如何使用 open with 语句打开文件

我正在研究如何在 Python 中进行文件输入和输出。我编写了以下代码，将一个文件中的名称列表（每行一个）读取到另一个文件中，同时根据文件中的名称检查名称并将文本附加到文件中出现的位置。该代码有效。可以做得更好吗？

我想用with open(...输入和输出文件的语句，但看不到它们如何位于同一块中，这意味着我需要将名称存储在临时位置。

def filter(txt, oldfile, newfile):
    '''\
    Read a list of names from a file line by line into an output file.
    If a line begins with a particular name, insert a string of text
    after the name before appending the line to the output file.
    '''

    outfile = open(newfile, 'w')
    with open(oldfile, 'r', encoding='utf-8') as infile:
        for line in infile:
            if line.startswith(txt):
                line = line[0:len(txt)] + ' - Truly a great person!\n'
            outfile.write(line)

    outfile.close()
    return # Do I gain anything by including this?

# input the name you want to check against
text = input('Please enter the name of a great person: ')    
letsgo = filter(text,'Spanish', 'Spanish2')

Python允许放置多个open()单个语句中with。你用逗号分隔它们。那么你的代码将是：

def filter(txt, oldfile, newfile):
    '''\
    Read a list of names from a file line by line into an output file.
    If a line begins with a particular name, insert a string of text
    after the name before appending the line to the output file.
    '''

    with open(newfile, 'w') as outfile, open(oldfile, 'r', encoding='utf-8') as infile:
        for line in infile:
            if line.startswith(txt):
                line = line[0:len(txt)] + ' - Truly a great person!\n'
            outfile.write(line)

# input the name you want to check against
text = input('Please enter the name of a great person: ')    
letsgo = filter(text,'Spanish', 'Spanish2')

不，你不会通过明确地添加任何内容来获得任何东西return在你的函数结束时。您可以使用return提前退出，但你在最后才得到它，并且函数将在没有它的情况下退出。 （当然，对于返回值的函数，您可以使用return指定要返回的值。）

使用多个open()项目与withPython 2.5 中不支持with语句是在 Python 2.6 中引入的，但在 Python 2.7 和 Python 3.1 或更高版本中受支持。

http://docs.python.org/reference/compound_stmts.html#the-with-statement http://docs.python.org/reference/compound_stmts.html#the-with-statement http://docs.python.org/release/3.1/reference/compound_stmts.html#the-with-statement http://docs.python.org/release/3.1/reference/compound_stmts.html#the-with-statement

如果您正在编写必须在 Python 2.5、2.6 或 3.0 中运行的代码，请嵌套with其他答案建议或使用的陈述contextlib.nested http://docs.python.org/library/contextlib.html#contextlib.nested.