Getting Started with Python     

DAY 19

Today's content: shelve module, xml module, configparser module, hashlib module

1.shelve (a dictionary object module automatic serialization)

    What is the shelve module
        is also a serialization
    method
        . 1. opne
        2. Read and write
        3. close
    Features: The use method is relatively simple. Provide a file name to start reading
         and writing. The reading and writing method is the same as that of the dictionary.
         You can use it as a tape. The principle of dictionary with automatic serialization function
    : pickle is used internally, so there is also a problem of poor cross-platform performance. Only you know how to get it.

    Use: Can be considered when writing stand-alone programs

import shelve
# 序列化
sl = shelve.open("shelvetest.txt")
sl["date"] = "8-13"
sl["list1"] = ["123","456"]
sl.close()

# 反序列化
s2 = shelve.open("shelvetest.txt")
print(s2.get("list1"))
s2.close()

2. XML (Extensible Markup Language)
    is a file format
    for writing configuration files or data exchange.
Why do you need XML?
In order         to continue data exchange between different platforms, in
        order to make the exchanged data understandable to the other party, it is necessary to follow a certain syntax standard to write

XML syntax format:
        Any start tag must have an end tag.

        Another simplified syntax is available, where both start and end tags can be represented in one tag. This syntax is followed by a slash (/) immediately before the greater than sign

        The tags must be nested in the proper order.

        All attributes must have a value, and must be enclosed in double quotes around the value.
 Note: There is only one tag in the outermost layer. This tag is called the root tag.
              The first line should have a document declaration for high-speed computers
              . For example: <?xml version="1.0" encoding="utf-8"?>
              When When tags are nested, there will be a hierarchical relationship. If a tag is not wrapped by any other tags, it is the root tag (outermost)

 Usage scenarios:
            1. Configuration file
            2. Regular data exchange such as getting a piece of news from the server

 The difference with json: the
            function is the same, it is a data format
            xml was born before
            json, the data of json is smaller than xml,
            and json is currently the mainstream

 XML processing in python:
            the used module
            ElmentTree represents the element tree of the entire file

            Elment represents a node
                attribute
                1.text The text between the start tag and the end tag
                2.attrib all attributes Dictionary type
                3.tag tag name
                method
                    get Get the value of an attribute
            1. Parse XML to
                find the tag
                find and get it in the subtag The name matches the first
                findall Get all tags whose names match in
                subtags iter(tagname) Find in the full text [all tags that match return an iterator
            2. Generate XML Parse a file
                with ElmentTree
                parse()
                getroot() Get the root The label
                write() is written to the file
            3. Modify an attribute of the xml
                set
                remove a label
                append a label

3.configparser (configuration file parsing module) is
    used to parse read and write configuration files
    Content: section option

What is a configuration file ? A file
            used to provide some information needed by the program to run. Suffix ini cfg
Purpose: easy for users to modify

The content format of the configuration file
        includes only two elements:
        section section
        option options
        A file can have multiple sections
        A section can have multiple options

Core function
    1.sections get all
    sections2.options get all
    options3.get get a value pass in section option

    Note: case insensitive
 

4. What is hashlib
        hash?
            It is an algorithm
            for compressing and mapping data of any length to a fixed-length character (extracting features)
           

        Features of hash:
            1. If the input data is different, the obtained hash value may be the same
            2. The input value cannot be obtained through the hash value
            3. If the algorithm is the same, regardless of the length of the input data, the obtained hash value has the same length

            Because of the above characteristics, the hash algorithm is often used for encryption and file verification.

            There are many
            commonly used encryption methods. MD5 is a hash algorithm . A
            commonly used method to improve security is to add salt
            , which is to make some changes to the data before encryption, such as reversing the order.

List:

import hashlib
md = hashlib.md5()
md.update("hello".encode("utf-8"))
print(md.hexdigest())


# 破解MD5可以尝试撞库   原理: 有一个数据库 里面存放了常见的明文和密文的对应关系 ,
# 所以我可以拿着一个密文取数据库中查找 有没有已经存在的明文  如果有撞库成功  能不能破解凭运气
# 假设我已经拿到了一个众多账号中的一个密码  我可以那这个密码 挨个测试你的所有账号  可能不能碰到运气
pwd_dic = {"123456":"e10adc3949ba59abbe56e057f20f883e","hello":"5d41402abc4b2a76b9719d911017c592"}
for i in pwd_dic:
    if pwd_dic[i] == "5d41402abc4b2a76b9719d911017c592":
        print(i)

The above is the content of this study