Reference library

Comprehensions & generators

List/dict/set comprehensions, generator expressions, and lazy iteration.

4 matches

Build a lazy generator to read file lines in Python

Create a generator function that yields file lines one at a time, avoiding loading the entire file into memory, and demonstrate its lazy processing.

generator file-io lazy

Python

def lazy_lines(filepath):
    """Yield lines from a file one at a time without loading the whole file into memory."""
    with open(filepath, 'r', encoding='utf-8') as file:
        for line in file:
            yield line.rstrip('\n')


if __name__ == "__main__":
    # Create a sample file to demonstrate
    sample_c…

14 0 Open

Comprehensions & generators easy

How to Lazily Transform Items in Python with a Generator

Map a transform function over an iterable lazily with a generator so items are processed on demand, not up front.

generators lazy evaluation mapping

Python

def lazy_map(items, transform):
    for item in items:
        yield transform(item)

def double(x):
    return x * 2

def upper(s):
    return s.upper()

if __name__ == "__main__":
    numbers = [1, 2, 3, 4, 5]
    doubled = lazy_map(numbers, double)
    print("Doubled numbers:", end=" ")
    for value in doubled:
  …

14 0 Open

Comprehensions & generators easy

How to Parse CSV Rows as Generator Dicts in Python

Reads a CSV file and yields each row as a dictionary one at a time using a generator, so the file is processed lazily.

csv generator parsing

Python

import csv
from pathlib import Path

def csv_to_dicts(filepath):
    with open(filepath, mode="r", newline="", encoding="utf-8") as file:
        reader = csv.DictReader(file)
        for row in reader:
            yield row

if __name__ == "__main__":
    sample_csv = Path("sample_data.csv")
    sample_csv.write_text…

13 0 Open

Comprehensions & generators easy

Memory efficient map over large file in Python

A generator-based streaming map that processes a large file line by line without loading the whole file into memory.

generator file-io streaming

Python

import sys

def process_lines(file_path):
    """Memory-efficient map over a large file: yields processed lines."""
    with open(file_path, 'r') as f:
        for line in f:
            # Example mapping: strip whitespace and uppercase
            yield line.strip().upper()

if __name__ == "__main__":
    # Use a sma…

12 0 Open

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