Variables in Python are objects, abstracting addresses and memory. Variables can be understood as "pointers". Variables store the address of the value, not the variable itself.
For example: a = 2
The variable a actually stores the address of 2 in memory, not the value of 2.
With this understanding we look at some procedures:
1. It's easy to understand, a = 2, b = a, b is naturally equal to 2
2. a = 3, output 3, 2 is also easy to understand
3. According to the serial number 1 and serial number 2 to understand the output as [2], [2] is no problem
4. The output of serial number 4 is [3], [3] according to serial number 1 and serial number 2 to understand that what should be output here is [3], [2] right?
5. If you understand it according to serial number 4, the output here should be [4], [4], why did it become [4], [3] again?
The reason for the above results involves immutable data types and variable data types in Python
Immutable data types: integer int, float, string, and tuple
Variable data types: list list and dictionary dict
The essence of both depends on whether the data in memory is modified
Because a is an immutable data type, reallocate space when assigning a new value, and store the value to the new memory address to variable a. The original value 2 has not been changed, so the value 2 in the address saved in the b variable No change.
This can explain why the output of serial number 2 is 3, 2
Because a is a list, it is a variable data type, so the address of a has not changed. a [0] only changes the immutable data type saved in the list.
This can explain the output of serial number 3, because a and b save the list address 47349576, the content of this list changes, and the output of both a and b will change.
a = [4] means that the first address of the list saved by a is overwritten by the first address of list [4], and b is still the first address of the original list saved, that is, 47349576, so the output of sequence number 5 is not [4], [4].
note:
The list address of a = [3] and b = [3] are different, the same is only the address of immutable data type 3
