
But this won't parse:
但这不会解析：
def perms (xs): for x in itertools.permutations(xs): yield list(x)
Is there some restriction on the one-line function syntax? The body definition (for...) can be either two or one line by itself, and the def: can be one or two lines with a simple body, but combining the two fails. Is there a syntax rule that excludes this?
对单行函数语法有什么限制吗？主体定义 (for...) 本身可以是两行或一行，而 def: 可以是一两行并带有一个简单的主体，但将两者结合起来会失败。是否有排除此的语法规则？
采纳答案by Lennart Regebro
Yes, there are restrictions. No, you can't do that. Simply put, you can skip one line feed but not two. :-)
是的，有限制。不，你不能那样做。简而言之，您可以跳过一个换行符，但不能跳过两个。:-)
See http://docs.python.org/2/reference/compound_stmts.html
见http://docs.python.org/2/reference/compound_stmts.html
The reason for this is that it would allow you to do
这样做的原因是它可以让你做
if test1: if test2: print x
else:
print y
Which is ambiguous.
这是模棱两可的。
回答by Sean Vieira
If you musthave one line just make it a lambda:
如果您必须有一行，只需将其设为lambda：
perms = lambda xs: (list(x) for x in itertools.permutations(xs))
Quite often, when you have a short forloop for generating data you can replace it with either list comprehension or a generator expression for approximately the same legibility in slightly less space.
很多时候，当你有一个for用于生成数据的短循环时，你可以用列表理解或生成器表达式替换它，以在稍微更少的空间内获得大致相同的易读性。
回答by Supot Sawangpiriyakij
def perms (xs):
定义烫发（xs）：
for x in itertools.permutations(xs): yield list(x)
for x in itertools.permutations(xs): yield list(x)
You can use exec()to help this problem
你可以exec()用来帮助解决这个问题
exec('def perms (xs):\n for x in itertools.permutations(xs):\n yield list(x)\n')
beware to insert indented spacing or chr(9) after \n
注意在 \n 之后插入缩进的间距或 chr(9)
Example for if Python in one line
如果 Python 在一行中的示例
for i in range(10):
if (i==1):
print(i)
exec('for i in range(10)\n if (i==1):\n print(i)\n')
This is My project on GitHubto use exec to run Python program in interactive console mode
这是我在 GitHub上使用 exec 在交互式控制台模式下运行 Python 程序的项目
*note multiple line exec run only when end with '\n'
*注意多行 exec 仅在以 '\n' 结尾时运行
