File Methods (read, readline, write)0%
File Methods (read, readline, write)
Beginner9 min read•Updated: 2026-09-03
File Methods (read, readline, write)
Understand position pointers and reading granularity with file methods.
Key Concepts & Detailed Explanation
File navigation methods:
- .read(size): Reads entire file (or up to 'size' bytes).
- .readline(): Reads a single line ending in \n.
- .readlines(): Reads all lines and returns them as a list of strings.
- .tell(): Returns current byte position of the file pointer.
- .seek(offset, whence): Moves file pointer to specified byte offset.
Code Examples & Output
Python
# Demonstrate seek and tell
with open("cursor_demo.txt", "w+") as f:
f.write("0123456789ABCDEF")
print("Pointer at end:", f.tell()) # 16
f.seek(0) # Reset to beginning
print("Read first 5 chars:", f.read(5)) # "01234"
print("Pointer now:", f.tell()) # 5
f.seek(10)
print("Read from position 10:", f.read()) # "ABCDEF"
Expected Output:
Output
Pointer at end: 16
Read first 5 chars: 01234
Pointer now: 5
Read from position 10: ABCDEF
Best Practices & Common Pitfalls
Use 'f.seek(0)' to rewind a file back to the beginning after reading it once.
Practice Quiz
1. What method rewinds the file read pointer back to the start of the file?
- A) f.rewind()
- B) f.seek(0)
- C) f.reset()
- D) f.start()
Answer: B
Explanation: f.seek(0) resets the file pointer to byte 0.
2. What does f.tell() return?
- A) Line number
- B) Current byte offset position in the file
- C) File size
- D) Character count
Answer: B
Explanation: f.tell() returns the current integer position in bytes.
Practice Challenge
Write a program that writes 5 lines of text to a file, rewinds with seek(0), and prints only the 3rd line using readline().
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|---|---|
| Working with open() | Contact Book |
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