open read and close a file in 1 line of code

 

Now I use: 

pageHeadSectionFile = open('pagehead.section.htm','r')
output = pageHeadSectionFile.read()
pageHeadSectionFile.close()

But to make the code look better, I can do: 

output = open('pagehead.section.htm','r').read()

When using the above syntax, how do I close the file to free up system resources?

You don't really have to close it - Python will do it automatically either during garbage collection or at program exit. But as @delnan noted, it's better practice to explicitly close it for various reasons.

So, what you can do to keep it short, simple and explicit: 

with open('pagehead.section.htm','r') as f:
    output = f.read()

Now it's just two lines and pretty readable, I think.

Using CPython, your file will be closed immediately after the line is executed, because the file object is immediately garbage collected. There are two drawbacks, though:

  • In Python implementations different from CPython, the file often isn't immediately closed, but rather at a later time, beyond your control.

  • In Python 3.2 or above, this will throw a ResourceWarning , if enabled.

    • Better to invest one additional line: 

    with open('pagehead.section.htm','r') as f:
    output = f.read()

    This will ensure that the file is correctly closed under all circumstances.

    What you can do is to use the with statement: 

    >>> with open('pagehead.section.htm', 'r') as fin:
...     output = fin.read()

    The with statement will take care to call __exit__ function of the given object even if something bad happened in your code; it's close to the try... finally syntax. For object returned by open , __exit__ corresponds to file closure.

    This statement has been introduced with Python 2.6.

    链接地址: http://www.djcxy.com/p/19628.html

    上一篇: 为每次击中返回周围线路

    下一篇: 用1行代码打开读取和关闭文件