What is the naming convention in Python for variable and function names?

See Python PEP 8: Function and Variable Names:

Function names should be lowercase, with words separated by underscores as necessary to improve readability.

Variable names follow the same convention as function names.

mixedCase is allowed only in contexts where that's already the prevailing style (e.g. threading.py), to retain backwards compatibility.

The Google Python Style Guide has the following convention:

module_name, package_name, ClassName, method_name, ExceptionName, function_name, GLOBAL_CONSTANT_NAME, global_var_name, instance_var_name, function_parameter_name, local_var_name.

A similar naming scheme should be applied to a CLASS_CONSTANT_NAME

David Goodger (in "Code Like a Pythonista" here) describes the PEP 8 recommendations as follows:

• joined_lower for functions, methods, attributes, variables

• joined_lower or ALL_CAPS for constants

• StudlyCaps for classes

• camelCase only to conform to pre-existing conventions