CODEWITHSUNDEEP
pythonmemory-management
Abdelouahab Pp
Abdelouahab Pp

Reputation: 4440

will i assign values or use them directly in other variables?

if i've a program running on a server, which one will use more memory:

a = operation1()

b = operation2()

c = doOperation(a, b)

or directy:

a = doOperation(operation1(), operation2())

Edit:

1: i'm using CPython.

2: i'm asking this question because sometimes, i love readability in my code, so instead of writing looong sequences of operation, u just split them into variables.

Edit2:

here is the full code:

class Reset(BaseHandler):
@tornado.web.asynchronous
@tornado.gen.engine
def get(self, uri):
    uri = self.request.uri
    try:
        debut = time.time()
        tim = uri[7:]
        print tim
        cod = yield tornado.gen.Task(db.users.find_one, ({"reset.timr":tim})) # this is temporary variable
        code = cod[0]["reset"][-1]["code"] # this one too
        dat = simpleencode.decode(tim, code)
        now = datetime.datetime.now() # this one too
        temps = datetime.datetime.strptime(dat[:19], "%Y-%m-%d %H:%M:%S") # this one too
        valid = now - temps # what if i put them all here
        if valid.days < 2:
            print time.time() - debut # here time.time() has not been set to another variable, used directly
            self.render("reset.html")
        else:
            self.write("hohohohoo")
            self.finish()
    except (ValueError, TypeError, UnboundLocalError):
        self.write("pirate")
        self.finish()

as you can see there are variables that are only temporarly useful.

Upvotes: 1

Views: 64

Answers (2)

Martijn Pieters
Martijn Pieters

Reputation: 1121446

Provided doOperation() does not clear it's own references to the arguments passed in, or create more references to the arguments, until doOperation() completes, the two approaches are exactly the same.

The latter will use less memory once doOperation() completes, because by then the local variables of the function are cleaned up. In the first option, because a and b still hold references, the ref count does not drop to 0.

CPython uses reference counting to clean up any objects that are no longer used; once the reference count drops to 0 objects are automatically cleaned up.

If memory and readability are a concern, you can delete references explicitly:

a = operation1()
b = operation2()

c = doOperation(a, b)

del a, b

but remember that local variables inside a function are cleaned up automatically, so the following would also result in the a and b references being removed:

def foo():
    a = operation1()
    b = operation2()

    c = doOperation(a, b)

Upvotes: 2

Ned Batchelder
Ned Batchelder

Reputation: 375494

Memory occupied by values will only be reclaimed when the values are no longer referenced. Just looking at the examples you gave, it's impossible to tell when those values are no longer referenced, because we don't know what doOperation does.

One thing to keep in mind: assignment never copies values, so merely assigning a value to a name won't increase the memory use.

Also, unless you have an actual memory problem, don't worry about it. :)

Upvotes: 1

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