Detailed introduction to the method of dynamically loading packages in Python

The example in this article summarizes the method of dynamically loading packages in Python. Share it with everyone for your reference, the details are as follows:

There are three ways to dynamically load modules

1. Use the system function __import_()

stringmodule = __import__('string')

2. Use imp module

import imp 
stringmodule = imp.load_module('string',*imp.find_module('string'))
imp.load_source("TYACMgrHandler_"+app.upper(), filepath)

3. Use exec

import_string = "import string as stringmodule"
exec import_string

Whether the variable exists

1. hasattr(Test,'t')
2. 'var' in locals ().keys()
3. 'var' in dir()
4. vars().has_key('s')

Dynamicly add attributes

class Obj(object):
  pass
def main():
  list=["a","b", "c"]
  for i inrange(1,len(list),2):
    Obj = type('Obj',(),{list[i]:lambdaself,s:obj.__setattr__(s.split(" = ")[0],s.split(" = ")[1])})
  obj =Obj()
  for i inrange(0,len(list),2):
    obj.__setattr__(list[i],list[i])  
  obj.a =1
  obj.b("a =2")
  obj.b("c =3")
  printobj.a
  printobj.c
if __name__ == '__main__':
  main()

Dynamic loading package:

def test(s,e):
  print s
  print e
class C():
  def __init__(self,name):
    print name
  def test(self):
    print 'class!!!'

Loader code:

class Dynload():
  def __init__(self,package,imp_list):
    self.package=package
    self.imp=imp_list
  def getobject(self):
    return __import__(self.package,globals(),locals(),self.imp,-1)
  def getClassInstance(self,classstr,*args):
    return getattr(self.getobject(),classstr)(*args)  
  def execfunc(self,method,*args):
    return getattr(self.getobject(),method)(*args)
  def execMethod(self,instance,method,*args):
    return getattr(instance,method)(*args)
#Test:
dyn=Dynload('util.common',['*'])
ins=dyn.getClassInstance('C','gao')
dyn.execMethod(ins,'test')
dyn.execfunc('test','Hello','function!')

Load the specified file according to the name

def loadapp(self, app):
    filepath="mgr/"+app+".py"
    if os.path.exists(filepath):
      imp.load_source("TYACMgrHandler_"+app.upper(), filepath)
//修改了app.py，从新调用这个函数，新的代码自动生效

Calling the corresponding method according to the name

return getattr(self, op)(args.get("port"), args) //op="start" args=dict
getattr(self, self.request.method.lower())(*args, **kwargs)

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