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3. Python 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.
`types` | Names for all built-in types.
`UserDict` | Class wrapper for dictionary objects.
`UserList` | Class wrapper for list objects.
`operator` | All Python's standard operators as built-in functions.
`traceback` | Print or retrieve a stack traceback.
`pickle` | Convert Python objects to streams of bytes and back.
`cPickle` | Faster version of \modulepickle, but not subclassable.
`copy_reg` | Register \modulepickle support functions.
`shelve` | Python object persistency.
`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 \keywordimport statement.
`parser` | Access parse trees for Python source code.
`symbol` | Constants representing internal nodes of the parse tree.
`token` | Constants representing terminal nodes of the parse tree.
`keyword` | Test whether a string is a keyword in Python.
`tokenize` | Lexical scanner for Python source code.
`pyclbr` | Supports information extraction for a Python class browser.
`code` | Code object services.
`pprint` | Data pretty printer.
`repr` | Alternate \functionrepr() implementation with size limits.
`py_compile` | Compile Python source files to byte-code files.
`compileall` | Tools for byte-compiling all Python source files in a directory tree.
`dis` | Disassembler.
`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.