python - a=[1,2,3,4,5]，b=a和b=a[:]，有区别么？

Answer 1

You call it

b.append(6)
print (a, b)

You can see the difference:

• The former passes the reference

• The latter is a copy

Answer 2

• b=a 會讓 b 參考到 a Reference object

• a[:] 會製造一個 a 的副本, 所以 b=a[:] 會讓 b 參考到這個副本, 也就是說 b 跟 a Now refer to different objects, but these two objects are equal ( not the same but equivalent )

This is why on the surface there seems to be no difference between the two, but if it is the former, we have changed b 或 a Both will be affected because they refer to the same object, but the latter does not affect each other because they refer to different objects. . @hsfzxjy's example is to point this out, and you can learn the difference by doing experiments.

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Questions I answered: Python-QA

Answer 3

Python has a function called id that can get the address of an object. It will be clear if you print it out. Direct = is reference assignment, referencing the original object; and [:] is re-derivation, which will generate a new object

a=[1,2,3,4,5]
b=a
c=a[:]
print id(a),id(b),id(c)