PYTHON PROGRAM • EXCEPTIONS & FILES
Count Lines in a File in Python
Learn count lines in a file in python with a short, executable Python example.
PROBLEM UNDERSTANDING
Input and expected output
No input required
3
COMPLETE PYTHON PROGRAM
Complete Python implementation
from pathlib import Path
path = Path('topics.txt')
path.write_text('Basics\nLoops\nFunctions\n', encoding='utf-8')
with path.open(encoding='utf-8') as file:
print(sum(1 for _ in file))CURRENT STEP
Select Start to walk through the important lines.
SELECTED LINE
No line selected
EXPECTED OUTPUT FOR THE SAMPLE
3
PROGRAM EXPLANATION
Algorithm and explanation
- Import the required standard-library tools and prepare the sample data for count lines in a file.
- Process the data step by step using File iteration and Generator.
- Display the result for count lines in a file and compare it with the documented sample output.
This example of count lines in a file processes the sample values in a controlled iteration. It demonstrates File iteration and Generator and prints a deterministic result that can be checked against the sample output.
EFFICIENCY
Time and space complexity
O(n)
O(n)
DEBUGGING CHECKLIST
Common mistakes
For count lines in a file, keep the data shape and value types consistent with File iteration.
Keep every dependent statement inside the correct indented Python block.
Use the intended file mode and encoding, and let the context manager close the resource.