Python strings are immutable because once a string is created, its contents cannot be changed. 2 Any operation that appears to modify a string actually creates a new string object in memory. 1

Immutability of strings in Python affects programming in several ways:

• Memory efficiency. 2 Since strings cannot be modified, Python optimizes memory allocation for immutable objects. 2 When a new string object is created, Python can safely allocate memory without worrying about the original object changing. 2
• Security and data integrity. 2 Since strings cannot be modified once created, they are safe from accidental or unauthorized modifications. 2 This is particularly valuable when dealing with sensitive data or when implementing algorithms where the integrity of the data is crucial. 2
• Thread safety. 1 Immutability ensures that string objects are thread-safe and can be safely shared across multiple threads. 1

However, modifying large strings can be memory-intensive and slow, since a new string object must be created every time. 1 In some cases, this can lead to performance issues in a Python program. 1