How Can You Open Multiple Files Simultaneously Using Python\'s \'with open\' Statement?

Opening Multiple Files with the "with open" Statement in Python

Python's "with open" statement is a convenient way to open and work with files within a context manager. However, by default, it only allows opening one file at a time. But what if you want to modify or read from multiple files simultaneously?

Merging "with open" Calls

Short Answer: Since Python 2.7 or 3.1, you can simply list multiple "with open" statements without the "and" keyword:

with open('a', 'w') as a, open('b', 'w') as b:
    # Perform actions on file handles 'a' and 'b'

Nesting "with open" Statements

In earlier Python versions, you could use the "contextlib.nested()" method to nest context managers. However, this approach is not recommended for opening multiple files.

Contextlib.ExitStack

For situations where you need to open a variable number of files at once, Python 3.3 introduced the "contextlib.ExitStack" context manager. This allows you to add multiple file objects to a stack and exit in the proper order:

import contextlib
with contextlib.ExitStack() as stack:
    files = [stack.enter_context(open(fname)) for fname in filenames]
    # Work with 'files' here

Sequential File Processing

Keep in mind that, in most cases, it's more efficient and idiomatic to process files sequentially. For example, you can use a loop to open and work with each file individually:

for fname in filenames:
    with open(fname) as f:
        # Process file 'f' here

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