:mod:`symtable` --- Access to the compiler's symbol tables
==========================================================
.. module:: symtable
:synopsis: Interface to the compiler's internal symbol tables.
**Source code:** :source:`Lib/symtable.py`
--------------
.. moduleauthor:: Jeremy Hylton <jeremy@alum.mit.edu>
.. sectionauthor:: Benjamin Peterson <benjamin@python.org>
Symbol tables are generated by the compiler from AST just before bytecode is
generated. The symbol table is responsible for calculating the scope of every
identifier in the code. :mod:`symtable` provides an interface to examine these
tables.
Generating Symbol Tables
------------------------
.. function:: symtable(code, filename, compile_type)
Return the toplevel :class:`SymbolTable` for the Python source *code*.
*filename* is the name of the file containing the code. *compile_type* is
like the *mode* argument to :func:`compile`.
Examining Symbol Tables
-----------------------
.. class:: SymbolTable
A namespace table for a block. The constructor is not public.
.. method:: get_type()
Return the type of the symbol table. Possible values are ``'class'``,
``'module'``, and ``'function'``.
.. method:: get_id()
Return the table's identifier.
.. method:: get_name()
Return the table's name. This is the name of the class if the table is
for a class, the name of the function if the table is for a function, or
``'top'`` if the table is global (:meth:`get_type` returns ``'module'``).
.. method:: get_lineno()
Return the number of the first line in the block this table represents.
.. method:: is_optimized()
Return ``True`` if the locals in this table can be optimized.
.. method:: is_nested()
Return ``True`` if the block is a nested class or function.
.. method:: has_children()
Return ``True`` if the block has nested namespaces within it. These can
be obtained with :meth:`get_children`.
.. method:: get_identifiers()
Return a view object containing the names of symbols in the table.
See the :ref:`documentation of view objects <dict-views>`.
.. method:: lookup(name)
Lookup *name* in the table and return a :class:`Symbol` instance.
.. method:: get_symbols()
Return a list of :class:`Symbol` instances for names in the table.
.. method:: get_children()
Return a list of the nested symbol tables.
.. class:: Function
A namespace for a function or method. This class inherits
:class:`SymbolTable`.
.. method:: get_parameters()
Return a tuple containing names of parameters to this function.
.. method:: get_locals()
Return a tuple containing names of locals in this function.
.. method:: get_globals()
Return a tuple containing names of globals in this function.
.. method:: get_nonlocals()
Return a tuple containing names of nonlocals in this function.
.. method:: get_frees()
Return a tuple containing names of free variables in this function.
.. class:: Class
A namespace of a class. This class inherits :class:`SymbolTable`.
.. method:: get_methods()
Return a tuple containing the names of methods declared in the class.
.. class:: Symbol
An entry in a :class:`SymbolTable` corresponding to an identifier in the
source. The constructor is not public.
.. method:: get_name()
Return the symbol's name.
.. method:: is_referenced()
Return ``True`` if the symbol is used in its block.
.. method:: is_imported()
Return ``True`` if the symbol is created from an import statement.
.. method:: is_parameter()
Return ``True`` if the symbol is a parameter.
.. method:: is_global()
Return ``True`` if the symbol is global.
.. method:: is_nonlocal()
Return ``True`` if the symbol is nonlocal.
.. method:: is_declared_global()
Return ``True`` if the symbol is declared global with a global statement.
.. method:: is_local()
Return ``True`` if the symbol is local to its block.
.. method:: is_annotated()
Return ``True`` if the symbol is annotated.
.. versionadded:: 3.6
.. method:: is_free()
Return ``True`` if the symbol is referenced in its block, but not assigned
to.
.. method:: is_assigned()
Return ``True`` if the symbol is assigned to in its block.
.. method:: is_namespace()
Return ``True`` if name binding introduces new namespace.
If the name is used as the target of a function or class statement, this
will be true.
For example::
>>> table = symtable.symtable("def some_func(): pass", "string", "exec")
>>> table.lookup("some_func").is_namespace()
True
Note that a single name can be bound to multiple objects. If the result
is ``True``, the name may also be bound to other objects, like an int or
list, that does not introduce a new namespace.
.. method:: get_namespaces()
Return a list of namespaces bound to this name.
.. method:: get_namespace()
Return the namespace bound to this name. If more than one or no namespace
is bound to this name, a :exc:`ValueError` is raised.
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