Python built-in module (3)

 

hashlib module

Convert any length of data into a fixed-length data string (usually represented by a hexadecimal string) through a function.

Using hashlib in Python2:

import hashlib
m = hashlib.md5()
# m <md5 HASH object @ 0x0000000001E5C800>
src = "ling"
m.update(src)
print(m.hexdigest())
# 24c10be286b009f797d53126790fcfd8

Using hashlib in Python3:

import hashlib
m = hashlib.md5()
 # m = hashlib.md5("123".encode("utf-8")) # Add a random number 
# m <md5 HASH object @ 0x0000000001E5C800> 
src = bytes( " ling " ,encoding = " utf-8 " )
src1 = bytes("zhangsan",encoding="utf-8")
m.update(src)
m.update(src1)
print(m.hexdigest())

If the amount of data is large, update() can be called multiple times in blocks.

 

StringIO module

Sometimes data reading and writing is not necessarily a file, but can also be read and written in memory. StringIO is to read and write str in memory.

from io import StringIO
 # StringIO can only store strings 

stringIO = StringIO ()
stringIO.write("hello,world\n")
stringIO.write( " hello,python " )
 print (stringIO.getvalue())
 # hello,world 
# hello,python 
stringIO.truncate(0) #Empty   all written content 
stringIO.flush() #Flush       the internal buffer 
print ( stringIO.getvalue ()) #No
 output, the content has been emptied

StringIO can also be read like a file:

from io import StringIO
stringIO = StringIO("hello\nworld")
while True:
    s = stringIO.readline()
    if s == "":
        break
    print(s.strip())

 

BytesIO模块

StringIO can only operate on str. If you want to operate binary data, you need to use BytesIO.

from io import BytesIO
bytesIO = BytesIO()
bytesIO.write("中文".encode("utf-8"))
print(bytesIO.getvalue())  # 读取内容

Note: What is written is not str, but utf-8 encoded bytes.

BytesIO can also read the contents in the same way as reading a file:

from io import BytesIO
bytesIO = BytesIO(b'\xe4\xb8\xad\xe6\x96\x87')
bytesIO.read()
b ' \ xe4 \ xb8 \ limit \ xe6 \ x96 \ x87 '

 

Json module

json refers to JavaScript Object Notation, and json is a lightweight text data interchange format.

usage:

loads convert strings to python objects (such as dictionaries, lists, etc.)

dumps converts python objects to strings

load converts the file into a python object

dump writes python objects to a file

 

To operate on strings, convert strings into python objects:

import json
test = '''[{"a":1, "aa":11, "aaa":111},{"b":2, "bb":22, "bbb":333}]'''
print(type(test))           # <type 'str'>
newTest = json.loads(test)  # 把字符串转换成python对象
print(type(newTest))        # <type 'list'>
print(newTest[0]["a"])      # 1

For python2 garbled problem, use json to solve:

import json
a = dict(hello= " Hello " )
 print (a)             # {' hello ': '\xe4\xbd\xa0\xe5\xa5\xbd'} 
print (a[ " hello " ])    #Hello print ( json.dumps(a,ensure_ascii=False)) #Convert   
python objects to strings # {"hello": "Hello"}

To operate on files, files and python objects are converted to each other:

import json
test = {"a":1, "b":2}
with codecs.open("1.txt","w") as f:
    json.dump(test, f) #Write     python object to file 
with codecs.open( " 1.txt " , " r " ) as f:
    aa = json.load(f) #Convert      the file into a python object, aa is unicode type 
    print (aa)         # {u'a': 1, u'b': 2} 
    print (type(aa))   # <type 'dict'>