为什么python不支持：while（s = f.readline（））？

Question

more example below:

 if (a = xyz() ) > abc: 

Really want to know why, is it kinds of bad smell ?

Note: I know the grammar, but I am asking why Python don't support such grammar as many other language( eg, c , java...) do supporting

Answer 1

From the python design FAQ :

The reason for not allowing assignment in Python expressions is a common, hard-to-find bug in those other languages, caused by this construct:

  if (x = 0) { // error handling } else { // code that only works for nonzero x } 

The error is a simple typo: x = 0, which assigns 0 to the variable x, was written while the comparison x == 0 is certainly what was intended.

As explained in the FAQ, most "use cases" for using assignment in an expression can be covered by using iterators instead.

Answer 2

Remember python philosophy : There should be one-- and preferably only one --obvious way to do it.
It doesn't sound obvious to me !
Also you may want to check this answer too :
why does python assignment not return a value