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3. Python Runtime Services

The modules described in this chapter provide a wide range of services related to the Python interpreter and its interaction with its environment. Here's an overview:

`sys` | Access system-specific parameters and functions.
`gc` | Interface to the cycle-detecting garbage collector.
`atexit` | Register and execute cleanup functions.
`types` | Names for all built-in types.
`UserDict` | Class wrapper for dictionary objects.
`UserList` | Class wrapper for list objects.
`UserString` | Class wrapper for string objects.
`operator` | All Python's standard operators as built-in functions.
`traceback` | Print or retrieve a stack traceback.
`linecache` | This module provides random access to individual lines from text files.
`pickle` | Convert Python objects to streams of bytes and back.
`cPickle` | Faster version of `pickle`, but not subclassable.
`copy_reg` | Register `pickle` support functions.
`shelve` | Python object persistence.
`copy` | Shallow and deep copy operations.
`marshal` | Convert Python objects to streams of bytes and back (with different constraints).
`imp` | Access the implementation of the `import` statement.
`code` | Base classes for interactive Python interpreters.
`codeop` | Compile (possibly incomplete) Python code.
`pprint` | Data pretty printer.
`repr` | Alternate `repr()` implementation with size limits.
`new` | Interface to the creation of runtime implementation objects.
`site` | A standard way to reference site-specific modules.
`user` | A standard way to reference user-specific modules.
`__builtin__` | The set of built-in functions.
`__main__` | The environment where the top-level script is run.