Does reading an entire file leave the file handle open?
When opening a file using the with
statement, the file is automatically closed after the block:
If you directly open a file without the with
statement, remember to manually close it:
Upon executing the statement in CPython, due to garbage collector’s reference counting, the file will get promptly closed as soon as it becomes unreachable. Even so, it is not advisable to rely on this as it can lead to potential resource leaks.
A closer look at with
Statement
The with
statement, brought to light in PEP 343, serves to ensure cleanup of resources whenever you're done with them.
Old-school file handling
When a file is opened devoid of with
, it will remain open until explicitly closed or the program execution gets over:
The modern days with pathlib
If you're a fan of concise and elegant programming, then pathlib
introduced in Python 3.4 might interest you:
Don't worry if you're using an older version of Python, simply install pathlib2
to get similar functionality.
Secret ingredients of resource management
Serving large files
When the file happens to be huge, a wise way to use less memory is reading the file line by line:
Adding error handling
In case of pathlib.read_text()
, encoding errors can be handled straightaway:
Sprinkle strip() to clean up
Clean data is critical when processing files. .strip()
helps in removing any whitespace or newlines:
Acing resource management and longevity
Beware of the file handlers
Avoid expecting finalizers to close files. Their behavior might not be consistent upon termination of the program leading to unsettled resources.
Mind the leaks
Poor resource and file handle management can lead to resource leaks. In turn, it can affect system performance or even block operations needing those resources.
Optimizing script performance
A well-placed context manager can lead to better script performance by ensuring file handles aren't left open needlessly.
Knowing when to close up
It's vital to grasp when to close file handles:
- After any direct file operation like
.read()
,.readlines()
, etc., if not using 'with'. - When using temporary files that you manipulate programmatically.
- Prior to deleting or altering a file’s properties; else it might cause a permission error.
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