Which is Faster: String Concatenation with = or str.join() in Python?

Speed Comparison of Python's String Concatenation vs. str.join

In light of discussions in a previous answer, the speed difference between string concatenation using the = operator and ''.join() has come into question. This article will explore the performance gap between these two approaches.

Method 1: String Concatenation

In the = approach, strings are appended one character at a time. This process involves creating a new string object for each concatenation, leading to significant overhead. Here's a Python code snippet demonstrating the implementation:

<code class="python">def method1():
  out_str = ''
  for num in xrange(loop_count):
    out_str += 'num'
  return out_str</code>

Method 4: str.join()

In contrast, ''.join() works by creating a list of strings first, and then joining them into a single string. This avoids the creation of intermediate string objects:

<code class="python">def method4():
  str_list = []
  for num in xrange(loop_count):
    str_list.append('num')
  return ''.join(str_list)</code>

Comparison Results

Empirical tests have shown that string join is significantly faster than concatenation. The reason lies in the immutability of strings in Python. Each concatenation operation requires the creation of a new string object, resulting in performance degradation.

The following graph illustrates the speed difference between the two methods:

[Image of a graph comparing the performance of method1 and method4]

Conclusion

When dealing with large strings or repeated concatenation operations, ''.join() offers a substantial performance advantage over the = operator. Utilizing ''.join() optimizes string concatenation by minimizing the creation of intermediate string objects and leveraging Python's efficient list handling capabilities.

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