python动态加载技术解析

class Animal:
    def __init__(self, name, legs) -> None:
        self.name = name
        self.legs = legs
    def get_legs(self):
        return self.legs
    def get_name(self):
        return self.name
animal = Animal('dog', 4)
print(dir(animal))
['__class__', '__delattr__', '__dict__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', '__weakref__', 'get_legs', 'get_name', 'legs', 'name']

class T1:
    def test_test11(self):
        print('test11')
    def test_test22(self):
        print('test22')
class Test(T1):
    def test_test1(self):
        print('test1')
    def test_test2(self):
        print('test2')
test_obj = Test()
for test in [ 'test_test1',  'test_test2', 'test_test11', 'test_test22']:
    method = getattr(test_obj, test) # 如果该函数不存在会raise exception
    method()
# 可以修改如下
test_obj = Test()
for test in [ 'test_test1',  'test_test2', 'test_test11', 'test_test22']:
    method = getattr(test_obj, test, lambda :'donothing') # 如果不存在就运行一个匿名函数，实际就是一个默认值
    method()

#mymodule/mytest.py
def helloworld():
    print('hello world')
class MyModule:
    def print_hello(self):
        print(f'hello from {self.__class__}')
# test.py
import importlib
def import_method1():
    """From module"""
    module = importlib.import_module('mymodule.mytest')
    module.helloworld()
    my_module_obj = module.MyModule()
    my_module_obj.print_hello()
def import_method2():
    """From file path"""
    file = 'mymodule/mytest.py'
    module_name = 'mytest'
    # loading module
    spec = importlib.util.spec_from_file_location(module_name, file)
    module = importlib.util.module_from_spec(spec)
    #execute module
    spec.loader.exec_module(module) 
    # invoke methods
    module.helloworld()
    my_module = module.MyModule()
    my_module.print_hello()

# mytest/myfile.py
import sys
class Test1:
    def setup(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
    def teardown(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
    def run(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
class Test2:
    def setup(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
    def teardown(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
    def run(self):
        print(f" {self.__module__}.{self.__class__.__name__}.{sys._getframe().f_code.co_name}")
# test.py
import importlib
libs = 'mytest.myfile'
class_names = ['Test1', 'Test2']
methods = ['setup', 'run'， 'teardown', 'hello'] # hello不存在的
my_import = importlib.import_module(libs)
for cls_ in class_names:
    Clss = getattr(my_import, cls_) # 获取模块下的类
    my_class = Clss() # 实例化
    for m in methods:
        method = getattr(my_class, m, lambda: "DoNothing") # 获取类方法， 默认lambda为了防止函数不存在
        method() #  执行方法
# output
 mytest.myfile.Test1.setup
 mytest.myfile.Test1.run
 mytest.myfile.Test1.teardown
 mytest.myfile.Test2.setup
 mytest.myfile.Test2.run
 mytest.myfile.Test2.teardown

# 如上代码，我们下面的方式
d1 = __import__(libs)
for cls_ in class_names:
    Clss = getattr(my_import, cls_) # 获取模块下的类
    my_class = Clss() # 实例化
    for m in methods:
        method = getattr(my_class, m, lambda: "DoNothing") # 获取类方法
        method() #  执行方法

import_string = "import mytest.myfile as myfile"
exec(import_string )
t1 = myfile.Test1()
t1.setup()

squre = lambda x: x*x
squre(5)
25

def my_function(a, b, callback_func):
        ....
        if xxx:
                callback_func(**kwargs)

import time
import re
def follow_file_with_timeout(tailed_file,callback_func, timeout=10):
    with open(tailed_file) as file_:
        file_.seek(0,2) # Go to the end of file
        start_time = time.time()
        while time.time() - start_time < timeout:
            curr_position = file_.tell()
            line = file_.readline()
            if not line:
                file_.seek(curr_position)
                time.sleep(1)
            else:
                callback_func(line)
def my_search(line):
    if line:
        matched = re.search('Yourpatternhear', line)
        if matched:
            print(line)
follow_file_with_timeout('test.txt', my_search)