CODEWITHSUNDEEP
pythonvariables
Dusk
Dusk

Reputation: 1877

Which way of using variables is more efficient in terms of speed, cpu, memory, etc in python?

Assume we have a function which wants to operate some actions on attribute z of objA. objA is a property of objB and objB is a property of objC etc... which of these two approaches is faster ? Is there any difference?

Approach 1: Using objC.objB.objA.zfor every statement in the function.

Approach 2: Assigning a local variable like x in function as:

x=objC.objB.objA.z

then operate on x, then assign the output to the preferable variable.

I know Approach 2 makes it easier in terms of writing the actual code but doesn't defining a new variable cost more memory? Which approach is more pythonic and is there any other (better) way to do things other than aforementioned approaches?

Upvotes: 1

Views: 104

Answers (2)

BrenBarn
BrenBarn

Reputation: 251365

Approach 2 will in general be quicker, although it may not be a noticeable difference unless it's in a tight loop.

Every time you do a.b.c.d, Python has to look up the values of those attributes, even if they don't change in between uses. If you create a variable x for that value once, then Python only has to look up the attributes once, saving time.

Doing x = a.b.c.d does not create a new object, so it doesn't use any memory. x will be a reference to the same object that a.b.c.d pointed to. However, because of this, you do need to be careful. Any operations that mutate x will affect the original object. For instance, if a.b.c.d is a list, and you do x = a.b.c.d, then x.append(1) will alter the value of the original a.b.c.d object. If this is what you want, great. If not, be sure to explicitly copy the value.

Upvotes: 4

jamylak
jamylak

Reputation: 133514

The 2nd one is more pythonic and it will also be faster if you are reusing objC.objB.objA.z many times because it avoids having to do those 4 lookups each time. It isn't costly to bind this value to x, Python simply uses the same reference to the object and will not copy it.

Upvotes: 2

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