Files serve as persistent storage beyond the runtime memory of a program. Python provides a built-in streaming interface for creating, reading, updating, and removing files on disk.

Stream Initialization

Invoke open() to obtain a file handle:

handle = open("report.txt", mode="r", encoding="utf-8")

The mode argument controls access behavier:

• r — read from the beginning (default)
• w — truncate and open for writing
• a — preserve existing bytes and append
• x — exclusive creation; raises FileExistsError if the path is taken
• b — binary access (e.g., rb, wb)
• t — text decoding with the specified encoding (default)

After finishing, explicitly release system resources:

handle.close()

Sequential Reading

Slurp the entire contents into a string:

f = open("dataset.csv", "rt", encoding="utf-8")
payload = f.read()
print(payload)
f.close()

Process one record at a time to keep memory usage low:

f = open("dataset.csv", "rt", encoding="utf-8")
for record in f:
    print(record.strip())
f.close()

Persisting Data

Overwrite mode (w) creates the file if absent, otherwise empties it:

f = open("notes.txt", "wt", encoding="utf-8")
f.write("Meeting scheduled for 10 AM\n")
f.write("Prepare slide deck\n")
f.close()

Append mode (a) inserts bytes at the current end-of-file:

f = open("notes.txt", "at", encoding="utf-8")
f.write("Follow-up required\n")
f.close()

Automatic Resource Management

A context manager guarantees closure regardless of control flow:

with open("dataset.csv", "r", encoding="utf-8") as f:
    payload = f.read()
    print(payload)

The same pattern applies to output:

with open("notes.txt", "w", encoding="utf-8") as f:
    f.write("Line one\n")
    f.write("Line two\n")

Metadata and Cleanup

Validate existence before destructive actions:

from pathlib import Path

source = Path("notes.txt")
if source.is_file():
    print("Located on disk")
else:
    print("Not found")

Remove a file permanently:

from pathlib import Path

target = Path("temp.txt")
if target.exists():
    target.unlink()
    print("Deleted")