python - 如何避免两次写入 request.GET.get() 以打印它？

Question

我来自 PHP 背景，想知道是否有办法在 Python 中做到这一点。

在 PHP 中，你可以像这样用一 block 石头杀死 2 只鸟:

代替:

if(getData()){
    $data = getData();
    echo $data;
}

我可以这样做:

if($data = getData()){
    echo $data;
}

您检查 getData() 是否存在，如果存在，则在一个语句中将其分配给一个变量。

我想知道是否有办法在 Python 中做到这一点？所以不要这样做:

if request.GET.get('q'):
    q = request.GET.get('q')
    print q

避免两次写request.GET.get('q')。

Answer 1

见我 8 年的食谱 here只为这个任务。

# In Python, you can't code "if x=foo():" -- assignment is a statement, thus
# you can't fit it into an expression, as needed for conditions of if and
# while statements, &c.  No problem, if you just structure your code around
# this.  But sometimes you're transliterating C, or Perl, or ..., and you'd
# like your transliteration to be structurally close to the original.
#
# No problem, again!  One tiny, simple utility class makes it easy...:

class DataHolder:
    def __init__(self, value=None): self.value = value
    def set(self, value): self.value = value; return value
    def get(self): return self.value
# optional but handy, if you use this a lot, either or both of:
setattr(__builtins__,'DataHolder',DataHolder)
setattr(__builtins__,'data',DataHolder())

# and now, assign-and-set to your heart's content: rather than Pythonic
while 1:
    line = file.readline()
    if not line: break
    process(line)
# or better in modern Python, but quite far from C-like idioms:
for line in file.xreadlines():
    process(line)
# you CAN have your C-like code-structure intact in transliteration:
while data.set(file.readline()):
    process(data.get())