python strings vs enum and how they are represented in memory level

Question

zoo.py
from main import animal

def getAnimal(animal)
    1) if animal == animal.tiger:
    or
    2) if animal == "animal"

and

main.py
import Zoo        
Class animal
    tiger = "tiger"
    bear  = "bear"

1) get = Zoo.getAnimal(animal.tiger)
or
2) get = Zoo.getAnimal("tiger"):

The above is extremely basic example but what is the "best" convention of performing the above code?

I was told it is better to do it via 1) approach because "strange things happen due to how python uses pointers."

Whats happening in terms of at memory level when the above codes are executed?

If I remember correctly, each memory addr gets ascii value of char for the conseq allocated memory address for strings?

Is it the same when string is now being referenced as an object that of animal.tiger?

Or are there no differences at all?

Qiau · Accepted Answer · 2013-09-02 18:20:05Z

2

If the compiler doesn't optimize the code (i.e. it's more complex than your example) #2 will allocate an anonymous string with another pointer.

But since == do string compare it will work even if it is two different strings (in memory).

In your example the compiler will most likely optimize the code to be the same:

>>> class animal:
...  tiger = "tiger"
...  bear = "bear"
...
>>> animal.tiger
'tiger'
>>> id(animal.tiger)
140052399801616
>>> id('tiger')
140052399801616
>>>

EDIT: Added example of user input where string memory location differ:

>>> id(animal.tiger)
140052399801616
>>> a=raw_input()
tiger
>>> id(a)
140052399801664
>>> a==animal.tiger
True
>>> a is animal.tiger
False

(use is to compare objects in memory as above)

edited Sep 2, 2013 at 18:20

answered Sep 2, 2013 at 18:08

Qiau

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4 Comments

nneonneo Over a year ago

Normally, they will actually be the same as they are both constant interned strings. However, if you got the input e.g. from a user, they would not be the same object.

ealeon Over a year ago

@nneonneo what do you mean by having an input from user being a diff object?

nneonneo Over a year ago

@ealeon: See Qiau's edit. Basically, dynamically-generated strings will generally have memory addresses separate from constant (interned) strings, at least in CPython (the most popular implementation).

ealeon Over a year ago

so the answer is there is no difference?

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