爬虫技术：数据处理josn和pickle模块

一：json模块

json模块的作用就是讲json字符串（"{"a":1,"b":1}"）和python能够识别的字典进行相互转换。

import json
import pickle
a = """
{'a'::1,
'c':2}
"""

ret = json.loads(a)
print(ret)

# 结果
json.decoder.JSONDecodeError: Expecting property name enclosed in double quotes: line 2 column 2 (char 2)

a不是标准的json字符串，标准的字符串必须使用双引号进行包裹，这点非常重要。


a = """
{"a":1,
"c":2}
"""

ret = json.loads(a)
print(ret)

print(ret["a"])

# 结果
{'a': 1, 'c': 2}
1

结论：loads: josn字符串---->和python字典之间的转换

import json
import pickle
a = {'a':1,'b':2}

ret = json.dumps(a)  # 将pyhton字典转换为josn字符串，这种情况下对于引号的限制没有那么严格
print(ret)

print(type(ret))

{"a": 1, "b": 2}
<class 'str'>

二：picke模块：将字节和python对象之间进行转换

import pickle
a = {'a':1,'b':2}

b = "哈哈"

c = 1

d = [1,2,3]

ret1 = pickle.dumps(a)

print(ret1)

# b'\x80\x03}q\x00(X\x01\x00\x00\x00aq\x01K\x01X\x01\x00\x00\x00bq\x02K\x02u.'

ret2 = pickle.dumps(b)

print(ret2)

# b'\x80\x03X\x06\x00\x00\x00\xe5\x93\x88\xe5\x93\x88q\x00.'

ret3 = pickle.dumps(c)

print(ret3)

# b'\x80\x03K\x01.'

ret4 = pickle.dumps(d)

print(ret4)

# b'\x80\x03]q\x00(K\x01K\x02K\x03e.'

with open("demo.txt","wb") as f:
    f.write(ret1)



这种情况，就要看ret1的编码格式是什么，python中提供了chardet模块来检查编码格式
import chardet
print(chardet.detect(ret1))
# 结果
{'encoding': 'Windows-1252', 'confidence': 0.73, 'language': ''}

import pickle
import chardet
a = {'a':1,'b':2}

d = [1,2,3]

f = open("test.txt","wb")

pickle.dump(d,f)  # 不同于dumps返回一个二进制的结果，dump直接将文件写入指定位置

f.close()

import pickle
import chardet
a = {'a':1,'b':2}

d = [1,2,3]

ret = pickle.dumps(d)

print(ret)

# b'\x80\x03]q\x00(K\x01K\x02K\x03e.'

ret1 = pickle.loads(ret)   # pickle必须接收的是picke自己dumps的二进制类型文件

print(ret1)

# [1, 2, 3]

import pickle
import chardet
a = "1"

ret = a.encode("utf-8")
print(ret)

ret1 = pickle.loads(ret)  # loads的数据，必须是dumps自己处理过的类型才行
print(ret1)

# 结果
_pickle.UnpicklingError: could not find MARK

import pickle
import chardet
a = "1"

ret = a.encode("Windows-1252")
print(ret)

ret1 = pickle.loads(ret)
print(ret1)

# 结果
_pickle.UnpicklingError: could not find MARK

 laod方法

import pickle
import chardet

with open("demo.txt","rb") as f:
    ret = pickle.load(f)
print(ret)

# 结果
{'a': 1, 'b': 2}