在python 3.x中的for循环中，对象是否更改为不可变的？

Question

In my code pasted bellow (which is python 3 code) I expected the for loop to change the original objects (ie I expected NSTEPx to have been changed by the for loop). Since lists and arrays are mutable I should have edited the object by referring to it by the variable "data". However, after this code was run, and I called NSTEPx, it was not changed. Can someone explain why this is? I come from a background of C++ and the idea of mutable and immutable objects is something that I am only recently understanding the nuances of, or so I thought.

Here is the code:

NSTEPx = np.array(NSTEPx)
TIMEx = np.array(TIMEx)
TEMPx = np.array(TEMPx)
PRESSx = np.array(PRESSx)
Etotx = np.array(Etotx)
EKtotx = np.array(EKtotx)
EPtotx = np.array(EPtotx)
VOLUMEx = np.array(VOLUMEx)
alldata = [NSTEPx,TIMEx,TEMPx, PRESSx, Etotx, EKtotx, EPtotx]
for data in alldata:
    temp = data[1001:-1]
    data = np.insert(data,0,temp)
    data = np.delete(data,np.s_[1001:-1])

Answer 1

In your loop, data refers to an array (some object). The object referred to is mutable. The variable data can be changed as well to refer to something else, but that won't change what's in alldata (values that refer to objects) or the variables whose contents you implicitly copied to construct alldata . Hence, all you change is a local variable (implicitly copied from alldata ) to refer to a newly created array. Any other referring values are unchanged and still refer to the old array.

Answer 2

Python has no assignment! data = value is strictly a binding operation, not an assignment. This is really different then in eg C++

A Python variable is like a label, or a yellow sticky note: you can put it on something or move it to something else; it does not ( never ) change the thing (object) it is one. The =-operator does move the label; it "binds" it. Although we usually say assign , it is really not the assign of C. (Where it is basically is a memory address)

To change a value is Python, you need a method: aLabel.do_update() , will (typically) change self , the object itself. Note aList[....] is a method!

So, to change you data: change it (sec). Do not put a other label on it, nor put the existing label on other data!

Hope this explains you question