Question

基于with statement

加载上下文管理器__exit__()以供以后使用。
调用上下文管理器的__enter__()方法。

我见过其中一个用于zipfile

的用法

问题＆GT; 我已经检查了zipfile的源代码：

/usr/lib/python2.6/zipfile.py

我不知道__enter__和__exit__函数的定义在哪里？

谢谢

Answer 1

zipfile.ZipFile不是2.6中的上下文管理器，已在2.7中添加。

Answer 2

我已将此添加为另一个答案，因为它通常不是初始问题的答案。但是，它可以帮助解决您的问题。

class MyZipFile(zipfile.ZipFile): # Create class based on zipfile.ZipFile
  def __init__(file, mode='r'): # Initial part of our module
    zipfile.ZipFile.__init__(file, mode) # Create ZipFile object

  def __enter__(self): # On entering...
    return(self) # Return object created in __init__ part
  def __exit__(self, exc_type, exc_val, exc_tb): # On exiting...
    self.close() # Use close method of zipfile.ZipFile

用法：

with MyZipFile('new.zip', 'w') as tempzip: # Use content manager of MyZipFile
  tempzip.write('sbdtools.py') # Write file to our archive

如果您输入

help(MyZipFile)

你可以看到原始zipfile.ZipFile的所有方法和你自己的方法： init ，输入和退出。如果需要，您可以添加另一个自己的功能。祝你好运！

Answer 3

使用对象类创建类的示例：

class ZipExtractor(object): # Create class that can only extract zip files
  def __init__(self, path): # Initial part
    import zipfile # Import old zipfile
    self.Path = path # To make path available to all class
    try: open(self.Path, 'rb') # To check whether file exists
    except IOError: print('File doesn\'t exist') # Catch error and print it
    else: # If file can be opened
      with open(self.Path, 'rb') as temp:
        self.Header = temp.read(4) # Read first 4 bytes
        if self.Header != '\x50\x4B\x03\x04':
          print('Your file is not a zip archive!')
        else: self.ZipObject = zipfile.ZipFile(self.Path, 'r')

  def __enter__(self): # On entering...
    return(self) # Return object created in __init__ part
  def __exit__(self, exc_type, exc_val, exc_tb): # On exiting...
    self.close() # Use close method of our class

  def SuperExtract(member=None, path=None):
    '''Used to extract files from zip archive. If arg 'member'
    was not set, extract all files. If path was set, extract file(s)
    to selected folder.'''
    print('Extracting ZIP archive %s' % self.Path) # Print path of zip
    print('Archive has header %s' % self.Header) # Print header of zip
    if filename=None:
      self.ZipObject.extractall(path) # Extract all if member was not set
    else:
      self.ZipObject.extract(mamber, path) # Else extract selected file

  def close(self): # To close our file
    self.ZipObject.close()

用法：

with ZipExtractor('/path/to/zip') as zfile:
  zfile.SuperExtract('file') # Extract file to current dir
  zfile.SuperExtract(None, path='/your/folder') # Extract all to selected dir

# another way
zfile = ZipExtractor('/path/to/zip')
zfile.SuperExtract('file')
zfile.close() # Don't forget that line to clear memory

如果你运行'help（ZipExtractor）'，你会看到五种方法：

__init__, __enter__, __exit__, close, SuperExtract

我希望我帮助过你。我没有测试它，所以你可能需要改进它。

Answer 4

cat-plus-plus是对的。但如果你愿意，你可以编写自己的类来添加“遗漏”功能。您需要做的就是在您的类中添加两个函数（基于zipfile）：

def __enter__(self):
  return(self)
def __exit__(self, exc_type, exc_val, exc_tb):
  self.close()

那应该够了，AFAIR。

为zipfile定义的enter和exit在哪里？

4 个答案:

为zipfile定义的__enter__和__exit__在哪里？

4 个答案:

为zipfile定义的enter和exit在哪里？