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Python-04| Fundamental data types vs immutability
- 2. What is Immutable? Once we created an object then we cannot change that object. Immutable means unchangeable. All fundamental data types (int, float, complex, bool, str) is immutable. Uses for internal reason(memory utilization). x = 10 x = 20 x 10 20 Only variable’s reference changed and the previous value is left unchanged
- 3. Representation of variable’s reference a 10 20 1723196320 1723196480 b Id is built in func to get the address of an identifier. Reuse of object for b
- 4. Advantage or disadvantage ? Some may think that if we keep on changing value of x then we have to make new object for each ‘x’, so there may be a chance of memory wastage, performance may down. But don’t think like that because it is really an advantage feature of Python. Because if a object is already available then it uses the existing object suppose we have thousands of variable with same object x1 = 10 x2 = 10 x3 = 10 xn = 10 10 x2 x1 x3 x5x4 x6 x7 xn Only one object is shared with n number of variables. No need to create separate object. This makes memory utilization and better performance
- 5. Example Hyd v1 v2 v4 v3 Agra Now v3 changes the city to Agra, then only the link will change from “Hyd” to “Agra” the object will not be deleted as it is still shared by v1, v2, and v4 49316480 49317984
- 6. ‘is’ operator Is operator tests if two variables point the same object, not if two variables have the same value. Lists are mutable i.e., changeable Different address though x and y have same value. But lists are mutable i.e., both x and y points to different object. But if you assign (y = x) then both points to the same object. Returns True if both points to same object
- 7. Use of ‘is’ operator instead of id to check variable references Only one True object is created with 3 references pointing towards the single object
- 8. What if I take x = 257? It should be True Different address, means 2 different object for same x = 257 257x y 257 58040688 58041344
- 9. Cont... Internally, reusing of same object is available from 0 to 256 only(most precisely -5 to 256), because this range is most commonly used by programs. In programs we generally use x = 10 or x = 20 etc. There are very rare case when we use more than 256 values. More than 256 is very rare case to use so there is no need to use the same object. If do so there may be a chance of memory wastage.
- 10. Cont... What happens internally is at the time of python interpreter starts than before execution of program, interpreter creates 0 to 256 integer objects. i.e., objects with content 0 to 256 created at the time of interpreter starts. a = 10 interpreter checks that: Is already object for content 10 is available or not? Obviously object with content 10 is already created at the beginning . Then ‘a’ just points to already created object. Interpreter doesn’t create the new object from 0 to 256. If a = 500 will create the new object as object with content 500 will not be found.
- 11. Why the range is 0 to 256 only? Ques: Why Python interpreter doesn’t make more objects i.e., more than 256 lets say rages from -1 crore to 1 crore? Ans: As we have discussed that 0 to 256 objects created at the time of interpreter starts as 0 to 256 is most commonly used range. Lets suppose if python creates object from -1 crore to 1 crore i.e., 2 crore objects at time of interpreter starts than python will take more and more time to start. May be one day after . So python start up will become very costly. we mostly use 2 or 3 objects, so for the sake of 3 or 4 objects, creating 2 crore objects at the beginning is stupidness and instead of advantage many problem may occur.
- 12. Immutability for bool In Boolean case, it always reuse the existing object It never create the objects at run time, because only two objects(True & False) are required to create These two objects created at the time of interpreter starts. Same address i.e., same object is shared
- 13. Immutability with str It always create the object at run time. It doesn’t create object at time of interpreter starts because there may be infinite strings literals a user can choose. Then for how many and for which literal interpreter makes object at beginning, this prediction is impossible. But still Python gave reuse of same object facility to str type also because most of the time we use same str literals. True shows same object is shared
- 14. Cont...
- 15. Immutability with float & complex Surprisingly reusability of same object is not with float and complex numbers.
- 16. Cont... If we talk about int only 0 to 256 values are in range of reusability the same object which is fixed. In case of bool only two value are there to hold the concept of reusability. But in terms of float or complex, can you tell how many values are there between in 0 and 1 only 0.1 0.01 0.11 0.101 infinite Then how python will make this much object at the beginning. At language level, float and complex assume to be immutable. 0.1 + 0.2j #complex also have floating values 0.11 + 0.101j 0.10 + 0.111j 0.01 + 0.9j ........infinite
- 17. Things to remember All fundamental data types are immutable. Immutable means unchangeable. ‘is’ operator test if both variable points to same object or not. Reusing the same object lies in following ranges: Int 0 to 256 Bool always Str always Float Never Complex Never In terms of str python create object at the run time not at the beginning as str value are infinite. Reusing of same object is not available. Every time a new object is created
- 18. Immutable? Class Immutable? Mutable? Int Float Complex Bool Str Bytes Bytearray Range List Tuple Set Frozenset Dictionary