Original Translation
35
while (line = readline(f)) { // do something with line }
36
where in Python you're forced to write this::
37
while True: line = f.readline() if not line: break ... # do something with line
38
The reason for not allowing assignment in Python expressions is a common, hard-to-find bug in those other languages, caused by this construct:
39
if (x = 0) { // error handling } else { // code that only works for nonzero x }
40
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.
á é í ó ú ç ñ ü ¿ ¡
41
Many alternatives have been proposed. Most are hacks that save some typing but use arbitrary or cryptic syntax or keywords, and fail the simple criterion for language change proposals: it should intuitively suggest the proper meaning to a human reader who has not yet been introduced to the construct.
42
An interesting phenomenon is that most experienced Python programmers recognize the ``while True`` idiom and don't seem to be missing the assignment in expression construct much; it's only newcomers who express a strong desire to add this to the language.
43
There's an alternative way of spelling this that seems attractive but is generally less robust than the "while True" solution::
44
line = f.readline() while line: ... # do something with line... line = f.readline()