How can I open multiple files within a single `with` statement in Python?

Opening Multiple Files in a Single with Statement

When performing file input and output in Python using the with statement, there are certain techniques you can employ to optimize your code. One such technique involves opening multiple files within the same with block. This proves particularly useful when working with input and output files simultaneously.

Nested with Blocks

In earlier versions of Python, such as 2.5 and 2.6, it was necessary to nest with blocks for multiple file operations. For instance, consider the following example:

<code class="python">def filter(txt, oldfile, newfile):
    with open(newfile, 'w') as outfile:
        with open(oldfile, 'r', encoding='utf-8') as infile:
            for line in infile:
                # ...</code>

In this code, the open function is called twice, creating separate file objects for input and output.

Comma-Separated open() Statements

However, in Python 2.7 and 3.1 onwards, you can simplify this process by comma-separating multiple open() statements within a single with block:

<code class="python">def filter(txt, oldfile, newfile):
    with open(newfile, 'w'), open(oldfile, 'r', encoding='utf-8') as (outfile, infile):
        for line in infile:
            # ...</code>

This concise syntax allows you to work with multiple files simultaneously, significantly improving code readability and reducing indentation levels.

Additional Considerations

Remember that explicitly returning from a Python function is unnecessary as the language automatically exits the function at the end. Additionally, if your code must support Python versions 2.5, 2.6, or 3.0, consider nesting with blocks instead of using the comma-separated approach to ensure compatibility.

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