Python奇淫技巧第二弹之装13语法(未完待续)

1. 动态导入代码

• 动态导入模块：使用importlib.import_module，参考Django的动态引入模块

  def import_string(dotted_path):
      """
      Import a dotted module path and return the attribute/class designated by the
      last name in the path. Raise ImportError if the import failed.
      """
      try:
          module_path, class_name = dotted_path.rsplit('.', 1)
      except ValueError as err:
          raise ImportError("%s doesn't look like a module path" % dotted_path) from err
  ​
      module = import_module(module_path)
  ​
      try:
          return getattr(module, class_name) #判断module模块中是否存在class_name属性或者类
      except AttributeError as err:
          raise ImportError('Module "%s" does not define a "%s" attribute/class' % (
              module_path, class_name)
          ) from err
  ​

   

2. 强制关键参数

• 用法：当我们希望函数的某些参数强制使用关键字参数时，可以将强制关键字参数放到某个*后面就能得到这种效果

  >>> def f(a, b, *, c='x', d='y', e='z'):
  ...     return 'Hello'
  ​
  # To pass the value for c, d, and e you 
  # will need to explicitly pass it as 
  # "key=value" named arguments:
  >>> f(1, 2, 'p', 'q', 'v')
  TypeError: 
  "f() takes 2 positional arguments but 5 were given"
  ​
  >>> f(1, 2, c='p', d='q',e='v')
  'Hello'

   

3. 注册退出函数

• atexit.register()装饰器：会在Python解释器中注册一个退出函数，也就是说，他会在脚本退出之前请求调用这个特殊函数

4. print函数的end和sep参数

• print函数的定义

  def print(self, *args, sep=' ', end='\n', file=None): # known special case of print
      """
      print(value, ..., sep=' ', end='\n', file=sys.stdout, flush=False)
      
      Prints the values to a stream, or to sys.stdout by default.
      Optional keyword arguments:
      file:  a file-like object (stream); defaults to the current sys.stdout.
      sep:   string inserted between values, default a space.
      end:   string appended after the last value, default a newline.
      flush: whether to forcibly flush the stream.
      """
      pass

   

• 参数含义：

1. sep：分割值与值，默认是一个空格
2. end：附件到最后一个值，默认是一个新行
3. file：指定打印的输出位置，默认是sys.stdout