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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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