Case Analysis of Python Direct assignment, shallow copy and Deep copy

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This paper gives an example of Python direct assignment, shallow copy and deep copy. Share with you for your reference, the details are as follows:

Direct assignment: it is actually a reference (alias) to the object.

Copy: copies the parent object, not the internal child objects of the object.

Deep copy (deepcopy): the deepcopy method of the copy module that completely copies the parent object and its children.

Dictionary shallow copy instance

Example

> a = {1: [1min2 a.copy () > a, b () > > a, b ({1: [1rem 2jue 3]}, {1: [1m 2jue 3]}) > > a [1] .append (4) > > a, b ({1: [1pr 2je 3,4]}, {1: [1pm 2jue 3,4]})

Deep copy requires the introduction of the copy module:

Example

> > import copy > c = copy.deepcopy (a) > > a, c ({1: [1,2,3,4]}, {1: [1,2,3,4]}) > > a [1] .append (5) > > a, c ({1: [1,2,3,4,5]}, {1: [1,2,3,4]})

Analysis

B = a.copy (): shallow copy, an and b are separate objects, but their child objects still point to the unified object (which is a reference).

B = copy.deepcopy (a): deep copy, an and b completely copy the parent object and its children, and the two are completely independent.

More Instanc

The following examples are copy.copy (shallow copy) and (copy.deepcopy) using the copy module:

Example

#! / usr/bin/python#-*-coding:utf-8-*-import copya = [1, 2, 3, 4, ['await,' b']] # original object b = a # assignment, pass the reference of the object c = copy.copy (a) # object copy, shallow copy d = copy.deepcopy (a) # object copy Deep copy a.append (5) # modify object aa [4] .append ('c') # modify the array object print ('a =', a) print ('b =', b) print ('c =', c) print ('d =', d) in object a

The output of the above example is as follows:

('a =', [1, 2, 3, 4, ['a', 'baked,' c'], 5])

('b =', [1, 2, 3, 4, ['await,' baked,'c'], 5])

('c =', [1, 2, 3, 4, ['await,' baked,'c']])

('d =', [1, 2, 3, 4, ['await,' b']])

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