Python interview one hundred questions - lists, tuples and dictionaries (2)

table of Contents

11. Del difference and pop on the delete list elements
12. Sort the list with a lambda expression
13. What type of data dictionary key support
14. Using a microtome type of object generator
15. The cycle produces a list generator becomes
16. How Python dictionaries with JSON string Huzhuan

Difference 11.del and pop on the delete list elements

13. sort the list with a lambda expression

a =[
    {'name': 'Bill', 'age': 40},
    {'name': 'Mike', 'age': 10},
    {'name': 'John', 'age': 20}
]

print(sorted(a, key=lambda x:x['age']))
[{'name': 'Mike', 'age': 10}, {'name': 'John', 'age': 20}, {'name': 'Bill', 'age': 40}]

a.sort(key=lambda x:x['age'], reverse= True)
print(a)
[{'name': 'Bill', 'age': 40}, {'name': 'John', 'age': 20}, {'name': 'Mike', 'age': 10}]

to sum up

13. What type of data dictionary key support

Lists and dictionaries can not be used as key

Because the key is not changed, but the values ​​are lists and dictionaries can change, once the changes could not find the corresponding value

14. Use of a slice type of object generator

from itertools import islice

gen = iter(range(10))
print(type(gen))

for i in islice(gen, 2, 6):
    print(i, end=' ')

to sum up

15. The list generator into the generated cycle

a = [i for i in range(10)]
print(a)	# [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
print(type(a))	# <class 'list'>

b = (i for i in range(10))
print(type(b))	# <class 'generator'>

for i in b:
    print(i, end=' ')
# 0 1 2 3 4 5 6 7 8 9 
x = (1, 2, 3, 4)
print(type(x))	# <class 'tuple'>

Summary

not for, it will become a tuple

16.Python dictionary and how JSON string Huzhuan

import json

a = {'a': 1, 'b': '2', 'c': 'x'}
print(a)	# {'a': 1, 'b': '2', 'c': 'x'}
print(type(a))	# <class 'dict'>

json_str = json.dumps(a)
print(json_str)	# {"a": 1, "b": "2", "c": "x"}
print(type(json_str))	# <class 'str'>

a1 = json.loads(json_str)
print(a1)	# {'a': 1, 'b': '2', 'c': 'x'}
print(type(a1))	# <class 'dict'>

to sum up