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diff --git a/Doc/library/parser.rst b/Doc/library/parser.rst index b0e509a..5df8feb 100644 --- a/Doc/library/parser.rst +++ b/Doc/library/parser.rst @@ -24,6 +24,17 @@ from this. This is better than trying to parse and modify an arbitrary Python code fragment as a string because parsing is performed in a manner identical to the code forming the application. It is also faster. +.. note:: + + From Python 2.5 onward, it's much more convenient to cut in at the Abstract + Syntax Tree (AST) generation and compilation stage, using the :mod:`ast` + module. + + The :mod:`parser` module exports the names documented here also with "st" + replaced by "ast"; this is a legacy from the time when there was no other + AST and has nothing to do with the AST found in Python 2.5. This is also the + reason for the functions' keyword arguments being called *ast*, not *st*. + There are a few things to note about this module which are important to making use of the data structures created. This is not a tutorial on editing the parse trees for Python code, but some examples of using the :mod:`parser` module are @@ -34,9 +45,9 @@ internal parser is required. For full information on the language syntax, refer to :ref:`reference-index`. The parser itself is created from a grammar specification defined in the file :file:`Grammar/Grammar` in the standard Python distribution. The parse trees -stored in the AST objects created by this module are the actual output from the +stored in the ST objects created by this module are the actual output from the internal parser when created by the :func:`expr` or :func:`suite` functions, -described below. The AST objects created by :func:`sequence2ast` faithfully +described below. The ST objects created by :func:`sequence2st` faithfully simulate those structures. Be aware that the values of the sequences which are considered "correct" will vary from one version of Python to another as the formal grammar for the language is revised. However, transporting code from one @@ -46,7 +57,7 @@ migrating to an older version of the interpreter will not support more recent language constructs. The parse trees are not typically compatible from one version to another, whereas source code has always been forward-compatible. -Each element of the sequences returned by :func:`ast2list` or :func:`ast2tuple` +Each element of the sequences returned by :func:`st2list` or :func:`st2tuple` has a simple form. Sequences representing non-terminal elements in the grammar always have a length greater than one. The first element is an integer which identifies a production in the grammar. These integers are given symbolic names @@ -69,19 +80,19 @@ of the :keyword:`if` keyword above is representative. The various types of terminal symbols are defined in the C header file :file:`Include/token.h` and the Python module :mod:`token`. -The AST objects are not required to support the functionality of this module, +The ST objects are not required to support the functionality of this module, but are provided for three purposes: to allow an application to amortize the cost of processing complex parse trees, to provide a parse tree representation which conserves memory space when compared to the Python list or tuple representation, and to ease the creation of additional modules in C which manipulate parse trees. A simple "wrapper" class may be created in Python to -hide the use of AST objects. +hide the use of ST objects. The :mod:`parser` module defines functions for a few distinct purposes. The -most important purposes are to create AST objects and to convert AST objects to +most important purposes are to create ST objects and to convert ST objects to other representations such as parse trees and compiled code objects, but there are also functions which serve to query the type of parse tree represented by an -AST object. +ST object. .. seealso:: @@ -94,20 +105,20 @@ AST object. testing node values. -.. _creating-asts: +.. _creating-sts: -Creating AST Objects --------------------- +Creating ST Objects +------------------- -AST objects may be created from source code or from a parse tree. When creating -an AST object from source, different functions are used to create the ``'eval'`` +ST objects may be created from source code or from a parse tree. When creating +an ST object from source, different functions are used to create the ``'eval'`` and ``'exec'`` forms. .. function:: expr(source) The :func:`expr` function parses the parameter *source* as if it were an input - to ``compile(source, 'file.py', 'eval')``. If the parse succeeds, an AST object + to ``compile(source, 'file.py', 'eval')``. If the parse succeeds, an ST object is created to hold the internal parse tree representation, otherwise an appropriate exception is thrown. @@ -115,22 +126,22 @@ and ``'exec'`` forms. .. function:: suite(source) The :func:`suite` function parses the parameter *source* as if it were an input - to ``compile(source, 'file.py', 'exec')``. If the parse succeeds, an AST object + to ``compile(source, 'file.py', 'exec')``. If the parse succeeds, an ST object is created to hold the internal parse tree representation, otherwise an appropriate exception is thrown. -.. function:: sequence2ast(sequence) +.. function:: sequence2st(sequence) This function accepts a parse tree represented as a sequence and builds an internal representation if possible. If it can validate that the tree conforms to the Python grammar and all nodes are valid node types in the host version of - Python, an AST object is created from the internal representation and returned + Python, an ST object is created from the internal representation and returned to the called. If there is a problem creating the internal representation, or if the tree cannot be validated, a :exc:`ParserError` exception is thrown. An - AST object created this way should not be assumed to compile correctly; normal - exceptions thrown by compilation may still be initiated when the AST object is - passed to :func:`compileast`. This may indicate problems not related to syntax + ST object created this way should not be assumed to compile correctly; normal + exceptions thrown by compilation may still be initiated when the ST object is + passed to :func:`compilest`. This may indicate problems not related to syntax (such as a :exc:`MemoryError` exception), but may also be due to constructs such as the result of parsing ``del f(0)``, which escapes the Python parser but is checked by the bytecode compiler. @@ -142,31 +153,31 @@ and ``'exec'`` forms. symbols in the input tree. -.. function:: tuple2ast(sequence) +.. function:: tuple2st(sequence) - This is the same function as :func:`sequence2ast`. This entry point is + This is the same function as :func:`sequence2st`. This entry point is maintained for backward compatibility. -.. _converting-asts: +.. _converting-sts: -Converting AST Objects ----------------------- +Converting ST Objects +--------------------- -AST objects, regardless of the input used to create them, may be converted to +ST objects, regardless of the input used to create them, may be converted to parse trees represented as list- or tuple- trees, or may be compiled into executable code objects. Parse trees may be extracted with or without line numbering information. -.. function:: ast2list(ast[, line_info]) +.. function:: st2list(ast[, line_info]) - This function accepts an AST object from the caller in *ast* and returns a + This function accepts an ST object from the caller in *ast* and returns a Python list representing the equivalent parse tree. The resulting list representation can be used for inspection or the creation of a new parse tree in list form. This function does not fail so long as memory is available to build the list representation. If the parse tree will only be used for inspection, - :func:`ast2tuple` should be used instead to reduce memory consumption and + :func:`st2tuple` should be used instead to reduce memory consumption and fragmentation. When the list representation is required, this function is significantly faster than retrieving a tuple representation and converting that to nested lists. @@ -177,31 +188,31 @@ numbering information. This information is omitted if the flag is false or omitted. -.. function:: ast2tuple(ast[, line_info]) +.. function:: st2tuple(ast[, line_info]) - This function accepts an AST object from the caller in *ast* and returns a + This function accepts an ST object from the caller in *ast* and returns a Python tuple representing the equivalent parse tree. Other than returning a - tuple instead of a list, this function is identical to :func:`ast2list`. + tuple instead of a list, this function is identical to :func:`st2list`. If *line_info* is true, line number information will be included for all terminal tokens as a third element of the list representing the token. This information is omitted if the flag is false or omitted. -.. function:: compileast(ast[, filename='<ast>']) +.. function:: compilest(ast[, filename='<syntax-tree>']) .. index:: builtin: exec builtin: eval - The Python byte compiler can be invoked on an AST object to produce code objects + The Python byte compiler can be invoked on an ST object to produce code objects which can be used as part of a call to the built-in :func:`exec` or :func:`eval` functions. This function provides the interface to the compiler, passing the internal parse tree from *ast* to the parser, using the source file name specified by the *filename* parameter. The default value supplied for *filename* - indicates that the source was an AST object. + indicates that the source was an ST object. - Compiling an AST object may result in exceptions related to compilation; an + Compiling an ST object may result in exceptions related to compilation; an example would be a :exc:`SyntaxError` caused by the parse tree for ``del f(0)``: this statement is considered legal within the formal grammar for Python but is not a legal language construct. The :exc:`SyntaxError` raised for this @@ -211,15 +222,15 @@ numbering information. tree. -.. _querying-asts: +.. _querying-sts: -Queries on AST Objects ----------------------- +Queries on ST Objects +--------------------- -Two functions are provided which allow an application to determine if an AST was +Two functions are provided which allow an application to determine if an ST was created as an expression or a suite. Neither of these functions can be used to -determine if an AST was created from source code via :func:`expr` or -:func:`suite` or from a parse tree via :func:`sequence2ast`. +determine if an ST was created from source code via :func:`expr` or +:func:`suite` or from a parse tree via :func:`sequence2st`. .. function:: isexpr(ast) @@ -229,19 +240,19 @@ determine if an AST was created from source code via :func:`expr` or When *ast* represents an ``'eval'`` form, this function returns true, otherwise it returns false. This is useful, since code objects normally cannot be queried for this information using existing built-in functions. Note that the code - objects created by :func:`compileast` cannot be queried like this either, and + objects created by :func:`compilest` cannot be queried like this either, and are identical to those created by the built-in :func:`compile` function. .. function:: issuite(ast) - This function mirrors :func:`isexpr` in that it reports whether an AST object + This function mirrors :func:`isexpr` in that it reports whether an ST object represents an ``'exec'`` form, commonly known as a "suite." It is not safe to assume that this function is equivalent to ``not isexpr(ast)``, as additional syntactic fragments may be supported in the future. -.. _ast-errors: +.. _st-errors: Exceptions and Error Handling ----------------------------- @@ -257,12 +268,12 @@ function for information about the exceptions it can raise. generally produced for validation failures rather than the built in :exc:`SyntaxError` thrown during normal parsing. The exception argument is either a string describing the reason of the failure or a tuple containing a - sequence causing the failure from a parse tree passed to :func:`sequence2ast` - and an explanatory string. Calls to :func:`sequence2ast` need to be able to + sequence causing the failure from a parse tree passed to :func:`sequence2st` + and an explanatory string. Calls to :func:`sequence2st` need to be able to handle either type of exception, while calls to other functions in the module will only need to be aware of the simple string values. -Note that the functions :func:`compileast`, :func:`expr`, and :func:`suite` may +Note that the functions :func:`compilest`, :func:`expr`, and :func:`suite` may throw exceptions which are normally thrown by the parsing and compilation process. These include the built in exceptions :exc:`MemoryError`, :exc:`OverflowError`, :exc:`SyntaxError`, and :exc:`SystemError`. In these @@ -270,49 +281,49 @@ cases, these exceptions carry all the meaning normally associated with them. Refer to the descriptions of each function for detailed information. -.. _ast-objects: +.. _st-objects: -AST Objects ------------ +ST Objects +---------- -Ordered and equality comparisons are supported between AST objects. Pickling of -AST objects (using the :mod:`pickle` module) is also supported. +Ordered and equality comparisons are supported between ST objects. Pickling of +ST objects (using the :mod:`pickle` module) is also supported. -.. data:: ASTType +.. data:: STType The type of the objects returned by :func:`expr`, :func:`suite` and - :func:`sequence2ast`. + :func:`sequence2st`. -AST objects have the following methods: +ST objects have the following methods: -.. method:: AST.compile([filename]) +.. method:: ST.compile([filename]) - Same as ``compileast(ast, filename)``. + Same as ``compilest(st, filename)``. -.. method:: AST.isexpr() +.. method:: ST.isexpr() - Same as ``isexpr(ast)``. + Same as ``isexpr(st)``. -.. method:: AST.issuite() +.. method:: ST.issuite() - Same as ``issuite(ast)``. + Same as ``issuite(st)``. -.. method:: AST.tolist([line_info]) +.. method:: ST.tolist([line_info]) - Same as ``ast2list(ast, line_info)``. + Same as ``st2list(st, line_info)``. -.. method:: AST.totuple([line_info]) +.. method:: ST.totuple([line_info]) - Same as ``ast2tuple(ast, line_info)``. + Same as ``st2tuple(st, line_info)``. -.. _ast-examples: +.. _st-examples: Examples -------- @@ -340,27 +351,27 @@ to the code :: 10 The equivalent operation using the :mod:`parser` module is somewhat longer, and -allows the intermediate internal parse tree to be retained as an AST object:: +allows the intermediate internal parse tree to be retained as an ST object:: >>> import parser - >>> ast = parser.expr('a + 5') - >>> code = ast.compile('file.py') + >>> st = parser.expr('a + 5') + >>> code = st.compile('file.py') >>> a = 5 >>> eval(code) 10 -An application which needs both AST and code objects can package this code into +An application which needs both ST and code objects can package this code into readily available functions:: import parser def load_suite(source_string): - ast = parser.suite(source_string) - return ast, ast.compile() + st = parser.suite(source_string) + return st, st.compile() def load_expression(source_string): - ast = parser.expr(source_string) - return ast, ast.compile() + st = parser.expr(source_string) + return st, st.compile() Information Discovery @@ -414,8 +425,8 @@ tuples. :: >>> import parser >>> import pprint - >>> ast = parser.suite(open('docstring.py').read()) - >>> tup = ast.totuple() + >>> st = parser.suite(open('docstring.py').read()) + >>> tup = st.totuple() >>> pprint.pprint(tup) (257, (264, @@ -670,8 +681,8 @@ file :file:`example.py`.) :: source = open(fileName).read() basename = os.path.basename(os.path.splitext(fileName)[0]) - ast = parser.suite(source) - return ModuleInfo(ast.totuple(), basename) + st = parser.suite(source) + return ModuleInfo(st.totuple(), basename) This provides an easy-to-use interface to the documentation of a module. If information is required which is not extracted by the code of this example, the |