32.3. symtable — Access to the compiler’s symbol tables — Python 2.7.18 documentation

This document is for an old version of Python that is no longer supported. You should upgrade and read the Python documentation for the current stable release.

# 32.3. `symtable` — Access to the compiler’s symbol tables

Source code: Lib/symtable.py

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. `symtable` provides an interface to examine these tables.

## 32.3.1. Generating Symbol Tables

`symtable.` `symtable`(code, filename, compile_type)

  Return the toplevel `SymbolTable` for the Python source code. filename is the name of the file containing the code. compile_type is like the mode argument to `compile()`.

## 32.3.2. Examining Symbol Tables

class `symtable.` `SymbolTable`

  A namespace table for a block. The constructor is not public.

  `get_type`()

    Return the type of the symbol table. Possible values are `'class'`, `'module'`, and `'function'`.

  `get_id`()

    Return the table’s identifier.

  `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 (`get_type()` returns `'module'`).

  `get_lineno`()

    Return the number of the first line in the block this table represents.

  `is_optimized`()

    Return `True` if the locals in this table can be optimized.

  `is_nested`()

    Return `True` if the block is a nested class or function.

  `has_children`()

    Return `True` if the block has nested namespaces within it. These can be obtained with `get_children()`.

  `has_exec`()

    Return `True` if the block uses `exec`.

  `has_import_star`()

    Return `True` if the block uses a starred from-import.

  `get_identifiers`()

    Return a list of names of symbols in this table.

  `lookup`(name)

    Lookup name in the table and return a `Symbol` instance.

  `get_symbols`()

    Return a list of `Symbol` instances for names in the table.

  `get_children`()

    Return a list of the nested symbol tables.

class `symtable.` `Function`

  A namespace for a function or method. This class inherits `SymbolTable`.

  `get_parameters`()

    Return a tuple containing names of parameters to this function.

  `get_locals`()

    Return a tuple containing names of locals in this function.

  `get_globals`()

    Return a tuple containing names of globals in this function.

  `get_frees`()

    Return a tuple containing names of free variables in this function.

class `symtable.` `Class`

  A namespace of a class. This class inherits `SymbolTable`.

  `get_methods`()

    Return a tuple containing the names of methods declared in the class.

class `symtable.` `Symbol`

  An entry in a `SymbolTable` corresponding to an identifier in the source. The constructor is not public.

  `get_name`()

    Return the symbol’s name.

  `is_referenced`()

    Return `True` if the symbol is used in its block.

  `is_imported`()

    Return `True` if the symbol is created from an import statement.

  `is_parameter`()

    Return `True` if the symbol is a parameter.

  `is_global`()

    Return `True` if the symbol is global.

  `is_declared_global`()

    Return `True` if the symbol is declared global with a global statement.

  `is_local`()

    Return `True` if the symbol is local to its block.

  `is_free`()

    Return `True` if the symbol is referenced in its block, but not assigned to.

  `is_assigned`()

    Return `True` if the symbol is assigned to in its block.

  `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.

  `get_namespaces`()

    Return a list of namespaces bound to this name.

  `get_namespace`()

    Return the namespace bound to this name. If more than one namespace is bound, a `ValueError` is raised.