pylcs - Longest Common Subsequence

0.1.1 · maintenance · verified Fri Apr 17

pylcs is a Python library that provides a highly optimized C++ implementation of the Longest Common Subsequence (LCS) algorithm. It is currently at version 0.1.1 and offers a fast way to compute the length of the LCS between two strings. The project appears to have an infrequent release cadence, with the last update in late 2022.

Common errors

```
ModuleNotFoundError: No module named 'pylcs'
```
cause The 'pylcs' package is not installed in your current Python environment, or the installation failed.

fix Run `pip install pylcs` to install the package. If it still fails, check for C++ compiler requirements.
```
TypeError: lcs() takes exactly 2 arguments (1 given)
```
cause The `lcs` function was called with an incorrect number of arguments. It requires exactly two string arguments.

fix Ensure you pass two string arguments to `lcs`, e.g., `lcs(string_a, string_b)`.
```
TypeError: argument 1 must be str, not list
```
cause You attempted to pass a non-string type (e.g., a list, int, or dict) to the `lcs` function, which strictly expects string inputs.

fix Convert all inputs to strings before calling `lcs`. For example, `lcs(str(my_list_item), str(my_other_item))`.

Warnings

gotcha pylcs only returns the length of the LCS, not the actual subsequence itself. If you need the subsequence string, you'll need to implement or use another library's function for reconstruction.
Fix: For the actual LCS string, consider using `difflib.SequenceMatcher` from the standard library or a custom implementation if performance is critical.
gotcha The library primarily accepts string inputs. Passing non-string types (e.g., lists, numbers) will result in a TypeError. Ensure both arguments passed to `lcs` are strings.
Fix: Always cast inputs to strings before passing them to `pylcs.lcs`, e.g., `lcs(str(item1), str(item2))`.
gotcha As a C++ extension, installation of `pylcs` requires a C++ compiler (like GCC on Linux/macOS or MSVC on Windows) to be present and configured on your system. Installation might fail without it.
Fix: Ensure you have a C++ compiler installed. On Windows, install 'Build Tools for Visual Studio'. On Linux/macOS, install `build-essential` or Xcode command line tools respectively.

Install

pip install pylcs Install pylcs

Imports

lcs
```
from pylcs import lcs
```

Quickstart

This example demonstrates how to import the `lcs` function and use it to calculate the length of the longest common subsequence between two strings. The function expects two string arguments.

from pylcs import lcs

str1 = "ABCBDAB"
str2 = "BDCABA"

# Get the length of the longest common subsequence
lcs_length = lcs(str1, str2)

print(f"Strings: '{str1}', '{str2}'")
print(f"Length of LCS: {lcs_length}")

# Example with different strings
str3 = "AGGTAB"
str4 = "GXTXAYB"
print(f"\nStrings: '{str3}', '{str4}'")
print(f"Length of LCS: {lcs(str3, str4)}")

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