Module expansion and cognition

  · Process oriented programming

  · Module introduction

  · import sentence pattern

  · from...import... Sentence pattern

  · Circular import problem

  · Absolute import and relative Import

  · Software development catalog specification

  1, Process oriented programming

    Process oriented programming is like designing a product pipeline, and the results are visible.

    The drawback of process oriented is that once the function is to be modified, it needs to be transformed as a whole (pulling one hair and moving the whole body)

def get_info():
    username = input('username>>>:').strip()
    password = input('password>>>:').strip()
    if len(username) == 0 or len(password) == 0:
        print('User name or password cannot be empty')
        return
    user_idf = {
        '1':'admin',
        '2':'user',
    }
    print(user_idf)
    choice = input('Please select your identity>>>:').strip()
    if choice in user_idf:
        id = user_idf.get(choice)
        return deal_data(username, password,id)
    else:
        print('Illegal input')
        return

def deal_data(username,password,id):
    data = '%s|%s|%s\n'%(username,password,id)
    return save_data(data)

def save_data(data):
    with open(r'userinfo','a',encoding='utf8') as f:
        f.write(data)
    print('login was successful')


get_info()

  Two. Module introduction

    1. What is a module?

        Module: a combination of a series of functions

    2. Why use modules?

        In order to improve development efficiency

    3. Three sources of modules

        1. Built in

        2. Of third parties

        3. Customized

    4. Four forms of modules

        1. Code written in python

        2. C or C + + extensions that have been compiled as shared libraries or DLL s

        3. Pack a group of modules

        4. Use C to write and link to the built-in module of python interpreter

  3, import sentence pattern

    When learning the module   Be sure to distinguish who is the import file and who is the module file

    Import file module   The file suffix must not be added

    Import the same module multiple times   It will only be executed once

    What happened when the module was imported for the first time

        1. Run the imported file to generate the global namespace of the store waiter of the file

        2. Operation documents

        3. Generate file global namespace   Run the code in the file   Archive all the generated names and namespaces

        4. When importing, the file namespace generates a file name that points to the file global namespace

  import sentence after importing the module

        You can use all the names in the module by clicking the module name   And there will certainly be no conflict

  4, from...inport

     from...inport... Multiple imports will only import once

        1. First generate the global namespace of the execution file

        2. Execute module file   Generate the global namespace of the module

        3. Archive all the names generated after execution in the module in the module namespace

        4. In the execution file, there is a value pointed to by money in the namespace of the money execution module

     from...inport... Import a name by name

        Just write your name when you use it   But when the current namespace has the same name

          There will be conflict   The used name becomes the current namespace

# money = 999
# print(money)
money = 999
# def read1():
#     print('Miss Dong')
# read1()
change()
print(money)

  5, Import module extension usage

    1. Alias

        You can alias either the module name or a name in the module

    2. Continuous import

        import   Module name 1, module name 2

            Multiple modules can be imported continuously   However, only when multiple modules have similar functions or belong to the same series

            If the functions are different and do not belong to a series   It is recommended to import by branch

        import Module name 1
        import Module name 2
    from Module name 1 import Name 1,Name 2,Name 3

    3. General import

from md import *  # Import all the names in the module(*Represents all)
    print(money)
    print(read1)
    print(read2)
    print(change)
    __all__ = ['money','read1']  # It can be used in the imported module file__all__Specifies the name that can be imported

  6, Determine file type

    Determine whether the py file is a module file or an execution file

    _ name_ Returns when the file is an executable file_ main_

    If the file is imported as a module, the file name is returned

if __name__ == '__main__':
  read1()
"""stay pycharm You can knock directly in main Press tab Key to complete automatically if judge"""

  7, Circular import

    In the future, when we import modules, if circular import occurs     It means that your program design is unreasonable

    Remember that circular import is not allowed in the future programming career

    Make mistakes again and again:

        1. Change position

Put the sentences imported from each other at the end of the code

        2. Function form

Put the imported sentence into the function body code   Wait until all names are loaded before calling

  8, Order of module import

    1. Search from memory first

    2. Search in the built-in module

    3. Finally, go to sys.path to find the system path

    If none, an error is reported

# I'll give it later py Try not to conflict with the built-in module name when naming the file

import sys
print(sys.path)  # The first element in the result is always the path of the current execution file


Solution when a custom module cannot be found
    1.Manually add the path of the module to the sys.path in
        import sys
        sys.path.append(r'D:\py20\day18\aaa')
    2.from...import...Sentence pattern
        from Folder name.Folder name import Module name
        from Folder name.Module name import name

     -------- That's all for today. I'll see you next time----------