File Read Backwards

3.2.0 · active · verified Thu Apr 16

file-read-backwards is a Python library (current version 3.2.0) providing a memory-efficient way to read text files line-by-line starting from the end of the file. It supports ASCII, Latin-1, and UTF-8 encodings, and handles various newline characters (\r, \r\n, \n). The library is actively maintained with a stable release cadence.

Common errors

```
ImportError: cannot import name 'FileReadBackwardsIterator'
```
cause This error occurs when attempting to import an internal, non-public class named `FileReadBackwardsIterator` directly. This class is not intended for public use and may have been refactored or not exposed at the top level of the package.

fix The main class for backward file reading is `FileReadBackwards`. Use `from file_read_backwards import FileReadBackwards` instead.
```
MemoryError / Application hangs when trying to read large files in reverse.
```
cause Attempting to read large files into memory entirely (e.g., using `file.readlines()` and then reversing the list) consumes excessive RAM, leading to `MemoryError` or very slow processing, especially on systems with limited memory.

fix Utilize `file-read-backwards` as intended for memory-efficient processing. It reads files in chunks from the end, avoiding loading the entire file into memory. Example: `with FileReadBackwards('large_file.txt') as frb: for line in frb: ...`

Warnings

breaking In version 2.0.0, the internal behavior of `FileReadBackwards` changed; it no longer creates multiple iterators. Additionally, the `readline()` method was introduced, which returns one line at a time with `os.linesep` as the trailing newline, potentially altering behavior for users migrating from 1.x versions.
Fix: Review code that implicitly relied on old iterator behavior or the exact newline characters returned by `readline()` in 1.x. Explicitly strip newlines if strict control is needed (`line.strip()`).
gotcha While the library supports `ascii`, `latin-1`, and `utf-8` encodings, incorrect specification of the `encoding` parameter or attempting to read files with inconsistent or unsupported encodings can lead to `UnicodeDecodeError` or unexpected output.
Fix: Always specify the correct encoding for your file if it's known. If uncertain, `utf-8` is a common default, but verify file content for other encodings, especially `latin-1` or `cp1252` for legacy files.

Install

pip install file-read-backwards Install stable release

Imports

FileReadBackwards

from file_read_backwards import FileReadBackwards

Quickstart

Demonstrates reading a file line by line from the end using the context manager and iterating over the lines.

import os
from file_read_backwards import FileReadBackwards

# Create a dummy file for demonstration
file_path = "example_log.txt"
with open(file_path, "w", encoding="utf-8") as f:
    f.write("Line 1\n")
    f.write("Line 2\n")
    f.write("Line 3\n")
    f.write("Line 4\n")

print(f"Reading '{file_path}' backwards:")
with FileReadBackwards(file_path, encoding="utf-8") as frb:
    for line in frb:
        print(line.strip())

# Clean up the dummy file
os.remove(file_path)

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