How Can We Efficiently Count Overlapping Substring Occurrences in Python?

Counting Overlapping String Occurrences Effectively

Identifying the number of occurrences of a substring within a string can be tricky, especially when overlaps are allowed. Libraries like Python's string provide built-in methods like 'count' for this purpose, but they do not consider overlapping instances.

Overlapping Character Counting

Consider the following approach:

def overlapping_count(string, substring):
    count = 0
    for i in range(len(string) - len(substring) + 1):
        if string[i:i+len(substring)] == substring:
            count += 1
    return count

Here, the function iterates through the string, examining substrings of the specified length and incrementing the count when a match is found. This method is straightforward but can be relatively slow for large strings.

A Potential Optimization

For performance reasons, it's worth exploring a different approach that involves utilizing Cython's capabilities:

import cython

@cython.boundscheck(False)
def faster_occurrences(string, substring):
    cdef int count = 0
    cdef int start = 0
    while True:
        start = string.find(substring, start) + 1
        if start > 0:
            count += 1
        else:
            return count

With Cython, we can take advantage of static type declarations and Just-In-Time (JIT) compilation to improve performance by skipping unnecessary type checks and optimizations for Python code. This optimized function should be significantly faster for larger data sets.

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