Python variable assignment and IF statement

Question

Hello,

Sorry if this is Python 101 but I don't even know what to search for to get the answer. I come from a PHP background and would like to know if there's a way to do this in Python.

In PHP you can kill 2 birds with one stone like this:

Instead of:

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

I can do this:

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

You check to see if getData() exists AND if it does, you assign it to a variable in one statement.

I wanted to know if there's a way to do this in Python? So instead of doing this:

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

avoid writing request.GET.get('q') twice.

Thanks, g

Answer 1

Probably not exactly what you were thinking, but...

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

this?

Answer 2

See my 8-year-old recipe here for just this task.

Answer 3

Well, this would be one way

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

A briefer (but not superior, due to the call to print of nothing) way would be

print request.GET.get('q') or '',

Answer 4

q = request.GET.get('q')
if q:
    print q
else:
    # q is None
    ...

There's no way of doing assignment and conditionals in one go...

Answer 5

If get() throws an exception when it's not there, you could do

try:
   q = request.GET.get('q')
   print q
except :
   pass

Answer 6

A variation on Alex's answer:

class DataHolder:
    def __init__(self, value=None, attr_name='value'):
        self._attr_name = attr_name
        self.set(value)
    def __call__(self, value):
        return self.set(value)
    def set(self, value):
        setattr(self, self._attr_name, value)
        return value
    def get(self):
        return getattr(self, self._attr_name)
save_data = DataHolder()

Usage:

if save_data(get_input()):
    print save_data.value

or if you prefer an alternative interface:

if save_data.set(get_input()):
    print save_data.get()

I would find this helpful to test a series of regular expressions in an if-elif-elif-elif etc construct, as in this SO question:

import re

input = u'test bar 123'
save_match = DataHolder(attr_name='match')
if save_match(re.search('foo (\d+)', input)):
    print "Foo"
    print save_match.match.group(1)
elif save_match(re.search('bar (\d+)', input)):
    print "Bar"
    print save_match.match.group(1)
elif save_match(re.search('baz (\d+)', input)):
    print "Baz"
    print save_match.match.group(1)

Answer 7

config_hash = {}
tmp_dir = ([config_hash[x]  for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir
config_hash["tmp_dir"] = "cat"
tmp_dir = ([config_hash[x]  for x in ["tmp_dir"] if config_hash.has_key(x)] or ["tmp"])[0]
print tmp_dir