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#2
时光流逝2020-02-23 17:47
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我写了下面一段代码：
一、建立了一个students列表，列表元素的学生信息为包含2个键的字典。
二、建立了一个teached_students列表，他是对students列表的一个截取。
三、修改学生列表中一个元素，删除一个元素。（选取的这两个元素都包含在teached_students列表中）
四、发现问题：修改student列表中元素value时，为什么teached_students列表中的元素value也变了？
难道这是说对于字典列表元素的复制，并没有真正的分配内存空间，而是仅仅做了一个索引？
但若是如此，为什么删除students列表中的元素时，teached_students列表中的元素没有同时被删除呢？
students = []
stu_id = 1
score = 100
for num in range(1,12):
new_student = {
'stu_id':stu_id,
'score':score
}
students.append(new_student)
stu_id = stu_id + num
score = 100 - num* 2
print("--------print students information-------")
for std in students:
print(std.items())
'''define teached_students list and initial it'''
teached_students = []
teached_students = students[-5:]
print("\n--------print teached_students information-------")
for std in teached_students:
print(std.items())
'''modify students[-3] and delelet students[-1]'''
students[-3]['score'] = 59
del students[-1]
print("\n----------modify students[-3] and delelet students[-1]-------")
print("-----------why does the \"teached_students[-3]\" changed but \"teached_students[-1]\" haven't been removed?---------")
for std in teached_students:
print(std.items())
print("\n--------print students information-------")
for std in students:
print(std.items())
运行结果如下：
--------print students information-------
dict_items([('stu_id', 1), ('score', 100)])
dict_items([('stu_id', 2), ('score', 98)])
dict_items([('stu_id', 4), ('score', 96)])
dict_items([('stu_id', 7), ('score', 94)])
dict_items([('stu_id', 11), ('score', 92)])
dict_items([('stu_id', 16), ('score', 90)])
dict_items([('stu_id', 22), ('score', 88)])
dict_items([('stu_id', 29), ('score', 86)])
dict_items([('stu_id', 37), ('score', 84)]) //修改此元素的score值
dict_items([('stu_id', 46), ('score', 82)])
dict_items([('stu_id', 56), ('score', 80)]) //删除此元素
--------print teached_students information-------
dict_items([('stu_id', 22), ('score', 88)])
dict_items([('stu_id', 29), ('score', 86)])
dict_items([('stu_id', 37), ('score', 84)])
dict_items([('stu_id', 46), ('score', 82)])
dict_items([('stu_id', 56), ('score', 80)])
----------modify students[-3] and delelet students[-1]-------
-----------why does the teached_students list changed?---------
dict_items([('stu_id', 22), ('score', 88)])
dict_items([('stu_id', 29), ('score', 86)])
dict_items([('stu_id', 37), ('score', 59)]) //为什么此元素的score值变了？
dict_items([('stu_id', 46), ('score', 82)])
dict_items([('stu_id', 56), ('score', 80)]) //为什么此元素没被删除？！！！
--------print students information-------
dict_items([('stu_id', 1), ('score', 100)])
dict_items([('stu_id', 2), ('score', 98)])
dict_items([('stu_id', 4), ('score', 96)])
dict_items([('stu_id', 7), ('score', 94)])
dict_items([('stu_id', 11), ('score', 92)])
dict_items([('stu_id', 16), ('score', 90)])
dict_items([('stu_id', 22), ('score', 88)])
dict_items([('stu_id', 29), ('score', 86)])
dict_items([('stu_id', 37), ('score', 59)])
dict_items([('stu_id', 46), ('score', 82)])