How to Convert CamelCase to snake_case in Python Elegantly?

Elegant Python function to convert CamelCase to snake_case?

Converting from CamelCase to snake_case in Python requires a simple yet elegant approach. This article explores several effective methods to achieve this transformation, addressing variations in naming conventions and providing clear examples.

Using Regular Expressions with Lookahead/Lookbehind

The most versatile method utilizes regular expressions with lookahead and lookbehind assertions:

<code class="python">import re

def camel_to_snake(name):
    name = re.sub(r'(?<!^)(?=[A-Z])', '_', name).lower()
    return name</code>

This pattern matches boundaries between uppercase and lowercase characters, inserting underscores while simultaneously converting to lowercase.

Alternative Regex Patterns

For more complex cases, here's an alternative regex with alternation:

<code class="python">pattern = re.compile(r"(\w+)([A-Z]\w+)")
name = "_".join(pattern.findall(name))</code>

This pattern handles cases where multiple uppercase letters appear consecutively.

To avoid converting "HTTPHeader" to "h_t_t_p_header," use the following pattern:

<code class="python">pattern = re.compile(r"([a-z])([A-Z])")
name = "_".join(pattern.findall(name))</code>

Multi-Pass Substitutions

An alternative approach avoids using lookahead/lookbehind:

<code class="python">def camel_to_snake(name):
    name = re.sub('(.)([A-Z][a-z]+)', r'_', name)
    return re.sub('([a-z0-9])([A-Z])', r'_', name).lower()</code>

This approach combines two substitution passes to handle various naming conventions.

Snake Case to Pascal Case

For completeness, here's a function to convert snake_case to PascalCase:

<code class="python">def snake_to_pascal(name):
    name = ''.join(word.title() for word in name.split('_'))
    return name</code>

These functions provide a comprehensive solution to CamelCase and snake_case transformations in Python, catering to various naming conventions.

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