How to Open Multiple Files Simultaneously with the \'with\' Statement?

Opening Multiple Files with the 'with' Statement

When working with file I/O in Python, the 'with open()' statement provides a convenient way to open and close files automatically. However, if you need to open multiple files simultaneously, you might encounter limitations using the traditional approach.

In the following code, we have two files to work with: an input file 'oldfile' to read from, and an output file 'newfile' to write to.

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

As you can see, we have to nest the 'with' statements to open the files sequentially. This can lead to issues if an exception occurs while working with one of the files.

Fortunately, Python offers a more efficient solution: using multiple 'open()' statements within a single 'with' statement. This is achieved by comma-separating the files:

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

This syntax allows you to open both files simultaneously and access them as 'outfile' and 'infile' respectively. Additionally, the files will be closed automatically when the 'with' block exits, ensuring proper resource management.

This approach simplifies the code and eliminates potential issues caused by nested 'with' statements. It is supported in Python versions 2.7 and 3.1 or newer. For older Python versions, you can use contextlib.nested or continue to nest the 'with' statements as before.

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