Master Python File I/O: Open, Read, Write, and Manage Files Efficiently

1. What is a file?

A file stores data so that a program can reuse it later without recreating the content.

2. How to open a file?

Python provides the built‑in open() function for reading and writing files. The typical workflow is three steps: open, operate, close.

open syntax

The open() function returns a file object (file handle).

Basic syntax: f = open(filename, mode) filename : string containing the file name or path.

mode : file access mode, default is read‑only r.

Example:

# Open a file
f = open("1.txt", "w")
f.write("Python is a great language.
Python!!
")
# Close the file
f.close()

Result: the text is written into 1.txt.

3. Access modes

r : read‑only, pointer at start (default).

w : write‑only, overwrite if exists or create new.

a : append, pointer at end, create if not exist.

rb : binary read‑only, pointer at start.

wb : binary write‑only, overwrite or create.

ab : binary append.

r+ : read/write, pointer at start.

w+ : read/write, overwrite or create.

a+ : read/write, pointer at end, create if not exist.

rb+ : binary read/write, pointer at start.

wb+ : binary read/write, overwrite or create.

ab+ : binary append/read/write, pointer at end, create if not exist.

To read a non‑UTF‑8 file, pass the encoding argument, e.g., open('gbk.txt', 'r', encoding='gbk'). If decoding fails, you can use the errors='ignore' parameter.

f = open('gbk.txt', 'r', encoding='gbk', errors='ignore')

4. File object operations

Common methods:

1. f.read(size)

Read up to size bytes; if omitted or negative, reads the whole file.

f = open("1.txt", "r")
content = f.read()
print(content)
f.close()

2. f.readline()

Read a single line, including the newline character.

f = open("1.txt", "r")
line = f.readline()
print(line)
f.close()

3. f.readlines()

Read all lines into a list.

f = open("1.txt", "r")
lines = f.readlines()
print(lines)
f.close()

4. Iterate over a file

# Open a file
f = open("1.txt", "r")
for line in f:
    print(line, end='')
# Close the file
f.close()

5. f.write()

Write a string to the file.

f = open("/tmp/foo.txt", "w")
f.write("Python is a great language.
I love Python!!
")
f.close()

6. f.tell()

Return the current byte offset of the file pointer.

7. f.seek(offset, from_what)

Move the file pointer. from_what can be 0 (start), 1 (current), or 2 (end).

f = open("1.txt", "rb+")
f.write(b"1232312adsfalafds")
print(f.tell())
print(f.seek(5, 0))
print(f.read(1))
print(f.seek(-3, 2))
print(f.read(1))

Result:

8. f.close()

Close the file and release system resources.

5. The with statement

The with statement provides a context manager that automatically closes the file, even if an exception occurs.

with open('test.txt', 'w') as f:
    f.write('Hello, world!')

You can open multiple files in a single with block:

with open('1') as obj1, open('2', 'w') as obj2:
    data = obj1.read()
    obj2.write(data)

6. Summary

This article introduces Python file handling fundamentals, demonstrating how to open files, use various access modes, perform common file object operations, and safely manage resources with the with statement.