Why Does Iterating Over a Python File Multiple Times Fail, and How Can I Fix It?

Iterating through a File Multiple Times

In Python, iterating over a file using readlines() reads the entire file into memory and stores it as a list of lines. When you iterate over the file again, Python has already reached the end of the file, so there's nothing left to read.

Normal Behavior

Yes, it's normal behavior for iterating over a file multiple times to fail unless you reset the iteration. This is because Python's file IO operates sequentially, moving from the beginning of the file to the end during the first iteration.

Resetting the Iteration

To reset the iteration and read the file again, you have two options:

1. Use f.seek(0): This method allows you to reset the file cursor to the beginning of the file.
2. Close and Reopen the File: Closing the file (f.close()) and then reopening it with the 'r' mode (for reading) will start the iteration from the beginning again.

Using the with Statement

A more convenient approach is to use the with statement, which automatically closes the file when exiting the code block. This allows you to repeatedly iterate over the file without explicitly closing and reopening it:

with open('baby1990.html', 'rU') as f:
    for line in f:
        print(line)

By using the with statement, you can execute the code block multiple times and read the file each time without worrying about resetting the iteration.

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