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Python re purge() method

The Python re.purge() method is used to clear the regular expression cache. Python's re module maintains a cache of compiled regular expressions to improve performance but this cache can grow if many different patterns are compiled. Using the re.purge() method we can clear this cache by freeing up memory and ensuring that old or unused patterns do not remain in memory.

This method is particularly useful in long-running programs or environments where memory usage is a concern such as web servers or applications that compile many unique regular expressions over time.

Following is the syntax and parameters of Python re.purge() method.

re.purge()

This method does not take any parameters.

This method does not return any values.

Following is the example of re.purge() method which clears the cache after compiling and using some regular expressions −

import re

# Compile some regular expressions
pattern1 = re.compile(r'\d+')
pattern2 = re.compile(r'\w+')

# Use the patterns
pattern1.search('123')
pattern2.search('abc')

# Clear the cache
re.purge()

# After purge, the cache is empty
# Compile the same patterns again
pattern1 = re.compile(r'\d+')
pattern2 = re.compile(r'\w+')

print("Cache cleared and patterns recompiled.") 

Cache cleared and patterns recompiled.

This example shows how to measure the memory usage of the regular expression cache before and after using the method re.purge(). This can show the impact of clearing the cache on memory usage −

import re
import sys

# Compile many regular expressions to fill the cache
patterns = [re.compile(rf'\d+_{i}') for i in range(1000)]

# Measure memory usage of the cache
before_purge = sys.getsizeof(re._cache)

# Clear the cache
re.purge()

# Measure memory usage of the cache after purge
after_purge = sys.getsizeof(re._cache)

print(f"Memory usage before purge: {before_purge} bytes")
print(f"Memory usage after purge: {after_purge} bytes")

Memory usage before purge: 36952 bytes
Memory usage after purge: 64 bytes

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