Why Does My Python File Iteration Fail on Subsequent Attempts?

File Iteration Issue with Subsequent Attempts

Iterating over a file using for loop is widely used in Python to process data line by line. However, an intriguing issue arises when trying to iterate on the same file multiple times.

When attempting to iterate on an open file a second time, the readlines() method yields no output, despite successfully reading the entire file on the initial iteration. To resolve this issue, it becomes necessary to either close the file and reopen it or use f.seek(0) to reset the file pointer.

Understanding this behavior involves recognizing that the initial readlines() operation reads the entire file into memory. This means that when trying to iterate a second time, there's no more data to be read as the file pointer has reached the end.

To avoid such limitations, consider employing the with syntax, which automatically handles file closing. The following modification ensures proper iteration:

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

This approach ensures that the file is automatically closed when the block completes, allowing for multiple successful iterations without the need for manual closing and reopening.

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